We synthesized samarium oxotellurites SmMTeO4.5 (M — Mg, Ba) by the method of ceramic technology with solid-phase interaction (800–1200 °С) of Sm2O3 and TeO2 oxides with MgCO3 and BaCO3 carbonates. The compounds were characterized by X-ray and electrophysics methods. It has been established that the syn-thesized compounds crystallize in the tetragonal syngony with the following crystallographic characteristics: SmMgTeO4.5 — a = 12.226; c = 5.783 Å, V0un.cell = 864.38 Å3, Z = 4, ρxray. = 2.876, ρpycn. = (2.874±0.002) g∙cm-3; SmBaTeO4.5 — a = 12.717; с = 6.132Å, V0un.cell = 991.62Å3, Z = 4, ρxray. = 3.264, ρpycn. = (3.260±0.004) g∙cm-3; for both tellurites α = β = γ = 90°. The experimental and calculated values of 2 Th and d-sp, X-ray and pycnometric densities, as well as theoretical and experimental values of unit cell volumes are agreed satisfac-torily. Thus, we can confirm correctness and reliability of the results of indexing X-ray patterns of new sa-marium oxotellurites. We found that increase in the ionic radii from Mg to Ba increases the lattice parameters of the synthesized oxotellurites. Oxotellurites are crystallized in the structural types of distorted perovskite Pm3m. Based on the given study samarium oxotellurites can have semiconductor and ferroelectric properties.

For the first time, double gadolinium tellurites of the composition GdMIITeO4.5 (MII — Sr, Ba) were synthesized by the solid-phase method. The solid-phase synthesis of samples was carried out from decrepitated gadolinium (III) and tellurium (IV) oxides, strontium, and barium carbonates according to the standard ceramic technology. The synthesis was carried out in the temperature range of 800-1100 °C. The samples obtained were confirmed by X-ray phase analysis. X-ray phase analysis was carried out on an Empyrean instrument in the XRDML Pananalitical format. The intensity of the diffraction maxima was estimated on a 100-point scale. X-ray diffraction patterns indexing of the powder of gadolinium tellurites — alkaline earth metals studied were carried out by the homology method. The reliability and correctness of the results of indexing the X-ray diffraction patterns are confirmed by the good agreement between the experimental and calculated values of the interplanar distances (d) and the agreement between the values of the X-ray and pycnometric densities. It was found that compounds GdSrTeO4.5 and GdBaTeO4.5 crystallize in the monoclinic system and have the unit cell parameters, namely GdSrTeO4.5 — a = 12.7610, b = 10.4289, c = 8.6235 Å, V° = 1141.83 Å3, β = 95.77°, Z = 5, ρrent. = 3.22, ρpikn. = (3.10±0.09) g/cm3; GdBaTeO4.5 — a = 15.7272, b = 15.8351, c = 7.1393 Å, V° = 1769.72 Å3, β = 95.53°, Z = 8, ρrent = 3.71, ρpick = (3.61±0.10) g/cm3. Using the Landiya method, the standard heat capacities of the compounds were estimated from the calculated values of the standard entropies, and the temperature dependences of the heat capacities of the gadolinium tellurites synthesized were determined in the temperature range of 298–850 K.