Synthesis, X-ray and quantum-chemical investigations of double tellurites of holmium
Complex oxide phases, namely new double tellurites of holmium with the composition HoMe<sup>II</sup>TeO<sub>4.5 </sub>(where Me<sup>II</sup> - Sr, Ba) were synthesized with the ceramic technology from Ho(II), Te(IV) oxides and carbonates SrCO<sub>3</sub>, BaCO<sub>3</sub> in the range of 800-1200 ºC. For the first time the structure of tellurites was investigated by X-ray phase analysis. X-ray phase analysis was performed on the DRON-2.0 device. The intensity of the diffraction peaks was estimated on a stable scale. Radiographs of the synthesized powders were indicated by the homology method. The type of syngony, unit cell parameters, radiographic and pycnometric tellurite densities were determined. HoSrTeO<sub>4.5</sub>: a = 14.50; b = 14.05; c = 9.04Å; ρ<sub>roent. </sub>= 3.73; ρ<sub>pycn</sub>. = 3.59 ± 0.04 g/cm<sup>3</sup>; HoBaTeO<sub>4.5</sub>: a = 12.10; b = 5.49; c = 11.49Å; ρ<sub>roent.</sub> = 4.07; ρ<sub>pycn. </sub>= 3.93 ± 0.06 g/cm<sup>3</sup>. The correctness of the results of indexing radiographs of tellurites is confirmed by the good agreement between the experimental and calculated values of the reciprocal values of the squares of interplanar distances (10<sup>4</sup>/ d <sup>2</sup>) and the consistency of the values of X-ray and pycnometric densities. It has been established that holmium tellurites are synthesized in monoclinic syngony and have a perovskite-like structure. Quantum-chemical calculations of the stable geometry of the synthesized tellurites were carried out using the Gaussian-2009 software package with the help of the UFF molecular method. In this case, equilibrium internuclear distances (long bonds) and bond angles are the parameters. Based on the results of quantum chemical calculations, models of the geometric structure of new holmium tellurites are presented.