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Ternary Solid Solutions Crystallizing From Ternary Liquids - One Complete Solid Solution System, Two Partial Solid Solution Systems - Crystallization Path - Isothermal and Vertical Sections - V. Solid Solution Systems With Three Phase Equilibria - VI. Solid Solution Systems With Four Phase Equilibria - VII.
Page/Link:Page URL:HTML link:The Free Library. Retrieved Sep 25 2019 fromResearch in phase equilibria and crystallography has been a tradition in the Ceramics Division at National Bureau of Standards/National Institute of Standatrds and Technology (NBS/NIST) since the early thirties. In the early years, effort was concentrated in areas of Portland cement, ceramic glazes and glasses, instrument bearings, and battery materials.
In the past 40 years, a large portion of the work was related to electronic materials, including ferroelectrics, piezoelectrics, ionic conductors, dielectrics, microwave dielectrics, and high-temperature superconductors. As a result of the phase equilibria studies, many new compounds have been discovered. Some of these discoveries have had a significant impact on US industry. Structure determinations of these new phases have often been carried out as a joint effort among NS/NIST colleagues and also with outside collaborators using both single crystal and neutron and x-ray powder diffraction techniques. All phase equilibria diagrams were included in Phase Diag rams for Ceramists. Which are collaborative publications between The American Ceramic Society (ACerS) and NBS/NIST.
All x-ray powder diffraction patterns have been included in the Powder Diffraction File (PDF). This article gives a brief account of the history of the development of the phase equilibria and crystallographic research on ceramic oxides in the Ceramics Division. Represented systems, particularly electronic materials, are highlighted.Key words: ceramic oxides; crystal chemistry; crystallography; electronic materials; historical development; phase equilibria. IntroductionPhase diagrams are critical research tools for many scientific disciplines, including material science, ceramics, geology, physics, metallurgy, chemical engineering, and chemistry.
Phase diagrams can be regarded as 'road maps' for materials processing. These diagrams contain important information for the development of new materials, control of structure and composition of critical phases, and improvement of properties of technologically important materials. Applications of phase diagrams range from the preparation of high quality single crystals, single-phase bulk materials, deliberate precipitation of second phases, to the formation of melts. Studies of phase equilibria and crystallography of materials are strongly correlated. Crystallographic information is critical for furthering the understanding of phase equilibria, crystal chemistry, physical properties of materials, and performing various theoretical calculations.Phase equlibria and crystallographic research at NBS/NIST has been an important program since the 1930s. Development of new technologies based on ceramic oxides continued to require new materials and new equipment. As a result, a large number of new phases in a diverse area of material science have been discovered and characterized at NBS/NIST.
Methods of structural characterization include single crystal x-ray, powder neutron and x-ray methods, and electron diffraction. Since powder x-ray diffraction patterns are critical for phase identification, patterns of the new phases were also prepared and were included in the Powder Diffraction File (PDF (1)). Throughout these years, NBS/NIST has collaborated with various important ceramic industries, and the systems investigated reflected the changing emphasis of material systems, including cement, glasses, battery materials, dielectrics, ferroelectrics, ionic conductors, superconductors, microwave materials, magnetic materials, and materials for optical application s.In the following, highlights of the phase equilibria and crystallographic research of oxide materials in the Ceramics Division will be followed by more detailed discussions pertaining to the dielectric and superconductor systems.2. Historical Development2.1 The Early Years (1930s to mid 1960s)In the twenties, the Clay and Silicate Product Division at NBS (which later became the Ceramics Division) had seven Sections that were all product-oriented.
Examples of these sections were 'Heavy Clay Products', 'White Ware', 'Enamels', and 'Lime and Gypsum'. The functions of these Sections were primarily to develop specifications and to perform testing for government agencies. As an example, bricks were tested for water absorption and for resistance to freezing and thawing as a preliminary to writing specifications. The idea of either 'crystallography' or 'phase equilibria' of materials was hardly considered. Between the 1930s and mid 1960s, H. McMurdie and his colleagues pioneered the studies of the phase relationships and crystallographic aspects of ceramic materials.
A portion of the study was also conducted in collaboration with both internal and external laboratories. 2.1.1 Portland CementOne of the early phase diagram studies was reported in 1936 on the formation of MgO in the compositions of Portland cement (2). Portland cement clinker consists essentially of lime, alumina, silica, ferric oxide, and magnesia. The last two phases may be generally considered as occurring incidentally, as impurities in the basic raw material.
Since MgO could be harmful in cement, it would be important to determine its behavior in the cement to establish the composition ranges within which MgO appears as a primary phase (the first crystalline phase to appear on cooling a composition from the liquid state). This work was completed primarily by quenching and petrographic microscopy. Figure 1 shows the phase diagram of the CaO-MgO-2CaO.SiO.sub.2-5CaO.3Al.sub.2O.sub.3 system. The surface intersecting the sides of the tetrahedron at A-B-C-D-E-F-G indicates the lower level (4% to 5%) of the primary phase field (the locus of all compositions in a phase diagram having a common primary phase) of MgO. MgO has an exc eptionally large primary phase field.The structural characterization of the products of hydration of Portland cement was carried out by petrographic and powder x-ray techniques (3) with the phases synthesized by hydrothermal methods. The main finding was that the group of compounds Ca.sub.3Al.sub.2Si.sub.3O.sub.12 (andradite), Ca.sub.3Fe.sub.2Si.sub.3O.sub.12 (grossularite), Ca.sub.3Al.sub.3H.sub.12O.sub.12 and Ca.sub.3Fe.sub.2H.sub.12O.sub.12 form a complete series of solid solutions, with a garnet structure. The phases with hydrogen were called hydrogarnets.
All these compounds were found to be cubic with space group Ia 3d.2.1.2 Ceramic Glazes and GlassesIn the thirties, information on phases in the PbO-SiO.sub.2 system was needed in connection with the studies of ceramic glazes and glasses. Four phases were found in this system and their x-ray diffraction patterns were determined by Geller et al. (4), and McMurdie and Bunting (5).
These studies used both x-ray diffraction and petrographic microscopy methods. In addition, x-ray patterns of phases of the K.sub.2O-PbO-SiO.sub.2, PbO-SiO.sub.2, and the Na.sub.2-PbO-SiO.sub.2 systems were prepared in cooperation with the Whiteware Section.In the late forties, phase equilibrium information for the system BaO-B.sub.2O.sub.3-SiO.sub.3 and the subsystem BaOB.sub.2O.sub.3 (6) were of importance to the glass industry as a starting point for the investigations of barium crown glasses (see Fig. These glasses are characterized by high refractive index and low dispersion.
