Quaternary Compounds Prepared in a CaO–Y2O3–SnO2 System

Compounds in a CaO–Y₂O₃–SnO₂ system were prepared by a solid-state reaction at 1673 K. The phase relation in this system was investigated by powder X-ray diffraction. Besides the previously reported ternary compounds, CaSnO₃, Ca₂SnO₄, Y₂Sn₂O₇, and a quaternary compound Ca_0.4Y_1.2Sn_0.4O₃, solid-solution series of Ca_{2− x} Y_{2 x} Sn_{1− x} O₄ with 0≤ x ≤0.5, and Ca_{1− y} Y_{2 y} Sn_{1− y} O₃ with 0≤ y ≤0.2 and 0.95≤ y ≤1.0 were found. The cell parameters of these solid-solution series were refined. The changes of rhombohedral cell parameters in the samples prepared in the range 0.565< y <0.714 of Ca_{1− y} Y_{2 y} Sn_{1− y} O₃ suggested the existence of solid solutions of Ca_0.4Y_1.2Sn_0.4O₃, although their single phases could not be prepared, except at y =0.6.     

Phase Diagram and Oxygen-Ion Conductivity in the Y2O3-Nb2O5 System

The phase equilibria in the Y₂O₃-Nb₂O₅ system have been studied at temperatures of 1500° and 1700°C in the compositional region of 0-50 mol% Nb₂O₅. The solubility limits of the C-type Y₂O₃ cubic phase and the YNbO₄ monoclinic phase are 2.5 (±1.0) mol% Nb₂O₅ and 0.2 (±0.4) mol% Y₂O₃, respectively, at 1700°C. The fluorite (F) single phase exists in the region of 20.1-27.7 mol% Nb₂O₅ at 1700°C, and in the region of 21.1-27.0 mol% Nb₂O₅ at 1500°C, respectively. Conductivity of the Y₂O₃- x mol% Nb₂O₅ system increases as the value of x increases, to a maximum at x = 20 in the compositional region of 0 ≤ x ≤ 20, as a result of the increase in the fraction of F phase. In the F single-phase region, the conductivity decreases in the region of 20-25 mol% Nb₂O₅, because of the decrease in the content of oxygen vacancies, whereas the conductivity at x = 27 is larger than that at x = 25. The conductivity decreases as the value of x increases in the region of 27.5 ≤ x ≤ 50, because of the decrease in the fraction of F. The 20 mol% Nb₂O₅ sample exhibits the highest conductivity and a very wide range of ionic domain, at least up to log p _O2=−20 (where p _O2 is given in units of atm), which indicates practical usefulness as an ionic conductor.     

Phase Relations and Ordering in the Systems MgO-Y2O3-ZrO2 and CaO-MgO-ZrO2

The phase relations in the systems MgO-Y₂O₃-ZrO₂ and CaO-MgO-ZrO₂ were established at 1220° and 1420°C. The system MgO-Y₂O₃-ZrO₂ possesses a much-larger cubic ZrO₂ solid solution phase field than the system CaO-MgO-ZrO₂ at both temperatures. The ordered δ phase (Zr₃Y₄O₁₂) was found to be stable in the system ZrO₂-Y₂O₃ at 1220°C. Two ordered phases φ₁ (CaZr₄O₉) and φ₂ (Ca₆Zr₁₉O₄₄) were stable at 1220°C in the system ZrO₂-CaO. At 1420°C no ordered phase appears in either system, in agreement with the previously determined temperature limits of the stability for the δ, φ₁, and φ₂ phases. The existence of the compound Mg₃Y_zO₆ could not be confirmed.     

