Phase diagram study and thermodynamic assessment of the Y2O3-YF3 system

The phase diagram of the Y₂O₃-YF₃ system up to 1973 K was investigated using a classical equilibration/quenching experiment and differential thermal analysis (DTA). Equilibrium phases were confirmed by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) phase analysis. For the very first time, the entire range of the phase diagram of yttrium oxy-fluoride system up to 1973 K was experimentally determined. Cubic-Y₂O₃ phase dissolves more than 5 mol% of YF₃ at 1973 K. The melting points of YOF and vernier phases are found to be higher than 1973 K and their steep liquidus in the YF₃-rich region are determined. Based on new experimental phase diagram data and thermodynamic property data in the literature, the Y₂O₃-YF₃ system was thermodynamically modeled by the CALculation of PHAse Diagram (CALPHAD) method. As applications of the thermodynamic database, metastable solubilities of YF₃ in Y₂O₃ during plasma etching process were calculated.     

Phase diagram study and thermodynamic assessment of the Na2O-ZrO2 system

The phase diagram of the Na₂O-ZrO₂ system was experimentally investigated using the classical equilibration/quenching method and differential thermal analysis (DTA) followed by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) phase analysis. For the first time, the general feature of the phase diagram between Na₂ZrO₃ and ZrO₂ above 1773 K was revealed experimentally. The eutectic reaction between NaZrO₃ and cubic-ZrO₂ was found at 64.8 mol % ZrO₂ at 1883 ± 3 K. Cubic-ZrO₂ was stabilized by the dissolution of Na₂O (maximum solubility of 7.1 mol % Na₂O at 1883 ± 3 K). Based on new experimental phase diagram data in this study and thermodynamic property data of Na₂ZrO₃ in the literature, the Na₂O-ZrO₂ system was thermodynamically optimized using the CALculation of PHAse Diagram (CALPHAD) method and a consistent set of the Gibbs energy functions for all phases in the binary system was prepared.     

A coupled phase diagram experimental study and thermodynamic optimization of the Li2O-CaO-Al2O3 and Li2O-CaO-SiO2 systems,and prediction of the phase diagrams of the Li2O-CaO-Al2O3-SiO2 system

A coupled experimental phase diagram study and thermodynamic modeling of the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems was conducted at 1 atm total pressure. Differential scanning calorimetry (DSC) measurements were performed in the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems. In addition, the phase relations in the Li₂O-CaO-Al₂O₃ system were determined by equilibration/quenching experiments at 1643 and 1743 K, and the phases were characterized with X-ray diffraction (XRD) and Electron-probe micro analysis-wavelength dispersive spectroscopy (EPMA-WDS). The absence of ternary compounds or solid solutions was confirmed. Congruent melting of Li₂CaSiO₄ compound in the Li₂O-CaO-SiO₂ system was determined at 1350 ± 5 K. Thermodynamic optimization of the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems was carried out based on new phase diagram experiments and critically evaluated literature data. The phase diagrams of the quaternary Li₂O-CaO-Al₂O₃-SiO₂ system were predicted using the thermodynamic models with optimized model parameters.     

Phase diagram of the Al2O3–ZrO2–La2O3 system

The phase diagram of the Al₂O₃–ZrO₂–La₂O₃ system was constructed in the temperature range 1250–2800 °C. The liquidus surface of the phase diagram reflects the preferentially eutectic interaction in the system. Three new ternary and two new binary eutectics were found. The minimum melting temperature is 1665 °C and it corresponds to the ternary eutectic LaAlO₃ + T-ZrO₂ +  La₂O₃·11Al₂O₃. The solidus surface projection and the schematic of the alloy crystallization path confirm the preferentially congruent character of phase interaction in the ternary system. The polythermal sections present the complete phase diagram of the Al₂O₃–ZrO₂–La₂O₃ system. No ternary compounds or regions of remarkable solid solution were found in the components or binaries in this ternary system. The latter fact is the theoretical basis for creating new composite ceramics with favorable properties in the Al₂O₃–ZrO₂–La₂O₃ system.     