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The experiments included quenchings and the use of differential thermal analysis (DTA). Phases were identified by microscopy and x-ray diffraction. X-ray patterns of four phases including the low form of BaB.sub.2O.sub.4 were reported in the BaO-B.sub.2O.sub.3 system. A two-liquid region (liquid immiscibility) was found. In the ternary system BaOB.sub.2O.sub.3-SiO.sub.2 system (7), one ternary phase, Ba.sub.3B.sub.6Si.sub.2O.sub.16, was discovered and a large two-liquid region was also located (Fig. The system BaO-SiO.sub.2 was later modified by Roth and Levin (8) to show the existence of several new compounds between BaO-2.SiO.sub.2 and 2BaO.3SiO.sub.2 in the region labeled as 'solid solutions' in Fig. 3.In the fifties, the condition of immiscibility in borate and silicate systems and its frequent occurrence had been noted by J.
Kracek at the Geophysical Laboratory. Since it was important as a commercial and scientific problem to understand the basic causes of liquid immiscibility, Levin and Block (9, 10) attempted to interpret this phenomenon quantitatively by applying crystal-chemical principles to nineteen binary and eight ternary glass systems. Using ionic radii and one of the two coordination types (for glassformer cations and for modifier cations), they found that the additive density method gives agreement with experimental results in both the borate and silicate systems to within a mole fraction of 5%. The oxygen-volume method agrees to within 2% (mole fraction).In the early sixties, in order to assist the U.S.
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Industry to develop new compositions and search for better property for optical glass, the system La.sub.2O.sub.3-B.sub.3O.sub.3 was studied by Levin et al. (11) by the quenching method. Phases were identified by petrographic microscopy and x-ray diffraction. Three binary compounds were found and no solid solution was encountered in this system. LaBO.sub.3 was of aragonite type with a polymorphic change at 1488 degreesC to a form similar to calcite.
A two-liquid region was found but no solid solution was detected.2.1.3 Properties of Materials for Jewel Instrument BearingsAround the mid-forties, in the course of an investigation on jewel bearings for instruments, conducted under authorization of the Bureau of Aeronautics, United States Navy, NBS made a number of tests and examinations of various materials, included corundum (natural and synthetic), synthetic spinel and glass (12). The natural corundum samples originally were from Montana. Synthetic corundum was prepared by the Verneuil Method.
The properties measured were homogeneity, structural defects, hardness, and strength. It was found that although the corundum has the greatest hardness and strength, its hardness is much greater than that of the usual steel instrument pivots which would cause the pivots to deform or rust. Glass has about the same hardness as the pivots but glass bearings may break under vibration and impact. Spinel is intermediate between corundum and glass in strength and hardness.2.1.4 Battery MaterialsIn the mid-forties, because of World War II, dry cells were put to many new uses involving conditions of extreme heat and cold, and storage over long periods of time. At the request of the Electrochemical Section a study was conducted to characterize a large number of dry battery materials (mainly MnO.sub.2), related synthetic materials and natural minerals (13).
This task showed an early example of combining a number of crystallographic methods, namely, x-ray diffraction (both at room temperature and at elevated temperatures (14) for phase identification and phase transformation studies), DTA for the study of thermal events, and the electron microscope for particle size and surface characterization. MnO.sub.2 was found to lose oxygen at about 600 degreesC and 950 degreesC to bixbyite (MnO.sub.2O.sub.3) and Mn.sub.3O.sub.4 (hausemannite). A reversible polymorphic change from the tetragonal hausemannite to a spinal form was also determined.Related to the work on battery materials, a characterization study was conducted on the phases formed during the discharge of cells. The main Mn-containing phase found after discharge was hetaerolite (ZnMn.sub.2O.sub.4) in which the valence of Mn is 3. A smaller amount of ZnCl.sub.2.4Zn(OH).sub.2 was also found (15,16).2.1.5 Uranium Dioxide with Metal OxidesIn the mid-fifties, investigation of the high-temperature reactions of uranium with a large variety of materials comprised an important segment of the research activities of the U.S.
Atomic Energy Commission and many of its contractors. In the Porcelain and Pottery Section of the NBS, a project for the determination of the phase-equilibrium relations of binary systems containing UO.sub.2 and various metal oxides was carried out by Roth et al. This study also included a critical review of the phase relations at high temperature of UO.sub.2 with 15 other oxides (BeO, MgO, CaO, SrO, BaO, CuO, Al.sub.2O.sub.3, Y.sub.2O.sub.3, Nd.sub.2O.sub.3, SiO.sub.2, ZrO.sub.2, SnO.sub.2, CeO.sub.2, ThO.sub.2, V.sub.2O.sub.5). As part of this work, the technology was developed for ZrO.sub.2 clad VO.sub.2 fuel pellets, used to this day for the fuel rods in all modern nuclear reactors.2.2 Period of 1960s to late 1980sAfter the retirement of H. McMurdie in 1966, the Crystallographic Section of the Ceramics Division was headed by S.
Block, and the Phase Equilibria Section was headed by R. The program of the crystallographic section was divided into several long-term disciplines (18): 1) structure determinations (e.g., a great number of borates and inorganic complexes (19,20)), 2) high pressure (see High Pressure Crystallography), 3) powder diffraction (primarily the determination of standard patterns with the JCPDS-ICDD (see JCPDS-ICDD collaborative program), and 4) the Crystal Data Project (supported by the Standard Reference Data Program) (21).During this period, R. Roth and his co-workers made significant contributions to the phase equilibria and crystal chemistry research of a great variety of important classes of ceramics (over 200 publications today).
Of special note was the paper on the classification of ABO.sub.3 compounds with emphasis on the perovskite structure type phases (22). In order to understand the crystal chemistry of these phases in detail, many single crystals were grown. As crystal growth of the high-temperature oxides was not a straight-forward task due to the high melting temperature and the incongruent melting nature of most oxides in the systems of interest, a low-temperature flux was often used as an aid. Crystallographic investigations were largely carried out involving international collaborations (A.
Stevenson, B. Gatehause, I. Selective studies of the phase equilibria, crystal chemistry and crystallography of important ceramics during this period are summarized belo w.2.2.1 Ferroelectric MaterialsThe viable applications of BaTiO.sub.3 in various fields of industry, including the ferroelectric with the simplest structure, has made this compound a subject of much investigation for many years. Conducted a detailed study of the phase diagram of the BaTiO.sub.3-TiO.sub.2 system, which will be discussed in the section of the dielectric materials (23).
