High-Quartz Solid Solution Phases from Thermally Crystallized Glasses of Compositions Li2O2,MgO).Al2O3,nSiO2

Thermally crystallized glasses of compositions (Li₂,O₂, MgO).Al₂O₃.nSiO₂ were studied by X-ray powder diffraction methods. High-quartz solid solution phases developed at relatively low temperatures and, for n 3.5, transformed at higher temperatures to keatite solid solution phases. Associated phases, if present, were Mg spinel and/or cordierite, or a few other trace phases. The a crystallographic axis (a₀) of high-quartz solid solutions decreased with increase of MgO and/or SiO₂. The c crystallographic axis (c₀) decreased with increasing MgO; it also decreased with increasing SiO₂, but only when MgO content was low. X-ray diffraction photographs of single crystals of high-quartz solid solutions of compositions LiaO.Al₂O₃.nSiO₃ demonstrated that the maintenance of a basic high-quartz structure is the basis of the solid solution relation. Three modifications of the high-quartz structure were recognized in the Li₂O-Al₂O₃−SiO₃ system. These modifications were based on the occurrence and positions of superlattice reflections. The high-quartz solid solution from Li₂O Al₂O₃−2SiO₂, showing streaky reflections in its precession photographs, suggested a defective structure. The term "high-quartz solid solution," with or without additional prefixes specifying the compositional series and modification, was considered the preferred nomenclature for these solid solution phases.     

The System Al2O3-Cr2O3-Sio2

Liquidus phase equilibrium data are presented for the system Al₂O₃-Cr₂O₃-SiO₂. The liquidus diagram is dominated by a large, high-temperature, two-liquid region overlying the primary phase field of corundum solid solution. Other important features are a narrow field for mullite solid solution, a very small cristobalite field, and a ternary eutectic at 1580°C. The eutectic liquid (6Al₂O₃-ICr₂O₃-93SiO₂) coexists with a mullite solid solution (61Al₂O₃-10Cr₂O₃-29SiO₂), a corundum solid solution (19Al₂O₃-81Cr₂O₃), and cristobalite (SO₂). Diagrams are presented to show courses of fractional crystallization, courses of equilibrium crystallization, and phase relations on isothermal planes at 1800°, 1700°, and 1575°C. Tie lines were sketched to indicate the composition of coexisting mullite and corundum solid solution phases.     

Phase Relations in the System ZrO2-Y2O3 at Low Y2O3 Contents

Subsolidus phase relations in the low-Y₂O₃ portion of the system ZrO_2-Y₂O₃ were studied using DTA with fired samples and X-ray phase identification and lattice parameter techniques with quenched samples. Approximately 1.5% Y₂O₃ is soluble in monoclinic ZrO₂, a two-phase monoclinic solid solution plus cubic solid solution region exists to ∼7.5% Y₂O₃ below ∼500°C, and a two-phase tetragonal solid solution plus cubic solid solution exists from ∼1.5 to 7.5% Y₂O₃ from ∼500° to ∼1600°C. At higher Y₂O₃ compositions, cubic ZrO₂ solid solution occurs.     

Subsolidus Phase Equilibria and Ordering in the System ZrO2-Y2O3

The subsolidus phase relations in the entire system ZrO₂-Y₂O₃ were established using DTA, expansion measurements, and room- and high-temperature X-ray diffraction. Three eutectoid reactions were found in the system: ( a ) tetragonal zirconia solid solution→monoclinic zirconia solid solution+cubic zirconia solid solution at 4.5 mol% Y₂O₃ and ∼490°C, ( b ) cubic zirconia solid solutiow→δ-phase Y₄Zr₃O₁₂+hexagonalphase Y₆ZrO₁₁ at 45 mol% Y₂O₃ and ∼1325°±25°C, and ( c ) yttria C -type solid solution→wcubic zirconia solid solution+ hexagonal phase Y₆ZrO₁₁ at ∼72 mol% Y₂O₃ and 1650°±50°C. Two ordered phases were also found in the system, one at 40 mol% Y₂O₃ with ideal formula Y₄Zr₃O₁₂, and another, a new hexagonal phase, at 75 mol% Y₂O₃ with formula Y₆ZrO₁₁. They decompose at 1375° and >1750°C into cubic zirconia solid solution and yttria C -type solid solution, respectively. The extent of the cubic zirconia and yttria C -type solid solution fields was also redetermined. By incorporating the known tetragonal-cubic zirconia transition temperature and the liquidus temperatures in the system, a new tentative phase diagram is given for the system ZrO₂-Y₂O₃.     