Subsolidus Phase Equilibria of the CaO-B2O3-BaO System

The "subsolidus" phase relations at room temperature in the system CaO-B₂O₃-BaO are investigated. Specimens of various compositions were prepared from appropriate ratios of CaCO₃, B₂O₃, and BaCO₃, and fired from 780° to 1040°C according to their melting points. There are three ternary compounds in this system. The crystal structures of these compounds were determined by X-ray diffraction (XRD). CaBa₂(BO₃)₂ and Ca₅Ba₂B₁₀O₂₂ are monoclinic structures. The lattice constants a = 14.221 Å, b = 4.569 Å, c = 11.926 A, β= 99.947°, and V = 763.4 å³ for CaBa₂(BO₃)₂ and a = 15.714 å, b = 6.184 å, c = 10.204 å, β= 93.954°, and V = 989.29 å₃ for Ca₅Ba₂B₁₀O₂₂ are obtained. The third compound, CaBa₂(B₃O₆)₂, is isostructural with the high form of BaB₂O₄ with lattice constants a = 7.167 å and c = 35.298 å. Powder second harmonic generation efficiencies of these ternary compounds were measured using a homemade apparatus.     

Pyrochlore Phases in the System ZnO–Bi2O3–Sb2O5: I. Stoichiometries and Phase Equilibria

Two cubic pyrochlore phases exist in the system ZnO–Bi₂O₃–Sb₂O₅. Neither has the supposed "ideal" stoichiometry, Zn₂Bi₃Sb₃O₁₄. One, P ₁, is a solid solution phase, Zn_{2+ x} Bi_{2.96−( x − y )}Sb_{3.04− y} O_14.04+δ where 0< x <0.13(1), 0< y <0.017(2) and a =10.4285(9)−10.451(1) Å. The other, P ₂, is a line phase, Zn₂Bi_3.08Sb_2.92O_13.92 with a =10.462(2) Å. Subsolidus phase relations at 950°C involving phases P ₁ and P ₂ in the ZnO–Bi₂O₃–Sb₂O₅ phase diagram have been determined.     

Phase Relations in the System Bi2O3-WO3

Phase relations in the system Bi₂O₃-WO₃ were studied from 500° to 1100°C. Four intermediate phases, 7Bi₂O₃· WO₃, 7Bi₂O₃· 2WO₃, Bi₂O₃· WO₃, and Bi₂O₃· 2WO₃, were found. The 7B₂O · WO₃ phase is tetragonal with a ₀= 5.52 Å and c ₀= 17.39 Å and transforms to the fcc structure at 784°C; 7Bi₂O₃· 2WO₃ has the fcc structure and forms an extensive range of solid solutions in the system. Both Bi₂O₃· WO₃ and Bi₂O₃· 2WO₃ are orthorhombic with (in Å) a ₀= 5.45, b ₀=5.46, c ₀= 16.42 and a ₀= 5.42, b ₀= 5.41, c ₀= 23.7, respectively. Two eutectic points and one peritectic exist in the system at, respectively, 905°± 3°C and 64 mol% WO₃, 907°± 3°C and 70 mol% WO₃, and 965°± 5°C and 10 mol% WO₃.     

Ferroelectric and Structural Properties of the Pb(Sc1/2Nb1/2)1-x,Tix,O3 System

Extensive solid solution was observed in the system Pb(Sc_1/2/,Nb_1/2,)_1-x,Ti_x,O₃. In the range 0 ≤ x ≤ 0.425 a rhombohedral ferroelectric phase was stable at 25° C. In the range 0.45 ≤ x ≤ 1.00 a tetragonal ferroelectric phase was stable at this temperature. The phase diagram of the system below 500° C strongly resembles that of PbZrO₃−PbTiO₃. The compound Pb(Sc_1/2Nb_1/2)O₃ exhibited rhombohedral perovskite cell symmetry below the ferroelectric ↔ paraelectric transition temperature, and the angle a was acute. The radial coupling coefficient was 0.46 for the composition Sc_1/2Nb_1/2)_0.575Ti_0.4250O₃. At 25°C this composition consisted primarily of the rhombohedral phase with a small amount of the tetragonal phase present. The ferroelectric ↔ paraelectric transition occurred over a temperature range in the rhombohedral phase field. The spontaneous polarization was finite at temperatures considerably above the temperature of the permittivity maximum for a given rhombohedral solid solution.     