Other Ba-containing materials being studied that are of potential ferroelectric applications systems included Ba.sub.6Nb.sub.28/3Ni.sub.2/3O.sub.30 (24) and (Ba.sub.6-2xR.sub.2x)(Nb.sub.9-xFe.sub.1+x)O.sub.30 (25).Because of the ferroelectric properties of the compound Cd.sub.2Nb.sub.2O.sub.7 below room temperature, the phase equilibria of the CdO-Nb.sub.2O.sub.5 system was of interest (26). Based on the pyrochore type structure of Cd.sub.2Nb.sub.2O.sub.7, Roth has also surveyed the reactions occurring in binary oxide mixtures of the type A.sub.2O.sub.3:2BO.sub.2 as part of the program on ferroelectric ceramics (A = La, Nd, Sm, Gd, Bi, Y, Dy, Yb, In, Sb; B = Ce, U, Ti, Sn, and Zr) (27). On the basis of the existence of the two compounds, La.sub.2O.sub.3.2ZrO.sub.2 and Nd.sub.2O.sub.3.2ZrO.sub.2, the phase diagrams for the systems La.sub.2O.sub.3-ZrO.sub.2 and Nd.sub.2O.sub.3-ZrO.sub.2 were also determined.Another system of interest was PbO-Nb.sub.2O.sub.5 (28) because of the orthorhombic ferroelectric modification phase of PbNb.sub.2O.sub.6 (29); there were contradictory literature reports about the phase transformation of this phase. High-temperature x-ray patterns indicated that pure PbO.Nb.sub.2O.sub.5 has a tetragonal symmetry as a stable modification from the temperature of the high-low phase transformation to the melting point. If the high-temperature modification is cooled quickly from below the transformation point, it will maintain the tetragonal structure in a metastable condition. When it reaches the Curie point of 590 degreesC (30), it transforms metastably and reversibly to the orthorhombic ferroelectric modification.2.2.2 Piezoelectric CeramicsPiezoelectric properties of BaTiO.sub.3 ceramic have simulated a search for other ferroelectrics suitable for fabricating piezoelectric ceramics. Of particular interest was to discover materials having electrical mechanical properties that are stable through a wide range of temperature.
Roth's work in the area of piezoelectric ceramics was extensive. In the mid-fifties, Roth et al. Studied the systems PbZrO.sub.3-PbTiO.sub.3, PbTiO.sub.3-PbO:SnO.sub.2, PbTiO.sub.3-PbZrO.sub.3-PbO:SnO.sub.2, and PbTiO.sub.3-PbHfO.sub.3 (31,32), and discovered the possible desirable properties of compositions near a morphotropic transformation between ferroelectric solid-solution phases. Piezoelectric properties of the lead zirconate-lead titanate solid solution that was discovered in the PbZrO.sub.3-PbTiO.sub.3 system (32), now known as PZT, have made PZT one of the most important advanced electronic ceramic materials known to this day.
This material also revolutionized various industries with its diver se applications.Three series of partial phase diagrams of the Bi.sub.2O.sub.3-MO.sub.x systems (x = 1, M = Ni, Zn, Cd, Mg, Ca, Sr, Ba, Pb; x = 1.5, M = B, Al, Ga, Fe, Mn, Sb, Lu, Sm, La; x = 2, M = Si, Ge, Ti, Sn, Zr, Ce, Te) were determined in order to determine the influence of various foreign cations on the polymorphism of Bi.sub.2O.sub.3 (33,34). As these phases were reported to melt congruently they became ideal candidates for crystal growth.
4 gives an example of the diagram of the Bi.sub.2O.sub.3-SiO.sub.2 system. This study resulted in the development of a sought-after piezoelectric material, SiBi.sub.12O.sub.20, a phase with the largest known rotary inversion of any oxide compound at the time, and is of considerable commercial interest. A structural analysis proved that the phase was noncentrosymmetric. Small tetravalent ions were found to stabilize the cubic body-centered phase.
Body centered cubic bismuth oxide is now believed to be a mixed valence compound with a formula Bi.sup.+5.sub.0.5Bi.sup.+3.sub.12.5O.sub.20. Also found that BaO, SrO, and CaO entered into the solid solution causing an increase in the melting point of Bi.sub.2O.sub.3. This solid solution with apparent rhombohedral symmetry was found to have interesting oxygen ion conductivity.2.2.3 Solid State Ionic ConductorsIn the eighties, there was a significant interest in materials which undergo topotactic insertion of lithium because of their potential use as electrode materials in secondary batteries (35,36). Lithium is ionic in these compounds, and the charge is compensated by a reduction of the host cations. The host structures may be of the layer or framework type. In general, in the framework type structure, Li.sup.+ ions occupy formerly vacant cation sites, and in the layer type structure, they are accommodated in the van der Waals gap between layers.In collaboration with the Bell Telephone Laboratories, two structure types and their derivatives were found to be particularly suitable for lithium insertion reactions, namely, rutile structure (TiO.sub.2) related oxides, and ReO.sub.3 type structure (35,36).
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Ternary Solid Solutions Crystallizing From Ternary Liquids - One Complete Solid Solution System, Two Partial Solid Solution Systems - Crystallization Path - Isothermal and Vertical Sections - V. Solid Solution Systems With Three Phase Equilibria - VI. Solid Solution Systems With Four Phase Equilibria - VII.
Page/Link:Page URL:HTML link:The Free Library. Retrieved Sep 25 2019 fromResearch in phase equilibria and crystallography has been a tradition in the Ceramics Division at National Bureau of Standards/National Institute of Standatrds and Technology (NBS/NIST) since the early thirties. In the early years, effort was concentrated in areas of Portland cement, ceramic glazes and glasses, instrument bearings, and battery materials.
In the past 40 years, a large portion of the work was related to electronic materials, including ferroelectrics, piezoelectrics, ionic conductors, dielectrics, microwave dielectrics, and high-temperature superconductors. As a result of the phase equilibria studies, many new compounds have been discovered. Some of these discoveries have had a significant impact on US industry. Structure determinations of these new phases have often been carried out as a joint effort among NS/NIST colleagues and also with outside collaborators using both single crystal and neutron and x-ray powder diffraction techniques. All phase equilibria diagrams were included in Phase Diag rams for Ceramists. Which are collaborative publications between The American Ceramic Society (ACerS) and NBS/NIST.
All x-ray powder diffraction patterns have been included in the Powder Diffraction File (PDF). This article gives a brief account of the history of the development of the phase equilibria and crystallographic research on ceramic oxides in the Ceramics Division. Represented systems, particularly electronic materials, are highlighted.Key words: ceramic oxides; crystal chemistry; crystallography; electronic materials; historical development; phase equilibria. IntroductionPhase diagrams are critical research tools for many scientific disciplines, including material science, ceramics, geology, physics, metallurgy, chemical engineering, and chemistry.
Phase diagrams can be regarded as \'road maps\' for materials processing. These diagrams contain important information for the development of new materials, control of structure and composition of critical phases, and improvement of properties of technologically important materials. Applications of phase diagrams range from the preparation of high quality single crystals, single-phase bulk materials, deliberate precipitation of second phases, to the formation of melts. Studies of phase equilibria and crystallography of materials are strongly correlated. Crystallographic information is critical for furthering the understanding of phase equilibria, crystal chemistry, physical properties of materials, and performing various theoretical calculations.Phase equlibria and crystallographic research at NBS/NIST has been an important program since the 1930s. Development of new technologies based on ceramic oxides continued to require new materials and new equipment. As a result, a large number of new phases in a diverse area of material science have been discovered and characterized at NBS/NIST.