Synthesis of γ-Ga2O3–Al2O3 Solid Solutions by the Glycothermal Method

The reaction of mixtures of aluminum isopropoxide and gallium acetylacetonate in 1,4-butanediol or 1,5-pentanediol at high temperatures (glycothermal reaction) directly gave the γ-Ga₂O₃–Al₂O₃ solid solutions, which had high catalytic activities for selective reduction of NO using methane as the reducing agent. However, the reaction with a higher Al/(Ga+Al) charged ratio yielded the glycol derivative of boehmite as a by-product and the catalytic activity of the solid solution decreased. Therefore, synthesis of the solid solution using various glycols was examined and it was found that solid solutions with high Al contents without contamination of the glycol derivative of boehmite were obtained by using 1,6-hexanediol as a reaction medium. The solid solution exhibited a higher NO conversion than that synthesized in other glycols.     

X-Ray Study of the Solid Solution of TiO, Fe2O3, and G, O3 in Mullite (3A12O3a2Si02)

A study of the solid solution of TiO₂, Fe₂O₃, and Cr₂0₃ in mullite was made by measuring the changes in lattice parameters and unit-cell volume. Synthetic mullite (3O₃-2SiO₂) was reacted with up to 12 weight % of the oxides at temperatures ranging from 1000° to 17000C. The approximate minimum temperature required for the formation of solid solution was 12000C. for Fe₂0₃ and 1400°C. for Cr₂O₃ and TiO₃. The maximum amount of solid solution found was 2 to 4% TiO₂ at 1600°C., 10 to 12% Fe₂O_s at 1300°C., and 8 to 10% Cr_ZO₃ at 1600OC. Lattice parameters and unit-cell volumes for each solid solution series increased with increasing amounts of foreign oxide. There was good agreement between the calculated and observed increase in cell dimensions for the iron oxide series. Except in the case of titania, there was good agreement between X-ray data and petrographic observations.     

Activity-Composition Relations in Co2SiO4-Fe2SiO4 Solid Solutions at 1180°C

Activity-composition relations of cobalt orthosilicate in cobalt-iron-orthosilicate solid solutions were determined at 1180°C by studying the equilibrium between these solid solutions, silica, metallic cobalt, and a gas phase of known oxygen pressures. The solution shows a slight positive deviation from ideality.     

The System MgO–MgAl2O4

In the determination of the liquidus, solidus, and subsolidus of the system MgO-MgAl₂O₄ the limits of the solid solution of A1 ions in periclase and Mg ions in spinel were measured. By using both X-ray diffraction and optical techniques, the maximum periclase solid solution was found at 82 wt% MgO, 18 wt% A12O3 (9.5% A1³⁺) and maximum spinel solid solution at 39% MgO, 61 % A1203 (6% Mg⁺⁺). Periclase and spinel solid solutions existed stably in easily detectable amounts at temperatures above approximately 1500°C.     

The Systems BaO-SrO-TiO2, BaO-CaO-TiO2, and SrO-CaO-TiO2

The solid phases formed at 1400°C. in air in the three-component systems BaO-SrO-TiO₂, BaO-CaO-TiO₂, and SrO-CaO-TiO₂ are described. Besides solid solutions of components with known structures, some new ternary compounds have been studied. The dielectric constants and loss factors of a number of specimens are given. Crystallographic data of the compounds BaCaTiO₄, Ba₃Ca₂Ti₂O₉, and Ca₃Ti₂O₇ and of the solid solution series (Ba, Sr), TiO₄ are presented. The preparation of the new compounds is described in detail.     

Solid-Liquid Equilibria in the System Si3N4-AlN-Si02-A12O3

Solid-liquid equilibria at 1750°C and subsolidus phase relations in the system Si₃N₄−AlN-SiO₂−Al₂O₃ were determined for the composition region bounded by the β-Si₃N₄ solid solution line and silica-alumina join X-ray diffraction and optical microscopy were used to determine the phases present in specimens cooled rapidly after equilibration. The extent of a single liquid-phase region and the tie lines for the βsolid solution + liquid field at 1750°C were established from quantitative X-ray diffractometry and lattice parameter measurements of βsolid solutions in equilibrium with liquid. The results were corroborated by optical microscopy and melting behavior observations. A new composition, Si₁₂Al₁₈O₃9N₈, is suggested for the x₁ phase. The lowest melting temperature in the system is ≅ 1480°C and the corresponding composition is 10 eq% Al-90 eq%O.     