Heterostructural phase diagram of Ga2O3–based solid solution with Al2O3

Ga₂O₃, which is emerging as semiconductor material due to the ultra-wide bandgap, has tunability in bandgap and lattice constant by alloying Al. However, successful control of alloying phase is still challenging due to its heterostructural nature and rich polymorphs. Here, we identified the thermodynamic phase diagram of heterostructural (Al_xGa_1-x)₂O₃ alloy. Using density-functional theory (DFT) calculations and regular solution model, we calculated the Gibbs-free energy of mixing of heterostructural polymorphs. Based on the calculation, we show the phase diagram of (Al_xGa_1-x)₂O₃ alloy system with a markedly increased metastability than the isostructural alloy, which can make a vast phase space for homogeneous single-phase alloys. We also investigated the correlation between the bandgap and lattice constant within these systems using hybrid DFT calculations, which can guide the device design of Ga₂O₃ power electronics.     

Phase relation studies in the CeO2–La2O3–Er2O3 system at 1500°C

Materials based on CeO₂–La₂O₃–Er₂O₃ system are promising candidates for a wide of applications, but the phase relationship has not been studied systematically previously. To address this challenge, the isothermal section of the phase diagram for 1500 °C was investigated. The phase relations in the CeO₂–La₂O₃–Er₂O₃ ternary system at 1500 °C were studied by X-ray diffraction and scanning electron microscopy in the overall concentration range. To study phase relationships at 1500 °C the as-repared samples were thermally treated in two stages: at 1100 °C (for 300 in air) and then at 1500 °C (for 70 h in air) in the furnaces with heating elements based on Fecral (H23U5T) and Superkanthal (MoSi2), respectively. The solid solutions based on various polymorphous forms of constituent phases and with perovskite-type structure of LaErO₃ (R) with orthorhombic distortions were revealed in the system. No new phases were found. The isothermal section of the phase diagram for the CeO₂–La₂O₃–Er₂O₃ system has been constructed. It was established that in the ternary CeO₂–La₂O₃–Er₂O₃ system there exist fields of solid solutions based on hexagonal (A) modification of La₂O₃, cubic modification of CeO₂ with fluorite-type structure (F), cubic modification Er₂O₃ and with perovskite-type structure of LaErO₃ (R) with orthorhombic distortions. The maximal solubility of ceria in LaErO₃ was found to be around ∼ 2 mol% CeO₂ along the section CeO₂–(50 mol % La₂O₃ –50 mol% Er₂O₃).     

Isothermal section of CaO-SiO2-La2O3 system within specific region at 1673–1473 K

So far, the relevant phase equilibrium relations and the type of equilibrium phase fields in the CaO-SiO₂-La₂O₃ basic slag system phase diagram are still unknown, which restricts the smelting process and application in materials of rare earth elements. In the current work, phase equilibrium relations within specific region of CaO-SiO₂-La₂O₃ system at 1673–1473?K were studied experimentally by using the thermodynamic equilibrium experiment followed by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). According to the experimental results, the existence of ternary compound CaO·3SiO₂·2La₂O₃ was determined, it is confirmed to be a solution solid phase. The sub-solidus phase relations between different solid phases were also determined. Finally, the isothermal sections of CaO-SiO₂-La₂O₃ system within specific region at 1673?K, 1573?K and 1473?K were obtained, respectively. The experimental results can not only enrich the phase diagram information of silicate system, but also have practical significance for the application of rare earth in materials.     

