Subsolidus Phase Equilibria Research Articles

Synthesis, crystal structures, and properties of new acentric glaserite-related compounds Rb7Ag5–3xSc2+x(XO4)9 (X = Mo, W)

The subsolidus phase equilibria in the system Ag2MoO4–Rb2MoO4–Sc2(MoO4)3 were studied and two new triple molybdates, Rb9Ag3Sc2(MoO4)9 and Rb7Ag5Sc2(MoO4)9, were found. The structures of Rb7Ag5Sc2(MoO4)9 and isostructural Rb7Ag5Sc2(WO4)9 of the Cs7Na5Yb2(MoO4)9 type (the space group R32) were determined. The found composition of the triple tungstate crystal, Rb7Ag4.61Sc2.13(WO4)9, indicates a non-stoichiometric compound formula, Rb7Ag5–3xSc2+x(WO4)9. Both structures have one incompletely occupied Ag site, and structure Rb7Ag4.61Sc2.13(WO4)9 also contains two positions with mixed Ag and Sc. Both compounds contain ‘lanterns’ [M2(XO4)9] (M = (Sc, Ag), Sc; X ​= ​Mo, W), which are strengthened by three AgO2 dumbbells to give isolated building blocks [Ag3M2(XO4)9] forming two-story hexagonal layers resembling the structure of glaserite K3Na(SO4)2. Similar layers of [Ag3Sc2(WO4)9]9− building blocks were also found by us in the structure of Rb9–xAg3+xSc2(WO4)9, which is close to that of Rb9Ag3Sc2(MoO4)9. Similar layers of the [M2(TO4)9] units were also observed in Cs7Na5Yb2(MoO4)9 and Na13Sr2Ta2(PO4)9. The title compounds belong to the series of rhombohedral triple molybdates and tungstates with a ≈ 9–10 ​Å and large c-periods (more than 20 ​Å), which have layered or open 3D framework structures. Like many compounds of this series, Rb7Ag5Sc2(XO4)9 (Х ​= ​W, Mo) at elevated temperatures have significant ionic conductivity reaching values 6.1·10−3 ​S ​cm−1 at 703 ​K (X ​= ​Mo) and 1.4·10−3 ​S ​cm−1 at 733 ​K (X ​= ​W) with Еа ​= ​0.7 ​eV and 0.6 ​eV, respectively.

Phase equilibria and microwave dielectric properties in the ternary La2O3–TiO2–Nb2O5 system

High-temperature phase relations in the La2O3–TiO2–Nb2O5 ternary system were investigated at 1290 °C using SEM, EDS and XRD, and a subsolidus phase equilibrium diagram was constructed. It was demonstrated that the addition of the La1/3NbO3 to the La2O3:3TiO2 mixture completely stabilizes a perovskite-La2/3TiO3 compound, which is otherwise not stable at stoichiometric composition. On the other hand, a mixture La2O3:TiO2 =1:3 dissolves in La1/3NbO3 up to 15 mol% TiO2. Moreover, a newly defined composition of compound La30Ti16Nb4O87 formed in the La2O3-rich part of the system and a solid solution La3Ti5Nb10O39.5–La2Ti2Nb8O27 were proposed. In the binary subsystem LaTiNbO6-La0.462Ti0.386Nb0.614O3, the components exhibit opposite temperature dependence of resonant frequency in the microwave frequency range. Thus, the dielectric properties of the prepared ceramics can be tailored by varying the component concentration and thermally stable dielectric properties can be achieved for a composition with a LaTiNbO6/La0.462Ti0.386Nb0.614O3 molar ratio of 0.27.

Integrated experimental phase equilibria study and thermodynamic modelling of the binary ZnO–Al2O3, ZnO–SiO2, Al2O3–SiO2 and ternary ZnO–Al2O3–SiO2 systems