Methods of structural characterization include single crystal x-ray, powder neutron and x-ray methods, and electron diffraction. Since powder x-ray diffraction patterns are critical for phase identification, patterns of the new phases were also prepared and were included in the Powder Diffraction File (PDF (1)). Throughout these years, NBS/NIST has collaborated with various important ceramic industries, and the systems investigated reflected the changing emphasis of material systems, including cement, glasses, battery materials, dielectrics, ferroelectrics, ionic conductors, superconductors, microwave materials, magnetic materials, and materials for optical application s.In the following, highlights of the phase equilibria and crystallographic research of oxide materials in the Ceramics Division will be followed by more detailed discussions pertaining to the dielectric and superconductor systems.2. Historical Development2.1 The Early Years (1930s to mid 1960s)In the twenties, the Clay and Silicate Product Division at NBS (which later became the Ceramics Division) had seven Sections that were all product-oriented.
Examples of these sections were \'Heavy Clay Products\', \'White Ware\', \'Enamels\', and \'Lime and Gypsum\'. The functions of these Sections were primarily to develop specifications and to perform testing for government agencies. As an example, bricks were tested for water absorption and for resistance to freezing and thawing as a preliminary to writing specifications. The idea of either \'crystallography\' or \'phase equilibria\' of materials was hardly considered. Between the 1930s and mid 1960s, H. McMurdie and his colleagues pioneered the studies of the phase relationships and crystallographic aspects of ceramic materials.
A portion of the study was also conducted in collaboration with both internal and external laboratories. 2.1.1 Portland CementOne of the early phase diagram studies was reported in 1936 on the formation of MgO in the compositions of Portland cement (2). Portland cement clinker consists essentially of lime, alumina, silica, ferric oxide, and magnesia. The last two phases may be generally considered as occurring incidentally, as impurities in the basic raw material.
Since MgO could be harmful in cement, it would be important to determine its behavior in the cement to establish the composition ranges within which MgO appears as a primary phase (the first crystalline phase to appear on cooling a composition from the liquid state). This work was completed primarily by quenching and petrographic microscopy. Figure 1 shows the phase diagram of the CaO-MgO-2CaO.SiO.sub.2-5CaO.3Al.sub.2O.sub.3 system. The surface intersecting the sides of the tetrahedron at A-B-C-D-E-F-G indicates the lower level (4% to 5%) of the primary phase field (the locus of all compositions in a phase diagram having a common primary phase) of MgO. MgO has an exc eptionally large primary phase field.The structural characterization of the products of hydration of Portland cement was carried out by petrographic and powder x-ray techniques (3) with the phases synthesized by hydrothermal methods. The main finding was that the group of compounds Ca.sub.3Al.sub.2Si.sub.3O.sub.12 (andradite), Ca.sub.3Fe.sub.2Si.sub.3O.sub.12 (grossularite), Ca.sub.3Al.sub.3H.sub.12O.sub.12 and Ca.sub.3Fe.sub.2H.sub.12O.sub.12 form a complete series of solid solutions, with a garnet structure. The phases with hydrogen were called hydrogarnets.
All these compounds were found to be cubic with space group Ia 3d.2.1.2 Ceramic Glazes and GlassesIn the thirties, information on phases in the PbO-SiO.sub.2 system was needed in connection with the studies of ceramic glazes and glasses. Four phases were found in this system and their x-ray diffraction patterns were determined by Geller et al. (4), and McMurdie and Bunting (5).
These studies used both x-ray diffraction and petrographic microscopy methods. In addition, x-ray patterns of phases of the K.sub.2O-PbO-SiO.sub.2, PbO-SiO.sub.2, and the Na.sub.2-PbO-SiO.sub.2 systems were prepared in cooperation with the Whiteware Section.In the late forties, phase equilibrium information for the system BaO-B.sub.2O.sub.3-SiO.sub.3 and the subsystem BaOB.sub.2O.sub.3 (6) were of importance to the glass industry as a starting point for the investigations of barium crown glasses (see Fig. These glasses are characterized by high refractive index and low dispersion.
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The experiments included quenchings and the use of differential thermal analysis (DTA). Phases were identified by microscopy and x-ray diffraction. X-ray patterns of four phases including the low form of BaB.sub.2O.sub.4 were reported in the BaO-B.sub.2O.sub.3 system. A two-liquid region (liquid immiscibility) was found. In the ternary system BaOB.sub.2O.sub.3-SiO.sub.2 system (7), one ternary phase, Ba.sub.3B.sub.6Si.sub.2O.sub.16, was discovered and a large two-liquid region was also located (Fig. The system BaO-SiO.sub.2 was later modified by Roth and Levin (8) to show the existence of several new compounds between BaO-2.SiO.sub.2 and 2BaO.3SiO.sub.2 in the region labeled as \'solid solutions\' in Fig. 3.In the fifties, the condition of immiscibility in borate and silicate systems and its frequent occurrence had been noted by J.
Kracek at the Geophysical Laboratory. Since it was important as a commercial and scientific problem to understand the basic causes of liquid immiscibility, Levin and Block (9, 10) attempted to interpret this phenomenon quantitatively by applying crystal-chemical principles to nineteen binary and eight ternary glass systems. Using ionic radii and one of the two coordination types (for glassformer cations and for modifier cations), they found that the additive density method gives agreement with experimental results in both the borate and silicate systems to within a mole fraction of 5%. The oxygen-volume method agrees to within 2% (mole fraction).In the early sixties, in order to assist the U.S.
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Industry to develop new compositions and search for better property for optical glass, the system La.sub.2O.sub.3-B.sub.3O.sub.3 was studied by Levin et al. (11) by the quenching method. Phases were identified by petrographic microscopy and x-ray diffraction. Three binary compounds were found and no solid solution was encountered in this system. LaBO.sub.3 was of aragonite type with a polymorphic change at 1488 degreesC to a form similar to calcite.
A two-liquid region was found but no solid solution was detected.2.1.3 Properties of Materials for Jewel Instrument BearingsAround the mid-forties, in the course of an investigation on jewel bearings for instruments, conducted under authorization of the Bureau of Aeronautics, United States Navy, NBS made a number of tests and examinations of various materials, included corundum (natural and synthetic), synthetic spinel and glass (12). The natural corundum samples originally were from Montana. Synthetic corundum was prepared by the Verneuil Method.