Thermodynamic modeling of the K2O-Al2O3 and K2O-MgO-Al2O3 systems with emphasis on β- and βʹʹ-aluminas

A critical evaluation and thermodynamic modeling study including key phase diagram experiments was performed to investigate the K₂O-Al₂O₃ and K₂O-MgO-Al₂O₃ systems. For the first time, potassium β- and β??-alumina solid solutions were described using the Compound Energy Formalism with accurate cation distributions in their sublattices. From the new experimental results, the stability of potassium β??-alumina was assured up to 1600?°C. A large discrepancy reported in the literature, the eutectic temperature between KAlO₂ and β-alumina in the K₂O-Al₂O₃ system, was resolved. A set of self-consistent Gibbs energy functions for all stable phases in the K₂O-MgO-Al₂O₃ system was obtained. As a result, any phase diagram sections and thermodynamic properties of the K₂O-MgO-Al₂O₃ system can be calculated from the optimized Gibbs energy functions. In particular, the cation distribution in the β- and β??-alumina solid solutions is calculated depending on the non-stoichiometry of solution and temperature.     

Thermodynamic optimization of the K2O-Al2O3-SiO2 system

A critical evaluation and thermodynamic optimization of experimental phase diagrams and thermodynamic properties of the K₂O-Al₂O₃-SiO₂ system was performed at 1?bar total pressure. A set of self-consistent thermodynamic functions of all phases in the K₂O-Al₂O₃-SiO₂ system was obtained. The liquid phase was described using the Modified Quasichemical Model with the KAlO₂ associate component. The set of optimized model parameters obtained for all phases reproduces available and reliable thermodynamic properties and phase diagram data as well as the melt structure of the K₂O-Al₂O₃-SiO₂ system within the experimental error limits.     

Phase diagram of the Al2O3-HfO2-Y2O3 system

The phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al₂O₃ + HfO₂ + Y₃Al₅O₁₂. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system.     

Thermodynamic modeling of the CaO-SiO2-ZrO2 system coupled with key phase diagram experiments

Thermodynamic modeling coupled with key phase diagram experiments of the ternary CaO-SiO₂-ZrO₂ system was carried out. The isothermal phase diagram of the CaO-SiO₂-ZrO₂ system at 1873 K was established by using a classical phase equilibration and quenching technique followed by EPMA phase analysis. The Gibbs energy of each phase was optimized through critical evaluation of all available thermodynamic properties and phase diagram data in literature with new experimental data. The discrepancies between experimental phase diagram data and possible errors in the existing thermodynamic data were resolved in this study.     

Phase Relationships in the NaPO3–Al2O3 Glass-Forming System

The phase formation is studied in the NaPO₃–Al₂O₃ system (0–25 mol % Al₂O₃). It is shown that two individual compounds, namely, Na₆Al₂(P₂O₇)₃ and Na₃Al₂(PO₄)₃, exist along the studied join. The phase diagram of the NaPO₃–Al₂O₃ system (0–25 mol % Al₂O₃) is constructed. The phase separation phenomena are revealed in the melt.     

Phase relation studies in the CeO2-Eu2O3 system at 1500 to 600 °C in air

Materials based on CeO₂-Eu₂O₃ system are promising candidates for a wide range of applications, but the phase relationship has not been studied systematically previously. To address this challenge, the subsection of the phase diagram for 600, 1100 and 1500 °C has been elucidated. Samples of different compositions have been prepared from nitrate acid solutions using conventional ceramic techniques; evaporation, drying, and calcinations. The phase relations in the binary CeO₂-Eu₂O₃ system at 600–1500 °C in air were studied from the heat treated samples using X-ray diffraction analysis, polarized light microscopy investigation and scanning electron microscopy in the overall concentration range. It was established that in the binary CeO₂-Eu₂O₃ system there exist fields of solid solutions based on monoclinic (B) modification of Eu₂O₃, cubic (C) modification of Eu₂O₃ and cubic modification of CeO₂ with fluorite-type structure (F). The systematic study that covered whole composition range excluded formation of new phases. The refined lattice parameters of the unit cells and the boundaries of the homogeneity fields for solid solutions were determined.     