Phase equilibria of the ZnO–SiO2, Al2O3–SiO2 and ZnO–Al2O3–SiO2 systems at liquidus were characterized at 1340–1740 °C in air. The ZnO–Al2O3 subsolidus phase equilibria were derived from the experiments with the SiO2- and CaO + SiO2-containing slags. High-temperature equilibration on silica or platinum substrates, followed by quenching and direct measurement of Zn, Al, Si and Ca concentrations in the phases with the electron probe X-ray microanalysis (EPMA) was used to accurately characterize the system. Special attention was given to zincite phase that was shown to consist of two separate ranges of compositions: round-shaped low-Al zincite (<2 mol.% AlO1.5) and platy high-Al zincite (4–11 mol.% AlO1.5). A technique was developed for more accurate measurement of the ZnO solubility in the low-ZnO phases (corundum, mullite, tridymite and cristobalite) surrounded by the ZnO-containing slag, using l-line for Zn instead of K-line, avoiding the interference of secondary X-ray fluorescence. Solubility of ZnO was found to be below 0.03 mol.% in corundum and cristobalite, and below 0.3 mol.% in mullite. Present experimental data were used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in this system using FactSage computer package. The modified quasichemical model with two sublattices (Zn2+, Al3+, Si4+) (O2−) was used for the liquid slag phase; the compound energy formalism was used for the spinel (Zn2+,Al3+)[Zn2+,Al3+,Va]2O2-4 and mullite Al3+2(Al3+,Si4+) (O2−,Va)5 phases; the Bragg-Williams formalism was used for the zincite (ZnO, Al2O3); other solid phases (tridymite and cristobalite SiO2, corundum Al2O3, and willemite Zn2SiO4) were described as stoichiometric. Present study is a part of the research program on the characterization of the multicomponent Pb–Zn–Cu–Fe–Ca–Si–O–S–Al–Mg–Cr–As–Sn–Sb–Bi–Ag–Au–Ni system.

Erbium-Doped Upconversion Phosphor in the Li2MoO4–BaMoO4–Y2(MoO4)3 System

We have investigated subsolidus phase equilibria in the Li2MoO4–BaMoO4–Y2(MoO4)3 system and constructed its phase compatibility diagram. A ternary molybdate with the composition Li3Ba2Y3(MoO4)8 and a monoclinic scheelite-like structure (sp. gr. C2/c) has been identified on the BaMoO4–LiY(MoO4)3 join. Doping Li3Ba2Y3(MoO4)8 with Er3+ ions, we obtained a Li3Ba2Y2.85Er0.15(MoO4)8 upconversion phosphor possessing efficient anti-Stokes luminescence in the range 530–850 nm under IR excitation (λex = 977 nm). The synthesized phosphor has been characterized by X-ray diffraction, differential thermal analysis, and IR spectroscopy.

Thermodynamic assessment of the CaO–Cu2O–FeO–Fe2O3 system

Thermodynamic assessment of the CaO–Cu2O–FeO–Fe2O3 system is presented. Effects of temperature and P(O2) on the phase equilibria involving slag, solubility of copper and the Fe3+/Fe2+ ratio in slag have been modeled using available experimental data. Subsolidus phase equilibria and concentration of iron in liquid copper were evaluated as well. Different ways of representing phase equilibria in a quaternary system are illustrated. The slag model, [Ca2+, Cu+, Fe2+, Fe3+][O2−], was developed using the Modified Quasichemical Model (MQM). Liquid metal phase is modeled using the MQM, but as a separate solution, (CuI, FeII, OII). Spinel phase is modeled using the Compound Energy Formalism (CEF) and takes into account the solubility of copper and calcium. A thermodynamic database produced in the present study can be used for predictions in pyrometallurgical processing of copper involving calcium ferrite slags. The database is internally consistent with the binary and ternary sub-systems published earlier, as well as with higher-order systems. It works in the environment of FactSage, ChemApp, ChemSheet and SimuSage software packages.

Phase Equilibria in the Li–W–Mn–O System

An isothermal compositional subsolidus phase equilibrium diagram of the Li–W–Mn–O system is constructed. Possible solid-state transformations in the system at a variable pressure and constant temperature are presented and phase transformations involving melt in temperature and pressure ranges of interest are analyzed.

Phase Stability of Lanthanum Nickelate (LNO) in LNO-Doped Ceria Composite Cathodes

Phase equilibria of La2NiO4+δ: LaxCe1-xO2-δ (LNO: LDC) composites (sintered at 1300°C) was studied using X-ray diffraction (XRD). The variables considered in these experiments were the dopant concentration in the ceria phase (0.2<x<0.48) and volume fractions of LNO in the composite cathode. This system has been previously evaluated and the sub-solidus phase equilibria between NiO, La2O3, and CeO2 at 1200°C was revisited, and studied at 1300°C and 800°C. A thermodynamic rationale was used to re-engineer the LNO: LDC composites which stabilized the LNO phase in the composite electrode. Elemental analysis via wavelength dispersive X-ray spectroscopy (WDS) confirmed the chemical composition of the stable phases in the composites. Measurements of the coefficient of thermal expansion (CTE) of LNO: LDC composites as a function of LNO volume fraction provided further evidence of the stability of LNO and LDC (for x=0.4). Finally, we have also performed electrical conductivities of La2NiO4+δ: La0.4Ce0.6O2-δ composites as a function of LNO volume fraction between 600 and 800°C in air. The electrical conductivity of the composites was analyzed via the resistive network approach. Based on these experiments, a window of composition is provided for stable, high performance cathode compositions in this system.