Solid Solution and Chromium Oxide Loss in Part of the System MgO-Al2O3-Cr2O3-SiO2

Thermal and X-ray studies show that there is complete solid solution between MgO.Cr₂O₃ and MgO.Al₂O₃ and that the spinel solid solutions are stable with no exsolution down to temperatures as low as 510°C. There is no solid solution of excess Cr₂O₃ in MgO.Cr₂O₃ nor of MgO.Cr₂O₃ in Cr₂O₃. The join MgO.Cr₂O₃–Al₂O₃ is found to be nonbinary; compositions along that join yield mixtures of a chromium oxide-alumina solid solution and a spinel solid solution on firing to temperatures high enough to promote solid-state reaction. Chromium oxide loss by volatilization increases at higher temperature. At a given temperature, chromium oxide loss is found to vary directly with the partial pressure of oxygen in the furnace atmosphere and with the ratio of MgO to SiO₂ in the charges heated.     

The System MgO-Cr2O3−Fe2O3 at 1300°c in Air

Phase relations in air at 1300°C were determined for the system MgO-Cr₂O₃−Fe₂O₃ by conventional quenching techniques. Details of the phase equilibria were established for: (1) the sesquioxide solid solution between Cr₂O₃ and Fe₂O₃, (2) the spinel solid solution field between MgCr₂O₄ and MgFe₂O₄, and (3) the periclase solid solution field for MgO. Selected tie lines connecting coexisting compositions were established with X-ray diffractometer data. Diffuse reflectance spectra, diffractometer intensity ratios, and lattice parameter measurements were obtained for quenched samples to study the structural inversion in the spinel series MgCr₂O4-MgFe₂O₄.     

Electrical, X-Ray, and Thermal Expansion Studies in the System KNbO3-AgNbO3

Unlike the KNbO₃-NaNbO₃ system, the KNbO₃-AgNbO₃ system possessed a very limited degree of solid solution between its end-members. Solid solution of AgNbO₃ in KNbO₃ was limited to slightly less than 6 mole %, and solid solution of KNbO₃ in AgNbO₃ was limited to less than 0.5 mole %. Because of a tendency for the K_{1- x} Ag _x NbO₃ system to lose oxygen spontaneously during firing when 0.06 ≤ x ≤ 0.995, the system could not be treated as a true binary system. The compositions in the KNbO₃ solid solution region (0 ≤ x < 0.06) were ferroelectric at room temperature. Lattice parameter, relative permittivity, and thermal expansion measurements were made on specimens in the region 0 ≤ x ≤ 0.06.     

Thermodynamic Modeling of the Isomorphous Phase Diagrams in the Al2O3–Cr2O3 and V2O3–Cr2O3 Systems

The phase diagrams in the Al₂O₃–Cr₂O₃ and V₂O₃–Cr₂O₃ systems have been assessed by thermodynamic modeling with existing data from the literature. While the regular and subregular solution models were used in the Al₂O₃–Cr₂O₃ system to represent the Gibbs free energies of the liquid and solid phases, respectively, the regular solution model was applied to both phases in the V₂O₃–Cr₂O₃ system. By using the liquidus, solidus, and/or miscibility gap data, the interaction parameters of the liquid and solid phases were optimized through a multiple linear regression method. The phase diagrams calculated from these models are in good agreement with experimental data. Also, the solid miscibility gap and chemical spinodal in the V₂O₃–Cr₂O₃ system were estimated.     

Effect of Nd2O3 Concentration on the Defect Structure of CeO2–Nd2O3 Solid Solution

An extensive X-ray study of CeO₂–Nd₂O₃ solid solutions was performed, and the densities of solid solutions containing various concentrations of NdO_1.5 were measured using several techniques. Solid solutions containing 0–80 mol% NdO_1.5 were synthesized by coprecipitation from Ce(NO₃)₃ and Nd(NO₃)₃ aqueous solutions, and the coprecipitated samples were sintered at 1400°C. A fluorite structure was observed for CeO₂–NdO_1.5 solid solutions with 0–40 mol% NdO_1.5, which changed to a rare earth C-type structure at 45–75 mol% NdO_1.5. The change in the lattice parameters of CeO₂–NdO_1.5 solid solutions, when plotted with respect to the NdO_1.5 concentration, showed that the lattice parameters followed Vegard's law in both the fluorite and rare earth C-type regions. The maximum solubility limit for NdO_1.5 in CeO₂ solid solution was approximately 75 mol%. The relationship between the density and the Nd concentration indicated that the defect structure followed the anion vacancy model over the entire range (0–70 mol% NdO_1.5) of solid solution.     

