Abstract
Materials based on cerium oxide, stabilized by oxides of rare earth elements, are promising for use in medicine, energy and mechanical engineering due to the uniqueness of their properties. State diagrams of CeO2–La2O3–Ln2O3 systems are the physicochemical basis for the creation of solid electrolytes for fuel cells, oxygen gas sensors, catalyst carriers, protective coatings on alloys, etc. Phase equilibria and structural transformations in CeO2–La2O3–Gd2O3 systems at temperatures 1250 and 1500 °С and in the binary system La2O3–Gd2O3 at temperatures 1100, 1500 and 1600 ° С in the whole range of concentrations were investigated using X-ray phase and microstructural analyzes. It was found that solid solutions based on cubic (F) modification with CeO2 fluorite type, monoclinic (B) and cubic (C) modifications of Gd2O3 and hexagonal (A) modification of La2O3 are formed in the ternary system CeO2–La2O3–Gd2O3. The boundaries of the phase fields and the periods of the crystal lattices of the formed phases are determined. It is established that in the CeO2–La2O3 –Gd2O3 system at 1250 and 1500 °С the phases of cubic symmetry are in equilibrium: on the basis of F–CeО2 with the spatial group Fm3m and C-phase on the basis of Gd2O3 with the spatial group Ia3. As the temperature decreases, there is a narrowing of all areas of homogeneity.
Highlights
Materials based on cerium oxides and lanthanides are widely used in high-tech industries
Studies of the solid-phase interaction of La2O3 and Gd2O3 at 1600, 1500 °C showed that two types of solid solutions are formed in the La2O3–Gd2O3 system: based on hexagonal А-La2O3 modification and monoclinic modification of B-Gd2O3, which are separated by a two-phase field (A + B)
At 1250 °C, cubic solid solutions with a structure of the type of fluorite based on cerium dioxide are in equilibrium with all the phases formed in this system
Summary
Materials based on cerium oxides and lanthanides are widely used in high-tech industries. There are no data on the thermodynamic stability of solid solutions based on oxides of cerium, lanthanum and gadolinium in the literature, which necessitates the study of phase equilibria in the ternary system CeO2–La2O3–Gd2O3. It is established that two types of solid solutions are formed in the CeO2–La2O3 system: cubic phase F based on CeO2 fluorite and hexagonal phase A based on the compound La2O3, the homogeneity regions of which are separated by a two-phase field (A + F). In the CeO2–Gd2O3 system in the temperature range 1500–600 °С, solid solutions with cubic phase F of fluorite type (CeO2) and cubic C based on structural type Tl2O3 (Gd2O3) are formed, as well as solid solutions based on monoclinic modification of rare. It is established that in the La2O3–Gd2O3 system three types of continuous solid solutions are formed on the basis of hexagonal (A and H) and cubic (X) modifications of REE oxides. The International Powder Standards Committee database (JSPSDS International Center for Diffraction Data 1999) was used to identify the obtained X-ray diffraction results
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