Subsolidus phase equilibria in the La2O3–Fe2O3–Sb2O5 system and characterization of layered ternary oxide LaFe0.5Sb1.5O6

Phase equilibria in the La2O3-Fe2O3–Sb2O5 system have been studied. The isothermal section was constructed at T=900°С. The existence of the ternary oxide LaFe0.5Sb1.5O6 was confirmed. The structure of this compound was solved using Rietveld refinement of synchrotron radiation-based powder XRD data. LaFe0.5Sb1.5O6 crystallizes in a trigonal layered structure relating to PbSb2O6 type (space group P-31m, a=b=5.2446(3)Å, c=5.1930(3)Å, Z=1). The fine powder of LaFe0.5Sb1.5O6 was prepared by molten salt synthesis. The compound was characterized by diffuse reflection and Mossbauer spectroscopy, magnetic measurements, scanning electron microscopy and photocatalytic tests. The magnetic behavior of LaFe0.5Sb1.5O6 in the applied magnetic field H=5000Oe is entirely paramagnetic. By contrast, in the small magnetic field H=100Oe the magnetic data of LaFe0.5Sb1.5O6 indicates an unusual critical behavior near phase transition at T<2K.

Synthesis, crystal structure, and thermal stability of new borates Na3REB2O6(RE = Pr, Sm, Eu)

Subsolidus phase equilibrium of Na2O–Sm2O3–B2O3system has been investigated mainly by solid-state reaction and powder X-ray diffraction method. There are nine definite three-phase regions and three ternary compounds determined under present experimental conditions. A novel compound Na3SmB2O6was found and confirmed in this system, along with its two homogeneous compounds Na3REB2O6(RE = Pr, Eu) synthesized for the first time. The indexing results showed that all three compounds crystallize in the monoclinic space groupP21/c(No.14) with the same structure type as both Na3NdB2O6and Na3GdB2O6. The lattice parameters (a, b, andc) of new borates Na3REB2O6(RE = Pr, Sm, Eu) decrease linearly with a decreasing radius of RE ion, which obeys the Lanthanide-contraction rule. The existence of a trigonal BO3group in the Na3REB2O6(RE = Pr, Sm) compounds was confirmed by analysis of their infrared absorption spectra. Thermal stabilities of the three new borates have been investigated.

Subsolidus phase equilibria and electrical properties of pyrochlores in the Bi2O3–CuO–Ta2O5 ternary system

Subsolidus phase relations had been determined for the Bi2O3–CuO–Ta2O5 (BCT) system over the temperature range 700–950 °C in air. Two structurally distinct ternary phases of different symmetries, a cubic pyrochlore and a monoclinic zirconolite were observed. Phase-pure pyrochlores existed in a unique boomerang-shaped area, which could be described using the general formula, Bi2.48+yCu1.92−xTa3.6+x−yO14.64+3x/2−y: 0.00(1) ≤ x ≤ 0.80(1) and 0.00 (1) ≤ y ≤ 0.60(1), respectively. BCT subsolidus pyrochlores exhibited low electrical conductivities, 10−7–10−6 S cm−1, moderate dielectric constants, ε′, ∼60–80 and low dielectric losses, tan δ, ∼0.01–0.20 at 1 MHz and ambient temperature, ∼28 °C. The recorded low activation energies, 0.32–0.40 eV suggesting these electroceramics were of semiconductor-type at elevated temperatures.

Subsolidus phase relations in CoO–In2O3–B2O3 system and crystal structure of Co3−XInXBO5 solid solution for 0 < X ⩽ 1

Subsolidus phase equilibrium of CoO–In2O3–B2O3 system has been investigated mainly by solid-state reaction and powder X-ray diffraction method. A novel compound Co2InBO5 was found and synthesized for the first time. There are five definite three-phase regions and one solid solution Co3−XInXBO5 (0<X⩽1) in this system under present experimental conditions. This new compound Co2InBO5 and high temperature metastable phase Co3BO5 can form continuous solid solution at all relative concentrations. Crystal structure of three representative Co3−XInXBO5 solid solution compounds (X=0.4, 0.7, and 1) were refined and determined from X-ray powder diffraction data using Rietveld method. The results showed that the Co3−XInXBO5 (0<X⩽1) solid solution crystallized in the orthorhombic space group Pbam (No. 55) with the ludwigite structure type. The lattice parameters (a, b and c) of these solid solution compounds increase linearly when In replace Co atom gradually (i.e. with the increase of the value of X), which obeys the Vegard’s rule. The trigonal BO3 group in these Co3−XInXBO5 solid solution compounds was confirmed by their infrared absorption spectra.