Phase Relations in the System UO2-UO3– Y2O3

The phase relations in the system U02-U03-Yz03, particularly in the Y203-rich region, were examined by X-ray and chemical analyses of reacted powders heated at temperatures up to 1700°C in H₂, CO₂-CO₂ and air. Four phases were identified in the system at temperatures between 1000° and 1700°C: U308, face-centered cubic solid solution, body-centered cubic solid solution, and a rhombohedral phase of composition (U,Y)₇O₂ ranging from 52.5 to 75 mole % Y₂O₃. The rhombohedral phase oxidized to a second rhombohedral phase with a nominal composition (U,Y), at temperatures below 1000°C. This phase transformed to a face-centered cubic phase after heating in air above 1000° C. The solubility of UO, in the body-centered cubic phase is about 14 mole % between 1000° and 1700°C but decreases to zero as the uranium approaches the hexavalent oxidation state. The solubility of Yz03 in the face-centered cubic solid solution ranges from 0 to 50 mole % Y2O3 under reducing conditions and from 33 to 60 mole % Y2O3 under oxidizing conditions at 1000°C. At temperatures above 1000° C, the face-centered cubic solid solution is limited by a filled fluorite lattice of composition (U,Y)O₂. For low-yttria content, oxidation at low temperatures (<300°C) permits additional oxygen to be retained in the structure to a composition approaching (U,Y)O_2.25 A tentative ternary phase diagram for the system UO₂-UO₃-Y₂O₃ is presented and the change in lattice parameter and in cell volume for the solid-solution phases is correlated with the composition.     

Inclusions of Nanometer-Sized Al2O3 Particles in a Crystalline (Sc,Lu)2(WO4)3 Matrix

Nanometer-sized Al₂O₃ particles were successfully synthesized as crystalline inclusions by mixing both components to form the nanometer-sized particles and the (Sc,Lu)₂(WO₄)₃ matrices in a crystal lattice by preparing a solid solution of (Sc,Lu)₂(WO₄)₃ and Al₂(MoO₄)₃ and then decomposing the solid solution. The particles were dispersed uniformly and without agglomeration, which is commonly observed with conventional preparation techniques. The average particle size of the Al₂O₃ was 3.5 nm, and the standard deviation was estimated to be 1.1 nm.     

High-Temperature Electrical Properties of the Bi2.1Sr1.9(Ca1–xYx)Cu2Oy Solid Solution

By a combination of conventional physical property measurements and high-temperature electrical property studies, the solid solution limit, transport parameters, and potential defect regimes of the Bi_2.1Sr_1.9(Ca_{1 - x} Y _x )Cu₂O _y solid solution were established. A continuous solid solution extends to x = 0.7 or 0.8. The electrical properties indicate that the product of the hole density-of-states and mobility for semiconducting compositions is approximately an order of magnitude smaller than for the other p -type superconducting cuprates. A pronounced drop in hole concentration accompanies the tetragonal-to-orthorhombic transition at x = 0.5, whereafter superconductivity disappears. The electrical properties also indicate that a composition x change occurred reversibly below 1100°C.     

The System Manganese Oxide–Cr2O3 in Air

The quenching technique has been used to determine equilibrium relations in the system manganese oxide-Cr₂O₃ in air in the temperature range 600° to 1980°C. The following isobaric invariant situations have been determined: At 910°± 5°C tetragonal Mn₃O₄ solid solution, cubic Mn₃O₄ solid solution (=spinel), Mn₂O₃ solid solution, and gas coexist in equilibrium. Cubic Mn₃O₄ solid solution, Cr₂O₃ solid solution, liquid, and gas are present together in equilibrium at 1970°± 20°C. The invariant situation at which cubic Mn₃O₄ solid solution, Mn₂O₃ solid solution, Cr₂O₃ solid solution, and gas exist together in equilibrium is below 600°C.     

Reactions in the System Li2O–MgO–Al2O3–SiO2: I, The Cordierite-Spodumene Join

Phase equilibria along the nonbinary join between cordierite (2MgO · 2Al₂O₃· 5SiO₂) and spodumene (Li₂O · Al₂O₃· 4SiO₂) were investigated in the temperature range 800° to 1550°C. using the quench technique on fourteen compositions. The phase diagram at high temperatures is characterized by a very small region of solid solution on the cordierite side, appreciable solid solution on the spodumene side, and regions of three and four phases toward the center of the system, including liquid, α-cordierite, mullite, spinel, corundum, and β-spodumene and its solid solutions. The liquidus has a flat minimum between 40 and 50% cordierite at 1347°, and rises on one side to the congruent melting point of β-spodumene (1421°) and on the other side to the temperature of complete melting of cordierite (1530°). The lowest temperature at which liquid appears is 1325°. At low temperatures a complete series of metastable solid solutions exists between μ-cordierite and β-spodumene. The significance of the data in the preparation of thermal-shock-resisting bodies is discussed.