The properties measured were homogeneity, structural defects, hardness, and strength. It was found that although the corundum has the greatest hardness and strength, its hardness is much greater than that of the usual steel instrument pivots which would cause the pivots to deform or rust. Glass has about the same hardness as the pivots but glass bearings may break under vibration and impact. Spinel is intermediate between corundum and glass in strength and hardness.2.1.4 Battery MaterialsIn the mid-forties, because of World War II, dry cells were put to many new uses involving conditions of extreme heat and cold, and storage over long periods of time. At the request of the Electrochemical Section a study was conducted to characterize a large number of dry battery materials (mainly MnO.sub.2), related synthetic materials and natural minerals (13).
This task showed an early example of combining a number of crystallographic methods, namely, x-ray diffraction (both at room temperature and at elevated temperatures (14) for phase identification and phase transformation studies), DTA for the study of thermal events, and the electron microscope for particle size and surface characterization. MnO.sub.2 was found to lose oxygen at about 600 degreesC and 950 degreesC to bixbyite (MnO.sub.2O.sub.3) and Mn.sub.3O.sub.4 (hausemannite). A reversible polymorphic change from the tetragonal hausemannite to a spinal form was also determined.Related to the work on battery materials, a characterization study was conducted on the phases formed during the discharge of cells. The main Mn-containing phase found after discharge was hetaerolite (ZnMn.sub.2O.sub.4) in which the valence of Mn is 3. A smaller amount of ZnCl.sub.2.4Zn(OH).sub.2 was also found (15,16).2.1.5 Uranium Dioxide with Metal OxidesIn the mid-fifties, investigation of the high-temperature reactions of uranium with a large variety of materials comprised an important segment of the research activities of the U.S.
Atomic Energy Commission and many of its contractors. In the Porcelain and Pottery Section of the NBS, a project for the determination of the phase-equilibrium relations of binary systems containing UO.sub.2 and various metal oxides was carried out by Roth et al. This study also included a critical review of the phase relations at high temperature of UO.sub.2 with 15 other oxides (BeO, MgO, CaO, SrO, BaO, CuO, Al.sub.2O.sub.3, Y.sub.2O.sub.3, Nd.sub.2O.sub.3, SiO.sub.2, ZrO.sub.2, SnO.sub.2, CeO.sub.2, ThO.sub.2, V.sub.2O.sub.5). As part of this work, the technology was developed for ZrO.sub.2 clad VO.sub.2 fuel pellets, used to this day for the fuel rods in all modern nuclear reactors.2.2 Period of 1960s to late 1980sAfter the retirement of H. McMurdie in 1966, the Crystallographic Section of the Ceramics Division was headed by S.
Block, and the Phase Equilibria Section was headed by R. The program of the crystallographic section was divided into several long-term disciplines (18): 1) structure determinations (e.g., a great number of borates and inorganic complexes (19,20)), 2) high pressure (see High Pressure Crystallography), 3) powder diffraction (primarily the determination of standard patterns with the JCPDS-ICDD (see JCPDS-ICDD collaborative program), and 4) the Crystal Data Project (supported by the Standard Reference Data Program) (21).During this period, R. Roth and his co-workers made significant contributions to the phase equilibria and crystal chemistry research of a great variety of important classes of ceramics (over 200 publications today).
Of special note was the paper on the classification of ABO.sub.3 compounds with emphasis on the perovskite structure type phases (22). In order to understand the crystal chemistry of these phases in detail, many single crystals were grown. As crystal growth of the high-temperature oxides was not a straight-forward task due to the high melting temperature and the incongruent melting nature of most oxides in the systems of interest, a low-temperature flux was often used as an aid. Crystallographic investigations were largely carried out involving international collaborations (A.
Stevenson, B. Gatehause, I. Selective studies of the phase equilibria, crystal chemistry and crystallography of important ceramics during this period are summarized belo w.2.2.1 Ferroelectric MaterialsThe viable applications of BaTiO.sub.3 in various fields of industry, including the ferroelectric with the simplest structure, has made this compound a subject of much investigation for many years. Conducted a detailed study of the phase diagram of the BaTiO.sub.3-TiO.sub.2 system, which will be discussed in the section of the dielectric materials (23).
Other Ba-containing materials being studied that are of potential ferroelectric applications systems included Ba.sub.6Nb.sub.28/3Ni.sub.2/3O.sub.30 (24) and (Ba.sub.6-2xR.sub.2x)(Nb.sub.9-xFe.sub.1+x)O.sub.30 (25).Because of the ferroelectric properties of the compound Cd.sub.2Nb.sub.2O.sub.7 below room temperature, the phase equilibria of the CdO-Nb.sub.2O.sub.5 system was of interest (26). Based on the pyrochore type structure of Cd.sub.2Nb.sub.2O.sub.7, Roth has also surveyed the reactions occurring in binary oxide mixtures of the type A.sub.2O.sub.3:2BO.sub.2 as part of the program on ferroelectric ceramics (A = La, Nd, Sm, Gd, Bi, Y, Dy, Yb, In, Sb; B = Ce, U, Ti, Sn, and Zr) (27). On the basis of the existence of the two compounds, La.sub.2O.sub.3.2ZrO.sub.2 and Nd.sub.2O.sub.3.2ZrO.sub.2, the phase diagrams for the systems La.sub.2O.sub.3-ZrO.sub.2 and Nd.sub.2O.sub.3-ZrO.sub.2 were also determined.Another system of interest was PbO-Nb.sub.2O.sub.5 (28) because of the orthorhombic ferroelectric modification phase of PbNb.sub.2O.sub.6 (29); there were contradictory literature reports about the phase transformation of this phase. High-temperature x-ray patterns indicated that pure PbO.Nb.sub.2O.sub.5 has a tetragonal symmetry as a stable modification from the temperature of the high-low phase transformation to the melting point. If the high-temperature modification is cooled quickly from below the transformation point, it will maintain the tetragonal structure in a metastable condition. When it reaches the Curie point of 590 degreesC (30), it transforms metastably and reversibly to the orthorhombic ferroelectric modification.2.2.2 Piezoelectric CeramicsPiezoelectric properties of BaTiO.sub.3 ceramic have simulated a search for other ferroelectrics suitable for fabricating piezoelectric ceramics. Of particular interest was to discover materials having electrical mechanical properties that are stable through a wide range of temperature.
Roth\'s work in the area of piezoelectric ceramics was extensive. In the mid-fifties, Roth et al. Studied the systems PbZrO.sub.3-PbTiO.sub.3, PbTiO.sub.3-PbO:SnO.sub.2, PbTiO.sub.3-PbZrO.sub.3-PbO:SnO.sub.2, and PbTiO.sub.3-PbHfO.sub.3 (31,32), and discovered the possible desirable properties of compositions near a morphotropic transformation between ferroelectric solid-solution phases. Piezoelectric properties of the lead zirconate-lead titanate solid solution that was discovered in the PbZrO.sub.3-PbTiO.sub.3 system (32), now known as PZT, have made PZT one of the most important advanced electronic ceramic materials known to this day.