Phase Equilibria in the Mn-V-O System Near MnO-V2O3 Isopleth

Phase equilibria in the Mn–V–O system near MnO–V2O3 isopleth has been investigated in the temperature range from 1200°C to 1600°C and in the range of oxygen partial pressure from ∼10−6 to ∼10−13 atm. High-temperature equilibration, quenching and electron probe microanalysis were employed to obtain equilibrium compositions of liquid and several solid solutions. XRD analysis was also employed to confirm the stable phases. The phases which have been observed are; liquid oxide, (MnO)s.s., (V2O3)s.s., and (MnV2O4)s.s.. The (MnV2O4)s.s. phase was confirmed to be the only intermediate phase near the MnO–V2O3 isopleth under the conditions in the present study. It was found that sub-solidus phase equilibria are considerably affected by the oxygen partial pressure. From the effect of oxygen partial pressure on the sub–solidus phase equilibria, the structures (Mn2+, V2+)T(Mn2+, Mn3+, Mn4+, V3+, Va)O4, (V3+, Mn3+, V4+)2O3+y and (Mn2+, Mn3+, V2+)1−zO are proposed for MnV2O4, V2O3, and MnO solid solutions, respectively.

Crystal structure and photoluminescence of Tb 3+-activated Ba 3InB 3O 9

Subsolidus phase equilibrium of BaO–In 2O 3–B 2O 3 system has been investigated mainly by solid-state reaction technique and powder X-ray diffraction method. There are 15 definite three-phase regions under present experimental conditions. Two ternary compounds, Ba 3InB 9O 18 and Ba 3InB 3O 9 were found and confirmed in this system. Crystal structure of Ba 3InB 3O 9 was determined from X-ray powder diffraction data using Rietveld method. It crystallizes in space group R 3 ¯ with six formula units of a cell with a = 12.7713(4) Å, c = 9.3950(2) Å and V = 1327.09(8) Å 3. Coordination surrounding of B–O in this structure, [BO 3] 3− group, was confirmed by infrared absorption spectrum of Ba 3InB 3O 9. Ba 3In 1− x Tb x B 3O 9 ( x = 0.1–0.5) phosphors exhibited green emission at about 543 nm with 370 nm light excited. There is neither emission from 5D 3 level nor concentration quenching observed in the case of Ba 3InB 3O 9:Tb 3+, which can be explained from the crystal structural features of the matrix Ba 3InB 3O 9. Chemical stabilization, simple preparation, and luminescence characteristics make phosphors Ba 3InB 3O 9:Tb 3+ have potential applications in white light-emitting diodes.

Subsolidus phase equilibria in the CaO-poor part of the RuO2–CaO–V2O5 system

Subsolidus phase equilibria in the CaO-poor part of the RuO2–CaO–V2O5 system

Subsolidus phase equilibria in the CaO-poor part of the RuO2–CaO–SiO2 system

During firing the conductive phase based on CaRuO3 in lead-free thick-film resistors decomposes, presumably due to interactions with the silica-rich glass phase. Subsolidus equilibria in the CaO-poor part of the RuO2–CaO–SiO2 diagram were studied with the aim of investigating possible interactions between the conductive phase and silica-rich glasses in thick-film resistors. The tie lines are between CaRuO3 and CaSiO3, and between RuO2 and CaSiO3. This indicates that the calcium ruthenate is not stable in the presence of the silica-rich glass phase.

Phase Equilibria of BaO-R2O3-CuO z Systems (R = Y and Lanthanides) under CO2-free Conditions

For applications ranging from phase equilibria to the processing of second-generation high Tc superconductor-coated-conductors, phase diagrams constructed under carbonate-free conditions are needed. Subsolidus phase equilibria of BaO-R2O3-CuOz (R = Ho) have been investigated at \( {\hbox{p}}_{{{\rm{O}}_{{\rm{2}}} }} \hbox{\,=\,} 100\;{\hbox{Pa}} \) (810°C), 21 kPa (875°C) and 0.1 MPa (850 and 930°C) by applying controlled atmosphere methods to minimize the presence of carbonate and CO2 and H2O contamination. Under carbonate-free conditions, most of these phase diagrams are different from those reported in the literature. In this paper, we also review and compare the phase diagrams of ten BaO-R2O3-CuOz systems (R = Nd, Sm, Eu, Gd, Dy, Y, Ho, Er, Tm and Yb) that were previously determined in this laboratory under \( {\hbox{p}}_{{{\rm{O}}_{{\rm{2}}} }} \hbox{\,=\,} 100\;{\hbox{Pa}}{\hbox{.}} \) Among these diagrams, a distinct trend of phase formation and tie-line relationships is observed.