Liquid phase formation in the system Al2O3–Y2O3–AlN: Part II. Thermodynamic assessment

The mixing parameters of liquid phase in the Al₂O₃–Y₂O₃–AlN system were assessed based on differential thermal analysis (DTA) and scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDX) investigations of selected compositions. Phase diagram of the Y₂O₃–AlN system was calculated. Liquidus surface of the Al₂O₃–Y₂O₃–AlN system was constructed and compared with experimental results on primary crystallisation fields. Calculated temperatures of invariant reactions were in agreement with DTA results. Vertical sections of the Al₂O₃–Y₂O₃–AlN system were calculated and compared with experimental data     

Monotectic crystallization of melts in the ZrO2-Al2O3 system

The morphology of the crystalline phases prepared at different cooling rates, temperatures, and compositions of melts in the ZrO₂-Al₂O₃ system is investigated. It is established that both the quenched and slowly crystallized samples containing 35–70 wt % ZrO₂ have a submicron structure. Outside this concentration range, the ingots have a zonal structure: the peripheral region is formed by large baddeleyite crystals (at a ZrO₂ content higher than 70 wt %) or corundum crystals (at a ZrO₂ content lower than 30 wt %). This character of the crystallization confirms the presence of the phase separation (liquid immiscibility) region in melts of this system. A variant is proposed for the phase diagram of the system under investigation.     

Experimental study of the phase relationships in the SrO-SiO2 system

The phase relationships in the SiO₂-SrO system were determined experimentally using the quenching technique in the temperature range between 1573?K (1300?°C) and 1898?K (1625?°C). The phases in the quenched samples were examined and identified using light optical microscopy (LOM), scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS). The presence of solid phases and their nature were further confirmed using X-ray Diffraction (XRD). Based on the experimental results, the phase diagram was constructed. The phase diagram shows a congruent melting of the SrSiO₃ at 1840?K (1567?°C). The eutectic between the SrSiO₃, SiO₂ and liquid happens at 1608?K (1335?°C) and 67?mol% SiO₂ and the eutectic between the SrSiO₃, Sr₂SiO₄ and liquid at 1835?K (1562?°C) and 46.5?mol% SiO₂.     

Phase relation studies in the CeO2-La2O3 system at 1100-1500 °C

Materials based on CeO₂-La₂O₃ system are promising candidates for a wide range of applications, but the phase relationship has not been studied systematically previously. To address this challenge, the subsection of the phase diagram for 1100 and 1500 °C have been elucidated. Samples of different compositions have been prepared from nitrate acid solutions using conventional ceramic techniques; evaporation, drying, and calcinations. The phase relations in the binary CeO₂-La₂O₃ system at 1100-1500 °C were studied from the heat treated samples using X-ray diffraction analysis, petrographic investigation and scanning electron microscopy in the overall concentration range. It was established that in the binary CeO₂-La₂O₃ system there exist fields of solid solutions based on hexagonal (A) modification of La₂O₃, and cubic modification of CeO₂ with fluorite-type structure (F). The systematic study that covered whole composition range excluded formation of new phases. The refined lattice parameter of the unit cell and the boundaries of the homogeneity fields for solid solutions were determined.     

Phase equilibria in the Bi2O3-CuO-Nb2O5 ternary system

A complete subsolidus ternary phase diagram of the Bi₂O₃-CuO-Nb₂O₅ (BCN) system was constructed. Careful firing control and phase analysis were applied to determine the phase assemblages and compatibilities over a wide range of temperatures, i.e. 700–925 °C. Phase-pure BCN pyrochlores were found to crystallise in cubic symmetry, space group Fd3m, No. 227 with lattice constants in the range of 10.4855 (5)<x<10.5321 (3). The mechanism of this limited subsolidus series could be represented by a general formula, Bi_3.08−xCu_1.84+2x/9Nb_3.08+7x/9O_14.16+6x/9 (0≤x≤0.36) wherein the reduction in Bi content was compensated by a proportion amount of copper and niobium together with non-stoichiometry in oxygen.