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.     

Phase equilibria in the La2O3-Y2O3-Nd2O3 system at 1500 °C

The phase equilibria in the ternary La₂O₃-Y₂O₃-Nd₂O₃ system at 1500 °C were studied by X-ray diffraction, petrography, and electron microscopy in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcination at 1100 and 1500 °C. The solid solutions based on various polymorphous forms of source components and ordered phase of LaYO₃ were revealed in the system. The isothermal section of the phase diagram for the La₂O₃-Y₂O₃-Nd₂O₃ system has been developed. It was established that in the ternary La₂O₃-Y₂O₃-Nd₂O₃ system there exist fields of solid solutions based on hexagonal (A) and monoclinic (B) modifications of La₂O₃ and Nd₂O₃, cubic (C) modification of Y₂O₃, as well as perovskite-type structure of LaYO₃ (R) with rhombic distortions. The systematic study that covered the whole composition range excluded the 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 stability and equilibria in the La2O3–TiO2 system

XRD, electron probe wavelength and energy dispersive X-ray analyses were used to reexamine the phase relations in the La₂O₃–TiO₂ system. The diagram was redrawn to include the compound La₄Ti₃O₁₂ in addition to La₄Ti₉O₂₄, La₂Ti₂O₇ and La₂TiO₅. Above 1455°C a cation deficient perovskite La_2/3TiO₃ is stabilized by a small number of Ti³⁺ ions and remains stable on cooling in air. The proposed diagram represents a section through the system at the normal oxygen pressure in air at 1 atm, compositions being expressed in terms of the oxide components stable at room temperature.     

Phase equilibria in the ZrO2-YO1.5-TaO2.5 system at 1500 °C

The ZrO₂-YO_1.5-TaO_2.5 (ZYTO) system is of interest in phosphors, fuel cells, photocatalysis, and thermal barrier coatings. However, there is inadequate information on the ternary phase equilibria, especially in the ZrO₂-lean compositions. Precursor derived ZYTO compacts were heat treated at 1500 °C to elucidate the relevant phase relations. Chemical compositions measured using TEM/EDS and crystallographic information via x-ray diffraction, Raman spectroscopy and selected area electron diffraction were used to construct the isothermal section at 1500 °C, which was found to vary significantly from previous reports. It is shown for the first time that the fluorite field extends from the YO_1.5-ZrO₂ binary to the YO_1.5-TaO_2.5 binary, revealing a large YTaO₄ + fluorite phase field with potential engineering implications. The mutual solubility of ZrO₂ and YTaO₄ was quantified, and the presence of both YTa₃O₉ and YTa₇O₁₉ at 1500 °C was demonstrated. The emerging understanding helps identify compositions with potentially attractive properties for further investigation.     

Phase equilibria in TiO2-rich part of the MgO–CaO–TiO2 system at 1500–1600 °C

The equilibrium phase relations of the MgO–CaO–TiO₂ system were investigated at 1500–1600 °C in air using the high-temperature isothermal equilibration of samples in platinum crucibles followed by the rapid quenching technique. The phase compositions were analyzed using an electron probe X-ray microanalyzer (EPMA). The isothermal sections at 1500 °C and 1600 °C were constructed based on the experimentally determined liquid phase compositions. The present results deviate significantly from previous observations as well as the predictions by MTDATA and FactSage using their oxide databases, in particular in the perovskite primary phase field.     

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 La_1/3NbO₃ to the La₂O₃:3TiO₂ mixture completely stabilizes a perovskite-La_2/3TiO₃ compound, which is otherwise not stable at stoichiometric composition. On the other hand, a mixture La₂O₃:TiO₂ =1:3 dissolves in La_1/3NbO₃ 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 La₃Ti₅Nb₁₀O_39.5–La₂Ti₂Nb₈O₂₇ were proposed. In the binary subsystem LaTiNbO₆-La_0.462Ti_0.386Nb_0.614O₃, 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/La_0.462Ti_0.386Nb_0.614O₃ molar ratio of 0.27.     