Subsolidus phase equilibria in the PbO-poor part of the TiO2–PbO–SiO2 system and its application in low-temperature thick-film dielectrics

Subsolidus equilibria in the PbO-poor part of the TiO2–PbO–SiO2 diagram were studied with the aim of investigating possible applications for low-temperature thick-film dielectrics. The tie lines are between PbTiO2 and PbSiO3, and between PbTiO3 and SiO2. The results show that the TiO2, when added to low-temperature softening point glasses, reacts with the PbO from the glass, so forming PbTiO3. These results were applied to a low-temperature firing dielectric, consisting of a lead-rich PbO–SiO2–B2O3 glass filled with a TiO2 powder. The conversion of TiO2 to the PbTiO3 crystalline phase was observed above firing temperatures of approximately 600 °C. The kinetics of the reaction depend on the particle size of the TiO2.

Subsolidus phase equilibria in the PbO-poor part of RuO 2–PbO–SiO 2 system

After long-term high-temperature firing, the conductive phase in thick film resistors based on RuO 2 remains unchanged. In contrast, ruthenates decompose, presumably due to interactions with the silica-rich glass phase. Subsolidus equilibria in the PbO-poor part of the RuO 2–PbO–SiO 2 diagram were studied with the aim of investigating possible interactions between the conductive phase (either ruthenium oxide or lead ruthenate) and silica-rich glasses in thick-film resistors. The tie lines are between Pb 2Ru 2O 6.5 and PbSiO 3, and between RuO 2 and PbSiO 3. This indicates that the lead ruthenate is not stable in the presence of the silica-rich glass phase.

Experimental Study of Phase Equilibria in the MnO-"TiO2"-"Ti2O3" System

Phase equilibria and liquidus in the system MnO-“TiO2”-“Ti2O3” under controlled atmosphere have been investigated in the temperature range from 1300 to 1550°C and in the range of log pO2 (in atm) from -7.2 (pCO/pCO2=1) to -16.6 (C-CO equilibration). High-temperature equilibration, quenching and electron probe microanalysis (EPMA) were employed to obtain equilibrium compositions of liquid and several solid solutions. The following phases have been observed; molten oxide, manganosite (MnO (s.s.)), rutile (TiO2-δ (s.s.)), spinel (Mn2TiO4-MnTi2O4), pyrophanite (MnTiO3-Ti2O3) and pseudobrookite (“MnTi2O5”-Ti3O5) solid solutions. Liquidus of manganosite and rutile were measured and compared with previous investigations. “MnTi2O5” compound was confirmed to be unstable phase in the MnO-“TiO2” system. It was found in the present study that sub-solidus phase equilibria are affected considerably by oxygen partial pressure.

Phase equilibria and primary crystallisation field for Sm 1+ yBa 2− yCu 3O 7 at various p(O 2)

Phase relations in the Sm–Ba–Cu–O system in air have been reconsidered and the topology at the liquidus surface has been consistently constructed from both new experimental investigation as well as critical review of literature data. Subsolidus phase equilibria near the superconducting Sm 1+ x Ba 2− x Cu 3O 7 (“Sm123”) phase have also been investigated at various oxygen partial pressures, revealing the strong influence of the oxygen chemical potential on the extension of the homogeneity region of the Sm123 phase. The decomposition temperature of Sm123 decreases rapidly from 1070 °C down to 1010 °C with the Sm excess x increasing from ∼0 to ∼0.5. For x > 0.5 the decomposition temperature is constant indicating an invariant reaction which marks the lowest temperature at which the Cu-rich melt is in equilibrium with both Sm123 and Sm 2BaCuO 5 (“Sm211”). For Cu-poor melts this temperature is 1030 °C in air (0.21 bar O 2). Implications of the results with respect to both sample growth during melt texturing and post annealing (decomposition of Sm-rich Sm123) in different atmospheres are being discussed. A p(O 2)- T-diagram for equilibria containing Sm-rich Sm123 is derived.