Phase Equilibria in the System SrO-CdO-V2O5

Phase equilibria in the system SrO-CdO-V₂O₅ in air were established from data obtained by DTA, quenching, and high-temperature solid-state reaction experiments. The SrO-V₂O₅ boundary system contains 4 compounds at SrO to V₂O₅ molar ratios of 4:1, 3:1, 2:1, and 1:1. A fifth compound with a molar composition of ∼10:3 with the apatite crystal structure was also found; it may, however, be a hydroxyapatite phase. The CdO-V₂O₅ system contains the compounds 3CdO·V₂O₅, 2CdO·V₂O₅, and CdO·V₂O₅. The latter compound exhibits a rapid reversible polymorphic transition at 180°C. Complete solid solubility exists in the SrO-CdO system. The most probable compatibility relations were determined from the data available for the SrO-CdO-V₂O₅ ternary system. Limited solid solubility exists between SrO·V₂O₅ and CdO·V₂O₅, and the high-temperature CdO·V₂O₅ polymorph is stabilized to room temperature by solid solution of SrO·V₂O₅. Evidence for the existence of 2 ternary compounds with limited local solid solubility is also presented.     

The Binary System CaO–Nb2O5

The binary system CaO-Nb₂O₅ has been shown to include three compounds: CaO·Nb₂O₅, which melts congruently at 1560°C; 2CaO·Nb₂O₅, which melts congruently at 1576°C; and 3CaO·-Nb₂O₅, which melts incongruently at 1560°C. Three eutectic compositions occur at 6% CaO (1362°C), 23% CaO (1492°C), and 34% CaO (1535°C). These results were obtained by the cone-fusion technique. The compound 3CaO-Nb₂O₅ has been shown to exist in two forms: type I, face-centered cubic with a = 7.978 A, having a superlattice with a = 23.934 A, and type II, orthorhombic (pseudotetragonal, distorted cubic) with a = 11.51 A, b = 11.10 A, c = 15.98 A, having a pseudocell with a = 5.754 A, b = 5.551 A, and c = 7.990 A. The conditions controlling the formation of these two forms were not determinable from the experiments conducted.     

Dielectric Properties of Glasses in the System Nb2O5–Na2O–SiO2

The effect of niobia on the dielectric properties of glasses in the system Nb₂O₅–Na₂O–SiO₂ has been studied from 100 to 10¹⁰ cps. The dielectric constant is high even at frequencies up to 10¹⁰ cps. The Nb⁵⁺ ion, with its small ionic radius and high charge, reinforces the network and raises the dielectric constant.     

Phase Equilibria in the System La2O3-P2O5

Subsolidus phase equilibria in the system La₂O₃-P₂O₅ were established. The system contains six intermediate compounds having molar La₂O₃:P₂O₅ ratios of 3:1,7:3,1:1,1:2,1:3, and 1:5. It was found that the 3:1 compound has a phase transformation at 935°C. The 1:2 compound decomposes to a mixture of 1:1 and 1:3 at 755°C. The 1:3 compound melts incongruently to 1:1 and liquid at 1235°C and the 1:5 compound melts congruently at 1095°C. None of the lanthanum phosphates have lower temperature limits of stability.     

Subsolidus Phase Equilibria in the System Bi2O3-TiO2-Nb2O5

The subsolidus phase equilibria in the system Bi₂O₃-TiO₂-Nb₂O₅ at 1100°C were determined by solid-state reaction techniques and X-ray powder diffraction methods. The system was found to contain 4 ternary compounds, i.e. Bi₃TiNbO₉, Bi₇Ti₄NbO₂₁, a cubic pyrochlore solid solution having a compositional range of 3Bi₂O₃· x TiO₂ (7– x )Nb₂O₅ where x ranges from 2.3 to 6.75, and an unidentified phase, 4Bi₂O₃·11TiO₂·5Nb₂O₅.     

Phase Equilibria in the System Nd2O3-P2O5

The phase diagram for the system NdI₂O₃-P₂O₅ was constructed. Six intermediate compounds, having molar Nd₂O₃: P₂O₅ ratios of 3:1, 7:3, 1:1, 1:2, 1:3, and 1:5, were identified. The 3:1, 7:3, and 1:1 compounds are stable to at least 1500°C. The 1:2 compound decomposes to 1:1 and 1:3 at 730 ± 5°C. The 1:3 and 1:5 compounds melt congruently at 1280 ± 5° and 1055 ± 5°C, respectively. None of the neodymium phosphates show lower temperature limits of stability.     

Phase Equilibria in the System MgO—MgCr2O4

The liquidus, solidus, and subsolidus in the system MgO-MgCrz04 were redetermined. Petro-graphic studies indicated that 47 wt% Cr203 could enter into the periclase lattice at about 235OO C. X-ray and optical data showed that the solid solution decreased to 32 wt% Cr202 at 2165OC, 11 wt% at 1600°C, 5 wt% at 1400°C, 2.5 wt% at 1200°C, and 0 wt% at 1000°C. Petro-graphic studies also suggested that picrochromite could contain about 5 wt% MgO in solid solution. The liquidus was much higher than has been indicated on previously published phase equilibrium diagrams.     

The Binary System Nb2O5— SiO2

The binary system Nb₂O₅— SiO₂ has been shown to include an extensive two-liquid region over the range 5 to 80% Nb₂O₅. The minimum temperature of the two-liquid area is 1695°C. A eutectic composition occurs at 95% Nb₂O₅ and 1448°C. and another at approximately 5% Nb₂O₅ and 1695°C. The experimental results were obtained by the cone-fusion method.     

