Boutko V. Electron density and gradient electrical field in cuprats and rare-earth oxides

The thesis is devoted to application of the modified statistical method for calculating electronic properties of metal oxide crystals. The method is proved to be efficient for study of many-component crystals with the mixed type of chemical bond and a large number of atoms in the unit cell. The detail investigations with the aim of finding the electronic density distribution in Yr1-xPrxBa2Cu3O7 make it possible to remove the contradictory between structural data of neutron graphical and X-ray studies of this system. In the frameworks of the modified statistical method a good qualitative description of the gradient tensor of electrical field have been achieved both under pressure and under changes of staichuometry. The revealed change of sign of the derivative of quadruple constant respect to pressure at transition from orthorhombic to tetrorombic system explains the key role of instability of La-Sr lattice on electrical super subtle interaction. The possibility of valency changing rare-earth ions under high pressure has been carried out even though the crystal structure of the compound under investigation be unchanged. The calculations of the electron density distribution for PrO2 and Sm2O3 at different pressures and corresponding average charges of ions have been determined. Following the electro neutral principle of Polling the supposition that the change of the average charge value can be the measure of system instability. In this fashion the structural phase transition in EuO crystal induced by high pressureis is treated. The results of calculation are in good agreement with experimental data.