Phase equilibria in the ZrO2-YO1.5-TaO2.5 system at 1250 °C

The phase relationships in the ZrO₂-YO_1.5-TaO_2.5 (ZYTO) system at 1250?°C—a temperature of interest for thermal barrier coatings applications—were investigated using precursor-derived powders. The system is bisected by a quasi-binary joining the tetragonal (t) ZrO₂ and monoclinic (M’) YTaO₄ solid solutions. The mutual solubility limits for these phases differ significantly depending on whether the third phase in equilibrium with t and M’ is fluorite or the orthorhombic (O) Zr₆Ta₂O₁₇. More importantly, the tetragonal phase in equilibrium with fluorite is non-transformable to the monoclinic form upon cooling, whereas that in equilibrium with O, which has lower stabilizer content, is transformable. The behavior contrasts with that previously observed for the equilibrium at 1500?°C, wherein the t phase on both sides of the quasi-binary is non-transformable. The fluorite solid solution extends from the ZrO₂-YO_1.5 binary to the YO_1.5-TaO_2.5 binary at 1250?°C, as previously shown for 1500?°C.     

Phase relations of the MgO–SiO2–CrOx system at 1600°C in air and reducing atmospheres

The equilibrium phase relations of the MgO–SiO₂–CrO_x system were investigated at 1600°C in air and at pO₂ of 10^–10 to 10^–11 atm using a high-temperature isothermal equilibration technique followed by rapid quenching and direct phase composition analyses with electron probe X-ray microanalysis. Two-phase equilibria (liquid–cristobalite, liquid–spinel, liquid–corundum, and liquid–olivine) and three-phase equilibria (liquid–cristobalite–spinel, liquid–olivine–spinel, liquid–spinel–corundum, and cristobalite–spinel–corundum) were observed. The 1600°C isothermal sections at various oxygen partial pressures were constructed for the MgO–SiO₂–CrO_x system based on the experimentally determined liquid and solid compositions. Data from the literature and the predictions by FactSage and MTDATA software were compared with the present experimental results.     

Flame-spraying synthesis of aluminate glasses in the Al2O3–La2O3 system

The paper deals with the synthesis and characterisation of binary aluminate glasses in the La₂O₃–Al₂O₃ system with Al₂O₃ contents changing between 74.6 and 86.9 mol% (48–65 wt.%), and of ternary glasses with 75.7 mol% Al₂O₃ doped with 1 mol% of Nd₂O₃ or Er₂O₃. Six binary and two ternary compositions were prepared. Flame synthesis facilitated the preparation of X-ray amorphous microspheres in the systems with 58 wt.% Al₂O₃, and with eutectic composition in the pseudobinary LaAlO₃–LaAl₁₁O₁₈ system doped with Er. Other systems contained low fractions of crystalline LaAlO₃ perovskite, regardless of the composition. The diameter of prepared microspheres ranged between 2 and 10 μm. They were transparent for visible light, as well as in the IR wavenumber range from 1300 to 4000 cm^?1.     

Stable garnets in the Er2O3–Sc2O3–Al2O3 oxide system for optical ceramics application

Erbium-scandium-aluminum garnets (ErSAG) with the maximum possible concentrations of scandium cations in the dodecahedral and octahedral positions of the crystal lattice have been synthesized. It has been established that in ErSAG at a temperature of 1600 °C the maximum possible concentration of scandium in the dodecahedral and octahedral position reaches 64.7 ± 2.0 at. % and 92.0 ± 2.0 at. %, respectively. The maximum possible concentrations of scandium cations in the dodecahedral position and the set of range of possible ErSAG compositions decrease at increasing of calcination temperature. It was shown that ceramics technique allow to produce the optical ceramics with compositions {Er_1.5Sc_1.5}[Sc_0.2Al_1.8](Al₃)O₁₂ (SAG: Er 50 at%) and {Y_1.57Er_0.03Sc_1.4}[Sc_0.2Al_1.8](Al₃)O₁₂ (YSAG: Er 1 at%), which can be considered as analogs of yttrium-aluminum garnet single crystals (YAG: Er 50 at% and YAG: Er 1 at%).     