Studies in Lithium Oxide Systems: XII, Li2O-B2O3-Al2O3

Tentative phase relations in the binary system BnOa-A1₂O₃ are presented as a prerequisite to the understanding of the system Li₂O-B₂O₃-Al₂O₃. Two binary compounds, 2A1₂O₃.B₂O₃ and 9A1₂O₃.-2B₂O₃, melted incongruently at 1030° f 7°C and about 144°C, respectively. Two ternary compounds were isolated, 2Li₂O.A1₂O₃.B₂O₃ and 2Li₂O. 2AI₂O₃. 3B₂0₃. The 2:1:1 compound gave a melting reaction by differential thermal analysis at 870°± 20° C, but the exact nature of the melting behavior was not determined. The 2:2:-3 compound melted at 790°± 20° C to Li_zO.-5Al₂O₃ and liquid. X-ray diffraction data for the compounds are presented and compatibility triangles are shown.     

Subsolidus Phase Relationships in the Ga2O3–Al2O3–TiO2 System

Subsolidus phase relationships in the Ga₂O₃–Al₂O₃–TiO₂ system at 1400°C were studied using X-ray diffraction. Phases present in the pseudoternary system include TiO₂ (rutile), Ga_{2−2 x} Al_{2 x} O₃ ( x ≤0.78 β-gallia structure), Al_{2−2 y} Ga_{2 y} O₃ ( y ≤0.12 corundum structure), Ga_{2−2 x} Al_{2 x} TiO₅ (0≤ x ≤1 pseudobrookite structure), and several β-gallia rutile intergrowths that can be expressed as Ga_{4−4 x} Al_{4 x} Ti _{n −4}O_{2 n −2} ( x ≤0.3, 15≤ n ≤33). This study showed no evidence to confirm that aluminum substitution of gallium stabilizes the n =7 β-gallia–rutile intergrowth as has been mentioned in previous work.     

Phase Equilibria of the La2O3-SrO-CuO System at 950°C and 10 kbar

Phase equilibria of the La₂O₃-SrO-CuO system have been determined at 950°C and 10 kbar (1 GPa). Stable phases at the apices of the ternary phase diagram are CuO, La₂O₃, and SrO. Stable intermediate phases are La₂CuO₄ in the LaO_1.5-CuO binary and Sr₂CuO₃, SrCuO₂, and Sr₁₄Cu₂₄O₄₁ in the CuO-SrO binary. The La_2-xSr _x CuO_4-δ solid solution is stable where 0.0 ≤ x ≤ 1.3, the La_2-xSr_1+xCu₂O_6+δ solid solution is stable where 0.0 ≤ x ≤ 0.2, the La_8-xSr _x Cu₈O_20-δ solid solution is stable where 1.3 ≤ x ≤ 2.7, the La _x Sr_14-x-Cu₂₄O₄₁ solid solution is stable where 0 ≤ x ≤ 6, and the La_1+xSr_2-xCu₂O_5.5+δ phase is stable where 0.04 ≤ x ≤ 0.16. The La₂O₃-SrO-CuO phase diagram at 950°C and 10 kbar is almost identical to that determined by other authors at 950°C and 1 atm, in terms of phase stability and solid-solution ranges.     

Phase Equilibrium Studies in the System CaO-Cr2O3-SiO2

Results are presented of a study in air of mixtures in the system CaO-Cr₂O₃-SiO₂. The phase equilibrium diagram shows relations at liquidus temperatures for all but the high-lime part of the system. In this omitted part chromium in the mixtures oxidizes in air to higher valence forms. The compound Ca₃Cr₂Si₃O₁₂ (uvarovite) occurs at subsolidus temperatures, decomposing at 1370°C. to α-CaSiO₃ and Cr₂O₃. The inhibiting action of chromium oxide on the inversion of high-temperature forms of Ca₂SiO₄ to the low-temperature γ-Ca₂SiO₄ is discussed in the light of new data. Evidence is presented for the existence of a pentavalent chromium compound, Ca₃(CrO₄)₂, having solid-solution relations with Ca₃SiO₄.     

