Investigation of the formation of solid substitution solutions based on gadolinium and yttrium aluminates with perovskite structure

Currently, compounds with the perovskite structure are of great interest, this is due to the peculiarities of their structure. Perovskites have the general formula ABX3 and have a framework structure. The framework consists of octahedrons BX6 interconnected by vertices, and dodecahedral cavities formed by these octahedrons are filled with A ions. Due to this structure, isomorphic substitutions at the A position can easily occur. This makes it possible to develop materials with new properties. This work is devoted to the study of the formation of the crystal structure of solid solutions based on yttrium and gadolinium aluminates with the structure of perovskite composition GdxY(1-x)AlO3, where x = 1; 0.875; 0.75; 0.625; 0.5; 0.25; 0. Gadolinium and yttrium orthoaluminate and solid solutions based on them were obtained by the nitrate-citrate sol-gel method. The optimal annealing temperature necessary for obtaining individual gadolinium orthoaluminate was determined by methods of thermal and X-ray phase analysis. Phase formation was investigated by X-ray phase analysis, and found that when obtaining gadolinium orthoaluminate is formed single-phase gadolinium aluminate GdAlO3 with the structure of perovskite (space group Pbnm), solid solutions in these conditions are formed at a ratio of Gd3+:Y3+ = 87,5:12,5 and Gd3+:Y3+ = 75:25, with a further increase in the concentration of yttrium is the formation of multiphase systems. According to the shift of diffraction maxima, indicating a change in the unit cell parameters, and the results of micro X-ray diffraction analysis, the formation of solid solutions was confirmed. By results of XRD after refinement by Rietveld method, crystallographic data were obtained, on the basis of which the structures of solid solutions were constructed in Vesta program. The parameters of polyhedra were calculated, which showed that the introduction of yttrium ion in the structure of gadolinium orthoaluminate leads to an increase in the volume of the polyhedron. The influence of the introduction of yttrium on the framework system was also shown. By the Williamson-Hall method, using the Lorentz approximation, we calculated the coherent scattering regions (CSR) and microstrain values for the obtained solid solutions, and saw that the CSR and micro-deformations values for all solid solutions have close values.