Phase Equilibria in the System MgO-B2O3

Phase equilibria in the system MgO-B₂O₃ were investigated using DTA and quenching techniques. The system contains 4 invariant points. The compounds MgO·2B₂O₃ and 2MgO·B₂O₃ melt incongruently at 995° and 1312°C, respectively, whereas 3MgO·B₂O₃ melts congruently at 1410°C. A eutectic occurs at 1333°C and 71% MgO.     

Phase Equilibria in the System CaO-Yb2O3

Phase equilibrium relations in the system CaO-Yb₂O₃ were studied. Results of this work demonstrated the existence of four crystalline phases: Yb₂O₃.3CaO, Yb₂O₃.2CaO, Yb₂O₃°CaO, and 2Yb₂O₃°CaO. The 2Yb₂O₃°CaO phase is metastable at all temperatures and was obtained only by rapid quenching from the melt. The crystalline solubility limit of Yb_aO₃ in CaO at 1850°C is slightly greater than 8 mole %, whereas no solubility of CaO in Yb₂O₃ was detected. All four compounds have subsolidus minimums of stability and dissociate into the component oxides below 1800°C. Data are also presented for the systems CaO-Gd₂O₃ and CaO-La₂O₃.     

Subsolidus Phase Equilibria in the System Na2O-Bi2O3-TiO2 at 1000°C

Subsolidus phase relations in the system Na₂O-Bi₂O₃-TiO₂ at 1000°C were investigated by solid-state reaction techniques and X-ray diffraction methods. Five ternary compounds were observed in the system: Na_0.5Bi_4.5Ti₄O₁₅; Na_0.5Bi_0.5TiO₃; a cubic pyrochlore solid solution composed of xNa₂O.25Bi₂O₃.(75−;x) TiO₂ where x is 2.5 to 3.75; a new compound Na_0.5Bi_8.5Ti₇O₂₇ indexed with the orthorhombic cell of a = 5.45, b = 5.42, and c = 36.8 Å; and an unidentified phase with the probable composition NaBiTi₆O₁₄.     

Thermal Expansion of Nb2O5

The high-temperature thermal expansion of monoclinic Nb₂O₅ was studied with X-ray and dilatometric techniques. The X-ray axial thermal expansion was anisotropic; the mean coefficients in the a, b , and c directions, respectively, were 5.3, 0, and 5.9×10⁻⁶°C^-1 from room temperature to 1000°C. It is proposed that this anisotropy causes microcrack formation in sintered polycrystalline samples. The bulk linear thermal expansion of both sintered and hot-pressed samples was determined with a dilatometer from room temperature to 1200°C. A hysteresis effect between heating and cooling data observed for sintered samples was attributed to the occurrence and recombination of internal microcracks.     

Phase Diagram of the System Na2O·Ga2O3-Ga2O3 and its Relation to the System Na2O·Al2O3-Al2O3

A new phase diagram for the system Na₂O-Ga₂O₃ (>50 mol% Ga₂O₃) is presented. It is based on information from differential thermal analysis, X-ray examination of quenched samples, and a radiochemical technique for determining the compositions of a primary phase and a liquid in equilibrium with it. The diagram provides a guide for the growth of primary crystals of the two ionically conducting sodium gallates that are analogs of the technologically important β- and β"-aluminas.     

Formation and Transformation of Solid Solutions in the System Nb2O5–Ta2O5

In the system Nb₂O₅–Ta₂O₅, a continuous series of δ-Nb₂O₅ (δ-Ta₂O₅) solid solutions with a hexagonal cell is formed while heating amorphous materials prepared by the simultaneous hydrolysis of niobium and tantalum alkoxides. The lattice parameters a and c change linearly with increasing Ta₂O₅ content; the former value increases from 0.3604 to 0.3620 nm, and the latter value decreases from 0.3923 to 0.3883 nm. They transform to γ-Nb₂O₅ (β-Ta₂O₅) solid solutions with an orthorhombic cell at higher temperatures. The changes in lattice parameters a and c as functions of composition are the same as those of hexagonal solid solutions, whereas parameter b is relatively constant.     

Oxidation-Reduction Equilibria in Molten Na2O.2SiO2 Glass

The oxidation-reduction equilibria in molten glasses having a soda/silica ratio of 1/2 and containing small amounts of variable-valence ions of the transition elements titanium, vanadium, iron, cobalt, and nickel, the post-transition elements tin and antimony, and the rare-earth element cerium were obtained by equilibrating the melts with various atmospheres. The simple mass expression
was always applicable. In the expression, n is the number of electrons involved in the valence change of the metal M. The value of n is 1 for all systems except for the ions of antimony and tin where n is 2. The ions found are those generally accepted as existing in glass melts which are Ti³⁺, Ti⁴⁺; Fez+, Fe³⁺; Ce³⁺, Ce⁴⁺; Mn²⁺, Mn³; Co²⁺, Co³⁺; Ni²⁺, Ni³; Sb³⁺, Sb⁵⁺; and Sn²⁺, Sn⁴⁺. Two mass action expressions were needed for vanadium-containing glasses to describe the equilibria between 5+, 4+, and 3 f species.     

Phase Equilibria in the Ga2O3In2O3 System

Subsolidus phase relationships in the Ga₂O₃–In₂O₃ system were studied by X-ray diffraction and electron probe microanalysis (EPMA) for the temperature range of 800°–1400°C. The solubility limit of In₂O₃ in the β-gallia structure decreases with increasing temperature from 44.1 ± 0.5 mol% at 1000°C to 41.4 ± 0.5 mol% at 1400°C. The solubility limit of Ga₂O₃ in cubic In₂O₃ increases with temperature from 4.X ± 0.5 mol% at 1000°C to 10.0 ± 0.5 mol% at 1400°C. The previously reported transparent conducting oxide phase in the Ga-In-O system cannot be GaInO₃, which is not stable, but is likely the In-doped β-Ga₂O₃ solid solution.