Crystal Chemistry and Phase Transitions in Substituted Pollucites along the CsAlSi2O6-CsTiSi2O6.5 Join: A Powder Synchrotron X-ray Diffractometry Study

The crystal structures for a suite of substituted pollucites with the compositions CsTi _x Al_{1– x} Si₂O_{6+0.5 x} , 0 ≤ x ≤ 1, have been determined from Rietveld analysis of powder synchrotron XRD data. Our results indicate that the pollucite end member (CsAlSi₂O₆) has a tetragonal structure (space group I 4₁/ a ), whereas all other compositions are cubic (space group Ia 3 d ). The increased symmetry for the titanium-substituted structures is presumably due to the incorporation of additional O²⁻ anions (needed for compensating the charge imbalance between Ti⁴⁺ and Al³⁺), which effectively holds open the expanded cubic framework. In situ cooling experiments of the substituted phase CsTi_0.1Al_0.9Si₂O_6.05 reveal a displacive transformation to the tetragonal structure at ∼230 K. This transformation is tricritical in nature and is analogous to the tetragonal-to-cubic transition in pollucite on heating.     

High-Temperature Phase Relations in the System Y2O3-Ta2O5

The phase relations for the system y₂o₃–Ta₂o₅ in the composition range 50 to 100 mol% Y₂O₃ have been studied by solid-state reactions at 1350°, 1500°, or 17000C and by thermal analyses up to the melting temperatures. Weberite-type orthorhombic phases (W2 phase, space group C222₁), fluorite-type cubic phases (F phase, space group Fm3m )and another orthorhombic phase (O phase, space group Cmmm )are found in the system. The W2 phase forms in 75 mol% Y₂O₃ under 17000C and O phase in 70 mol% Y₂O₃ up to 1700°C These phases seem to melt incongruently. The F phase forms in about 80 mol% Y₂O₃ and melts congruently at 2454° 3°C. Two eutectic points seem to exist at about 2220°C 90 mol% Y²O₃, and at about 1990°C, 62 mol% Y₂O₃. A Phase diagram including the above three phases were not identified with each other.     

Phase Equilibria in the Systems CaO–CuO and CaO-Bi2O3

New data are presented on the phase equilibria of the binary systems CaO-CuO and CaO-Bi₂O₃. Corrected compositions are reported for Ca.Bi₆O₁₃ and Ca₂Bi₂O₅ and a new metastable high-temperature phase is reported for a composition near Ca₆Bi₇O_16.5. The composition and decomposition temperatures for Ca_1–x.CuO₂ are given for both air and 1 atm of oxygen at 755 ± 5° and 835 ± 5°C, respectively.     

Glass-Free KxBa1−xGa2−xGe2+xO8 Ceramics for Low-Temperature Cofired Ceramics Technology: Synthesis, Phase Transitions, Sintering, and Microwave Dielectric Properties

K _x Ba_{1− x} Ga_{2− x} Ge_{2+ x} O₈ (0.6≤ x ≤1) polycrystalline ceramics are potential materials for glass-free low-temperature cofired ceramics (LTCC) substrates. We have made a comprehensive study of the kinetics of the monoclinic-to-monoclinic P 2₁/ a ⇔ C 2/ m phase transition. The low-temperature-stable P 2₁/ a phase with a high Q × f value was synthesized using a subsolidus method and was well sintered at the LTCC temperature with a H₃BO₃ additive. A good combination of low sintering temperature (910°–920°C), high Q × f values (96 700–104 500 GHz), low permittivities (5.6–6.0), and a small temperature coefficient of resonant frequency (∼−20 ppm/°C) was obtained for ceramics with x =0.67 and 0.9 and with 0.1 wt% of H₃BO₃.     