This material also revolutionized various industries with its diver se applications.Three series of partial phase diagrams of the Bi.sub.2O.sub.3-MO.sub.x systems (x = 1, M = Ni, Zn, Cd, Mg, Ca, Sr, Ba, Pb; x = 1.5, M = B, Al, Ga, Fe, Mn, Sb, Lu, Sm, La; x = 2, M = Si, Ge, Ti, Sn, Zr, Ce, Te) were determined in order to determine the influence of various foreign cations on the polymorphism of Bi.sub.2O.sub.3 (33,34). As these phases were reported to melt congruently they became ideal candidates for crystal growth.
4 gives an example of the diagram of the Bi.sub.2O.sub.3-SiO.sub.2 system. This study resulted in the development of a sought-after piezoelectric material, SiBi.sub.12O.sub.20, a phase with the largest known rotary inversion of any oxide compound at the time, and is of considerable commercial interest. A structural analysis proved that the phase was noncentrosymmetric. Small tetravalent ions were found to stabilize the cubic body-centered phase.
Body centered cubic bismuth oxide is now believed to be a mixed valence compound with a formula Bi.sup.+5.sub.0.5Bi.sup.+3.sub.12.5O.sub.20. Also found that BaO, SrO, and CaO entered into the solid solution causing an increase in the melting point of Bi.sub.2O.sub.3. This solid solution with apparent rhombohedral symmetry was found to have interesting oxygen ion conductivity.2.2.3 Solid State Ionic ConductorsIn the eighties, there was a significant interest in materials which undergo topotactic insertion of lithium because of their potential use as electrode materials in secondary batteries (35,36). Lithium is ionic in these compounds, and the charge is compensated by a reduction of the host cations. The host structures may be of the layer or framework type. In general, in the framework type structure, Li.sup.+ ions occupy formerly vacant cation sites, and in the layer type structure, they are accommodated in the van der Waals gap between layers.In collaboration with the Bell Telephone Laboratories, two structure types and their derivatives were found to be particularly suitable for lithium insertion reactions, namely, rutile structure (TiO.sub.2) related oxides, and ReO.sub.3 type structure (35,36).
...'>Phase Equilibria In Ceramics Solution(14.01.2020)Ternary Solid Solutions Crystallizing From Ternary Liquids - One Complete Solid Solution System, Two Partial Solid Solution Systems - Crystallization Path - Isothermal and Vertical Sections - V. Solid Solution Systems With Three Phase Equilibria - VI. Solid Solution Systems With Four Phase Equilibria - VII.
Page/Link:Page URL:HTML link:The Free Library. Retrieved Sep 25 2019 fromResearch in phase equilibria and crystallography has been a tradition in the Ceramics Division at National Bureau of Standards/National Institute of Standatrds and Technology (NBS/NIST) since the early thirties. In the early years, effort was concentrated in areas of Portland cement, ceramic glazes and glasses, instrument bearings, and battery materials.
In the past 40 years, a large portion of the work was related to electronic materials, including ferroelectrics, piezoelectrics, ionic conductors, dielectrics, microwave dielectrics, and high-temperature superconductors. As a result of the phase equilibria studies, many new compounds have been discovered. Some of these discoveries have had a significant impact on US industry. Structure determinations of these new phases have often been carried out as a joint effort among NS/NIST colleagues and also with outside collaborators using both single crystal and neutron and x-ray powder diffraction techniques. All phase equilibria diagrams were included in Phase Diag rams for Ceramists. Which are collaborative publications between The American Ceramic Society (ACerS) and NBS/NIST.
All x-ray powder diffraction patterns have been included in the Powder Diffraction File (PDF). This article gives a brief account of the history of the development of the phase equilibria and crystallographic research on ceramic oxides in the Ceramics Division. Represented systems, particularly electronic materials, are highlighted.Key words: ceramic oxides; crystal chemistry; crystallography; electronic materials; historical development; phase equilibria. IntroductionPhase diagrams are critical research tools for many scientific disciplines, including material science, ceramics, geology, physics, metallurgy, chemical engineering, and chemistry.
Phase diagrams can be regarded as \'road maps\' for materials processing. These diagrams contain important information for the development of new materials, control of structure and composition of critical phases, and improvement of properties of technologically important materials. Applications of phase diagrams range from the preparation of high quality single crystals, single-phase bulk materials, deliberate precipitation of second phases, to the formation of melts. Studies of phase equilibria and crystallography of materials are strongly correlated. Crystallographic information is critical for furthering the understanding of phase equilibria, crystal chemistry, physical properties of materials, and performing various theoretical calculations.Phase equlibria and crystallographic research at NBS/NIST has been an important program since the 1930s. Development of new technologies based on ceramic oxides continued to require new materials and new equipment. As a result, a large number of new phases in a diverse area of material science have been discovered and characterized at NBS/NIST.
Methods of structural characterization include single crystal x-ray, powder neutron and x-ray methods, and electron diffraction. Since powder x-ray diffraction patterns are critical for phase identification, patterns of the new phases were also prepared and were included in the Powder Diffraction File (PDF (1)). Throughout these years, NBS/NIST has collaborated with various important ceramic industries, and the systems investigated reflected the changing emphasis of material systems, including cement, glasses, battery materials, dielectrics, ferroelectrics, ionic conductors, superconductors, microwave materials, magnetic materials, and materials for optical application s.In the following, highlights of the phase equilibria and crystallographic research of oxide materials in the Ceramics Division will be followed by more detailed discussions pertaining to the dielectric and superconductor systems.2. Historical Development2.1 The Early Years (1930s to mid 1960s)In the twenties, the Clay and Silicate Product Division at NBS (which later became the Ceramics Division) had seven Sections that were all product-oriented.
Examples of these sections were \'Heavy Clay Products\', \'White Ware\', \'Enamels\', and \'Lime and Gypsum\'. The functions of these Sections were primarily to develop specifications and to perform testing for government agencies. As an example, bricks were tested for water absorption and for resistance to freezing and thawing as a preliminary to writing specifications. The idea of either \'crystallography\' or \'phase equilibria\' of materials was hardly considered. Between the 1930s and mid 1960s, H. McMurdie and his colleagues pioneered the studies of the phase relationships and crystallographic aspects of ceramic materials.
A portion of the study was also conducted in collaboration with both internal and external laboratories. 2.1.1 Portland CementOne of the early phase diagram studies was reported in 1936 on the formation of MgO in the compositions of Portland cement (2). Portland cement clinker consists essentially of lime, alumina, silica, ferric oxide, and magnesia. The last two phases may be generally considered as occurring incidentally, as impurities in the basic raw material.