Phase relations in ZrO2–La2 Zr2O7–Y2 Zr2O7system

Abstract

The phase relations in the system ZrO₂–La₂Zr₂O₇– Y₂Zr₂O₇ have been investigated using X-ray diffraction. Mixed oxide phase assemblages were prepared by hydrolysing zirconium butoxide with solutions of Y and La nitrates, followed by drying, calcining, and sintering. The cubic zirconia phase can accept into solid solution the larger, non-cubic stabilising lanthanum ion in the presence of a suitable proportion of the cubic stabilising oxide of yttrium. As the amount of the larger rare earth element ion is increased formation of pyrochlore and tetragonal type compounds is favoured.     

1250°C liquidus for the CaO–MgO–SiO2–Al2O3–TiO2 system in air

Ti-bearing blast furnace slags have been regarded as an important secondary material in modern society, and the efficient recycling of Ti oxides from it is of key interest. For this reason, more thermodynamic data is needed regarding the phase relations in different composition ranges and sections. Therefore, the equilibrium phase relations of CaO–MgO–SiO₂–Al₂O₃–TiO₂ system in a low w(CaO)/w(SiO₂) ratio of 0.6–0.8 at 1250 °C in air and fixed concentrations of MgO and Al₂O₃, were investigated experimentally using a high temperature equilibration and quenching method followed by SEM-EDS (Scanning Electron Microscope and Energy Dispersive X-ray Spectrometer) analyses. The equilibrium solid phases of perovskite (CaO·TiO₂), a pseudo-brookite solid solution (MgO·2TiO₂, Al₂O₃·TiO₂)_ss, and anorthite (CaO·Al₂O₃·2SiO₂) were found to coexist with the liquid phase at 1250 °C. The calculated results of Factsage and MTDATA were used for comparisons, and significant discrepancies were found between predictions and the experimental results. The 1250 °C isotherm has been constructed and projected on the CaO–SiO₂–TiO₂-8 wt.% MgO-14 wt% Al₂O₃ quasi-ternary plane of the phase diagram. The obtained results provide new fundamental data for Ti-bearing slag recycling processes, and they add new experimental features for thermodynamic modeling of the high-order titanium oxide-containing systems.     

Phase diagram of CaO–Al2O3-CeOx slag system at 1600 °C in reducing atmosphere and air atmosphere

CaO–Al₂O₃-CeO_x slag system is of great significance for designing a new type of metallurgical slag system suitable for rare earth steel. In this paper, the phase equilibria of CaO–Al₂O₃-CeO_x system were experimentally studied. Isothermal sections of CaO–Al₂O₃–Ce₂O₃ system and CaO–Al₂O₃–CeO₂ system at 1600 °C were constructed, respectively. 4 three-phase fields, 5 two-phase fields and a single liquid phase field in CaO–Al₂O₃–Ce₂O₃ system were determined; 2 three-phase fields, 3 two-phase fields and a single liquid phase field in CaO–Al₂O₃–CeO₂ system were determined. On this basis, the dissolution process of three typical inclusions (viz. Al₂O₃, CeAl₁₁O₁₈ and CeAlO₃) in CaO–Al₂O₃–Ce₂O₃ slag system was discussed.     