The Al2O3-Nd2O3 Phase Diagram

A tentative phase diagram for the system Al₂0₃-Nd₂O₃ is presented. Three compounds were obtained: a β -A1₂O₃-type compound, the perovskite NdAlO₃, and Nd₄Al₂O₉. The perovskite melts congruently (mp 2090°C), and the two other compounds exhibit incongruent melting behavior: β -Nd/Al₂O₃, mp 1900°C; Nd₄Al₂O₉, mp 1905°C. Two eutectics exist with the following compositions and melting points: 80 mol% Al₂O₃, 1750°C; 23 mol% Al₂O₃,1800°C. Nd₄Al₂O9 decomposes in the solid state at 1780°C.     

Phase Equilibria in the System Na2O – Nb2O5

Phase equilibria data, obtained both by differential thermal analysis and by quenching, are presented for the system Na₂O-Nb₂O₅. Five compounds corresponding to the formulas 3Na₂O.1Nb₂0₆, lNa₂O. 1Nb₂O₅, lNa₂O 4Nb₂O₆, lNa_zO.7Nb₂O₅, and lNa₂O. 10Nb₂O₆ have been found. The compound 3Na_z0.lNb₂O₅ melts congruently at 992°C. The compounds 1Na₂O. 4Nb₂O₆, lNa₂O.7Nb₂O, and 1Na₂O. 1Onb₂O₅ melt incongruently at 1265°, 1275°, and 1290°C., respectively. The well-known perovskite structure phase NaNbO₃ was found to melt congruently at 1412°C. The transition temperatures in NaNbO₅ were checked by thermal analysis and only the major structural changes at 368° and 640°C. could be detected. A new disordered form of NaNbO₃ could be preserved to room temperature by very rapid quenching.     

The System CaO–"CaCr2O4"–CaAl2O4 in Air and under Mildly Reducing Conditions

The system CaO–chromium oxide in air is reinvestigated and the existence of intermediate phases with chromium in oxidation states >3+ (Ca₅Cr₃O₁₂, Ca₃(CrO₄)₂, and Ca₅(CrO₄)₃) confirmed. Under reducing conditions these phases are unstable. A metastable, polymorphic form of calcium chromite, δ -CaCr₂O₄, is observed. In the CaO-rich section of the CaO–Al₂O₃–Cr₂O₃ system a ternary intermediate phase, chrome-haüyne, Ca₄[(Al,Cr³⁺)₆O₁₂](Cr⁶⁺O₄), coexists with calcium chromate and calcium aluminate phases. In air, low melting temperatures are preserved in all assemblages containing calcium chromate phases. Under reducing conditions a new ternary phase, Ca₆Al₄Cr₂O₁₅, coexists with CaO, CaCr₂O₄, chrome-haüyne, and calcium aluminate phases. The influence of chromium oxide additions on the solidus temperatures of the CaO–Al₂O₃ system is insignificant.     

Synthesis and Thermal Expansion Properties of the Ca(1+x)/2Sr(1+x)/2Zr4P6−2xSi2xO24 System

Ca_{(1+ x )/2}Sr_{(1+ x )/2}Zr₄P_{6−2 x} Si_{2 x} O₂₄( x ≤ 0.37) compositions, which belong to the [NZP] family of low-thermal-expansion materials, were synthesized using the solid-state reaction method. The lattice thermal expansion of members of this system was determined up to 1000°C by high-temperature X-ray diffractometry. The bulk thermal expansion and the microcracking during cooling also were investigated. These properties depended on the composition, on the synthesis method, and on the sintering conditions.     

Phase Relations in the System Al2O3–B2O3–Nd2O3

The phase relations at a temperature below "subsolidus" in the system Al₂O₃–B₂O₃–Nd₂O₃ are reported. Specimens were prepared from various compositions of Al₂O₃, B₂O₃, and Nd₂O₃ of purity 99.5%, 99.99%, and 99.9%, respectively, and fired at 1100°C. There are six binary compounds and one ternary compound in this system. The ternary compound, NdAl₃(BO₃)₄ (NAB), has a phase transition at 950°C ± 15°C. The high-temperature form of NAB has a second harmonic generation (SHG) efficiency of KH₂PO₄ (KDP) of the order of magnitude of the form which has been used as a good self-activated laser material, and the low-temperature form of NAB has no SHG efficiency.