Since MgO could be harmful in cement, it would be important to determine its behavior in the cement to establish the composition ranges within which MgO appears as a primary phase (the first crystalline phase to appear on cooling a composition from the liquid state). This work was completed primarily by quenching and petrographic microscopy. Figure 1 shows the phase diagram of the CaO-MgO-2CaO.SiO.sub.2-5CaO.3Al.sub.2O.sub.3 system. The surface intersecting the sides of the tetrahedron at A-B-C-D-E-F-G indicates the lower level (4% to 5%) of the primary phase field (the locus of all compositions in a phase diagram having a common primary phase) of MgO. MgO has an exc eptionally large primary phase field.The structural characterization of the products of hydration of Portland cement was carried out by petrographic and powder x-ray techniques (3) with the phases synthesized by hydrothermal methods. The main finding was that the group of compounds Ca.sub.3Al.sub.2Si.sub.3O.sub.12 (andradite), Ca.sub.3Fe.sub.2Si.sub.3O.sub.12 (grossularite), Ca.sub.3Al.sub.3H.sub.12O.sub.12 and Ca.sub.3Fe.sub.2H.sub.12O.sub.12 form a complete series of solid solutions, with a garnet structure. The phases with hydrogen were called hydrogarnets.
All these compounds were found to be cubic with space group Ia 3d.2.1.2 Ceramic Glazes and GlassesIn the thirties, information on phases in the PbO-SiO.sub.2 system was needed in connection with the studies of ceramic glazes and glasses. Four phases were found in this system and their x-ray diffraction patterns were determined by Geller et al. (4), and McMurdie and Bunting (5).
These studies used both x-ray diffraction and petrographic microscopy methods. In addition, x-ray patterns of phases of the K.sub.2O-PbO-SiO.sub.2, PbO-SiO.sub.2, and the Na.sub.2-PbO-SiO.sub.2 systems were prepared in cooperation with the Whiteware Section.In the late forties, phase equilibrium information for the system BaO-B.sub.2O.sub.3-SiO.sub.3 and the subsystem BaOB.sub.2O.sub.3 (6) were of importance to the glass industry as a starting point for the investigations of barium crown glasses (see Fig. These glasses are characterized by high refractive index and low dispersion.
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The experiments included quenchings and the use of differential thermal analysis (DTA). Phases were identified by microscopy and x-ray diffraction. X-ray patterns of four phases including the low form of BaB.sub.2O.sub.4 were reported in the BaO-B.sub.2O.sub.3 system. A two-liquid region (liquid immiscibility) was found. In the ternary system BaOB.sub.2O.sub.3-SiO.sub.2 system (7), one ternary phase, Ba.sub.3B.sub.6Si.sub.2O.sub.16, was discovered and a large two-liquid region was also located (Fig. The system BaO-SiO.sub.2 was later modified by Roth and Levin (8) to show the existence of several new compounds between BaO-2.SiO.sub.2 and 2BaO.3SiO.sub.2 in the region labeled as \'solid solutions\' in Fig. 3.In the fifties, the condition of immiscibility in borate and silicate systems and its frequent occurrence had been noted by J.
Kracek at the Geophysical Laboratory. Since it was important as a commercial and scientific problem to understand the basic causes of liquid immiscibility, Levin and Block (9, 10) attempted to interpret this phenomenon quantitatively by applying crystal-chemical principles to nineteen binary and eight ternary glass systems. Using ionic radii and one of the two coordination types (for glassformer cations and for modifier cations), they found that the additive density method gives agreement with experimental results in both the borate and silicate systems to within a mole fraction of 5%. The oxygen-volume method agrees to within 2% (mole fraction).In the early sixties, in order to assist the U.S.
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Industry to develop new compositions and search for better property for optical glass, the system La.sub.2O.sub.3-B.sub.3O.sub.3 was studied by Levin et al. (11) by the quenching method. Phases were identified by petrographic microscopy and x-ray diffraction. Three binary compounds were found and no solid solution was encountered in this system. LaBO.sub.3 was of aragonite type with a polymorphic change at 1488 degreesC to a form similar to calcite.
A two-liquid region was found but no solid solution was detected.2.1.3 Properties of Materials for Jewel Instrument BearingsAround the mid-forties, in the course of an investigation on jewel bearings for instruments, conducted under authorization of the Bureau of Aeronautics, United States Navy, NBS made a number of tests and examinations of various materials, included corundum (natural and synthetic), synthetic spinel and glass (12). The natural corundum samples originally were from Montana. Synthetic corundum was prepared by the Verneuil Method.
The properties measured were homogeneity, structural defects, hardness, and strength. It was found that although the corundum has the greatest hardness and strength, its hardness is much greater than that of the usual steel instrument pivots which would cause the pivots to deform or rust. Glass has about the same hardness as the pivots but glass bearings may break under vibration and impact. Spinel is intermediate between corundum and glass in strength and hardness.2.1.4 Battery MaterialsIn the mid-forties, because of World War II, dry cells were put to many new uses involving conditions of extreme heat and cold, and storage over long periods of time. At the request of the Electrochemical Section a study was conducted to characterize a large number of dry battery materials (mainly MnO.sub.2), related synthetic materials and natural minerals (13).
This task showed an early example of combining a number of crystallographic methods, namely, x-ray diffraction (both at room temperature and at elevated temperatures (14) for phase identification and phase transformation studies), DTA for the study of thermal events, and the electron microscope for particle size and surface characterization. MnO.sub.2 was found to lose oxygen at about 600 degreesC and 950 degreesC to bixbyite (MnO.sub.2O.sub.3) and Mn.sub.3O.sub.4 (hausemannite). A reversible polymorphic change from the tetragonal hausemannite to a spinal form was also determined.Related to the work on battery materials, a characterization study was conducted on the phases formed during the discharge of cells. The main Mn-containing phase found after discharge was hetaerolite (ZnMn.sub.2O.sub.4) in which the valence of Mn is 3. A smaller amount of ZnCl.sub.2.4Zn(OH).sub.2 was also found (15,16).2.1.5 Uranium Dioxide with Metal OxidesIn the mid-fifties, investigation of the high-temperature reactions of uranium with a large variety of materials comprised an important segment of the research activities of the U.S.
Atomic Energy Commission and many of its contractors. In the Porcelain and Pottery Section of the NBS, a project for the determination of the phase-equilibrium relations of binary systems containing UO.sub.2 and various metal oxides was carried out by Roth et al. This study also included a critical review of the phase relations at high temperature of UO.sub.2 with 15 other oxides (BeO, MgO, CaO, SrO, BaO, CuO, Al.sub.2O.sub.3, Y.sub.2O.sub.3, Nd.sub.2O.sub.3, SiO.sub.2, ZrO.sub.2, SnO.sub.2, CeO.sub.2, ThO.sub.2, V.sub.2O.sub.5). As part of this work, the technology was developed for ZrO.sub.2 clad VO.sub.2 fuel pellets, used to this day for the fuel rods in all modern nuclear reactors.2.2 Period of 1960s to late 1980sAfter the retirement of H. McMurdie in 1966, the Crystallographic Section of the Ceramics Division was headed by S.