Phase equilibria studies in the CaO–SiO2–Al2O3–MgO system with CaO/SiO2 ratio of 0.9

Phase equilibria and liquidus temperatures in the CaO–SiO₂–Al₂O₃–MgO system at a CaO/SiO₂ weight ratio of 0.9 in the liquid phase have been experimentally determined employing high-temperature equilibration and quenching technique followed by electron probe X-ray microanalysis. Isotherms at 1573, 1623, 1673, and 1773 K were determined and the primary phase fields of wollastonite, melilite, olivine, periclase, spinel, and corundum have been located. Compositions of the olivine and melilite solid solutions were analyzed and discussed. Comparisons between the newly constructed diagram, existing data, and FactSage predicted phase diagrams were performed and differences were discussed. The present study will be useful for guidance of industrial practices and further development of thermodynamic modeling.     

Phase equilibria and stability of intermediate phases in the Sm2O3–BaO–Fe2O3 system

Phase equilibria in the ½ Sm₂O₃–BaO–½ Fe₂O₃ system were systematically studied at 1100°C in air. Two individual compounds: Sm_1.875Ba_3.125Fe₅O_15-δ and Ba₃SmFe₂O_7.5+δ have been detected in the studied system at 1100°C in air. One more complex oxide with double perovskite structure SmBaFe₂O_5+w has been obtained under reduced oxygen partial pressure. Thermodynamic stability of SmBaFe₂O_5+w and its thermal stability in metastable state in air were determined. The subsolidus phase diagram for the ½ Sm₂O₃ – BaO – ½ Fe₂O₃ system at 1100°C in air has been constructed.     

Thermodynamic calculation of Ms in ZrO2–CeO2–Y2O3 system

The difference of Gibbs free energy between tetragonal and monoclinic phases in ZrO₂–CeO₂–Y₂O₃ as a function of composition and temperature is thermodynamically calculated from the three related binary systems. In 8 mol% CeO₂–0.5 mol% Y₂O₃–ZrO₂, the equilibrium temperature between tetragonal and monoclinic phases, T₀, is obtained as 832.5 K and the M_s temperature of this alloy with a mean grain size of 0.90 μm is calculated as 249.9 K using the approach derived by Hsu et al. [J. Mater. Sci., 18(1983)3206; 20(1985)23; Acta Metall., 37(1989)3091; Acta Metall. Mater., 39(1991)1045; Mater. Trans. JIM, 37(1996)1284], which is in good agreement with the experimental one of 253 K.     

Phase equilibria in the system CaO–SiO2–Nb2O5–La2O3 at 1473 K with pO2=10−15.47 atm

Phase equilibria in the CaO–SiO₂–La₂O₃–Nb₂O₅ system are important for the utilization of Nb and Rare Earth resources. In the present work, phase equilibria in the CaO–SiO₂–La₂O₃–Nb₂O₅ system at 1473 K in H₂ (pO₂ = 10^−15.47atm) were studied by the equilibrium experiment. SEM, EDS and XRD analysis were employed to identify the equilibrium phase relations. The isothermal spatial phase diagram of the CaO–SiO₂–La₂O₃–Nb₂O₅ system and the isothermal section of CaO–SiO₂–Nb₂O₅-(5%, 10%) La₂O₃ pseudo-ternary system were constructed. A total of eight equilibrium phase regions were determined, including Liquid + CaNb₂O₆+CaSiO₃+LaNbO₄ region, Liquid + CaNb₂O₆+SiO₂+CaSiO₃ region, Liquid + CaSiO₃+CaNb₂O₆ region, Liquid + CaSiO₃+SiO₂ region, Liquid + CaNb₂O₆+SiO₂ region, Liquid + CaSiO₃ region, Liquid + SiO₂ region and Liquid + CaNb₂O₆ region. Additionally, the influence of pO₂ on equilibrium composition and temperature was also investigated considering its significant effect on phase equilibria in the slag system with variable valence elements. The results indicated that higher external pO₂ can increase the equilibrium O content in a slag system, while higher equilibrium temperature corresponds to higher equilibrium pO₂. Besides, the relationship between phase equilibria shown in the traditional slag system and in the related generalized alloy system was also revealed. The present experimental data can help further study on Nb-bearing and RE-bearing slag systems, and the theoretical conclusions will help the development of thermodynamic models.