Block, and the Phase Equilibria Section was headed by R. The program of the crystallographic section was divided into several long-term disciplines (18): 1) structure determinations (e.g., a great number of borates and inorganic complexes (19,20)), 2) high pressure (see High Pressure Crystallography), 3) powder diffraction (primarily the determination of standard patterns with the JCPDS-ICDD (see JCPDS-ICDD collaborative program), and 4) the Crystal Data Project (supported by the Standard Reference Data Program) (21).During this period, R. Roth and his co-workers made significant contributions to the phase equilibria and crystal chemistry research of a great variety of important classes of ceramics (over 200 publications today).
Of special note was the paper on the classification of ABO.sub.3 compounds with emphasis on the perovskite structure type phases (22). In order to understand the crystal chemistry of these phases in detail, many single crystals were grown. As crystal growth of the high-temperature oxides was not a straight-forward task due to the high melting temperature and the incongruent melting nature of most oxides in the systems of interest, a low-temperature flux was often used as an aid. Crystallographic investigations were largely carried out involving international collaborations (A.
Stevenson, B. Gatehause, I. Selective studies of the phase equilibria, crystal chemistry and crystallography of important ceramics during this period are summarized belo w.2.2.1 Ferroelectric MaterialsThe viable applications of BaTiO.sub.3 in various fields of industry, including the ferroelectric with the simplest structure, has made this compound a subject of much investigation for many years. Conducted a detailed study of the phase diagram of the BaTiO.sub.3-TiO.sub.2 system, which will be discussed in the section of the dielectric materials (23).
Other Ba-containing materials being studied that are of potential ferroelectric applications systems included Ba.sub.6Nb.sub.28/3Ni.sub.2/3O.sub.30 (24) and (Ba.sub.6-2xR.sub.2x)(Nb.sub.9-xFe.sub.1+x)O.sub.30 (25).Because of the ferroelectric properties of the compound Cd.sub.2Nb.sub.2O.sub.7 below room temperature, the phase equilibria of the CdO-Nb.sub.2O.sub.5 system was of interest (26). Based on the pyrochore type structure of Cd.sub.2Nb.sub.2O.sub.7, Roth has also surveyed the reactions occurring in binary oxide mixtures of the type A.sub.2O.sub.3:2BO.sub.2 as part of the program on ferroelectric ceramics (A = La, Nd, Sm, Gd, Bi, Y, Dy, Yb, In, Sb; B = Ce, U, Ti, Sn, and Zr) (27). On the basis of the existence of the two compounds, La.sub.2O.sub.3.2ZrO.sub.2 and Nd.sub.2O.sub.3.2ZrO.sub.2, the phase diagrams for the systems La.sub.2O.sub.3-ZrO.sub.2 and Nd.sub.2O.sub.3-ZrO.sub.2 were also determined.Another system of interest was PbO-Nb.sub.2O.sub.5 (28) because of the orthorhombic ferroelectric modification phase of PbNb.sub.2O.sub.6 (29); there were contradictory literature reports about the phase transformation of this phase. High-temperature x-ray patterns indicated that pure PbO.Nb.sub.2O.sub.5 has a tetragonal symmetry as a stable modification from the temperature of the high-low phase transformation to the melting point. If the high-temperature modification is cooled quickly from below the transformation point, it will maintain the tetragonal structure in a metastable condition. When it reaches the Curie point of 590 degreesC (30), it transforms metastably and reversibly to the orthorhombic ferroelectric modification.2.2.2 Piezoelectric CeramicsPiezoelectric properties of BaTiO.sub.3 ceramic have simulated a search for other ferroelectrics suitable for fabricating piezoelectric ceramics. Of particular interest was to discover materials having electrical mechanical properties that are stable through a wide range of temperature.
Roth\'s work in the area of piezoelectric ceramics was extensive. In the mid-fifties, Roth et al. Studied the systems PbZrO.sub.3-PbTiO.sub.3, PbTiO.sub.3-PbO:SnO.sub.2, PbTiO.sub.3-PbZrO.sub.3-PbO:SnO.sub.2, and PbTiO.sub.3-PbHfO.sub.3 (31,32), and discovered the possible desirable properties of compositions near a morphotropic transformation between ferroelectric solid-solution phases. Piezoelectric properties of the lead zirconate-lead titanate solid solution that was discovered in the PbZrO.sub.3-PbTiO.sub.3 system (32), now known as PZT, have made PZT one of the most important advanced electronic ceramic materials known to this day.
This material also revolutionized various industries with its diver se applications.Three series of partial phase diagrams of the Bi.sub.2O.sub.3-MO.sub.x systems (x = 1, M = Ni, Zn, Cd, Mg, Ca, Sr, Ba, Pb; x = 1.5, M = B, Al, Ga, Fe, Mn, Sb, Lu, Sm, La; x = 2, M = Si, Ge, Ti, Sn, Zr, Ce, Te) were determined in order to determine the influence of various foreign cations on the polymorphism of Bi.sub.2O.sub.3 (33,34). As these phases were reported to melt congruently they became ideal candidates for crystal growth.
4 gives an example of the diagram of the Bi.sub.2O.sub.3-SiO.sub.2 system. This study resulted in the development of a sought-after piezoelectric material, SiBi.sub.12O.sub.20, a phase with the largest known rotary inversion of any oxide compound at the time, and is of considerable commercial interest. A structural analysis proved that the phase was noncentrosymmetric. Small tetravalent ions were found to stabilize the cubic body-centered phase.
Body centered cubic bismuth oxide is now believed to be a mixed valence compound with a formula Bi.sup.+5.sub.0.5Bi.sup.+3.sub.12.5O.sub.20. Also found that BaO, SrO, and CaO entered into the solid solution causing an increase in the melting point of Bi.sub.2O.sub.3. This solid solution with apparent rhombohedral symmetry was found to have interesting oxygen ion conductivity.2.2.3 Solid State Ionic ConductorsIn the eighties, there was a significant interest in materials which undergo topotactic insertion of lithium because of their potential use as electrode materials in secondary batteries (35,36). Lithium is ionic in these compounds, and the charge is compensated by a reduction of the host cations. The host structures may be of the layer or framework type. In general, in the framework type structure, Li.sup.+ ions occupy formerly vacant cation sites, and in the layer type structure, they are accommodated in the van der Waals gap between layers.In collaboration with the Bell Telephone Laboratories, two structure types and their derivatives were found to be particularly suitable for lithium insertion reactions, namely, rutile structure (TiO.sub.2) related oxides, and ReO.sub.3 type structure (35,36).
...'>Phase Equilibria In Ceramics Solution(14.01.2020)