Correlation Between the Effects of Conductivity and Superconductivity of YBCO with the Features of the Crystal Structure
The research has shown that the processes of occurrence and relaxation of elementary charge excitations are related to the peculiarities of changes in the parameters of the crystal structure of YBa2Cu3O7-d (YBCO), which are caused not only by the degree of hole doping, but also due to decrease in temperature chaotization - of anharmonicity of atomic vibrations, on average over the lattice. The research is based on theoretical concepts and information resulting from the analysis of empirical data and recognized provisions on the conductivity of materials. The structure of YBCO unit cells in three main modifications corresponding to oxygen stoichiometry with indices 7-d = 6, 6.5 and 7 is considered in detail, as well as the charges the base blocks and the conduction block, with purely ionic bonds between the atoms in these blocks. We consider the issue of the supply of holes in the Cu(2)O(2)O(3) plane from the Cu(1)O(1) chain, as a result of the relative displacements of ions along the c axis and an increase in the hole concentration in the Cu(2)O(2 )O(3), due to the appearance of the dielectric screening effect. It is shown that local and generalized charge excitations providing this effect are capable of responding to external influences, just like Fermi electrons in metals. The question of the applicability of the drift and diffusion concepts when interpreting the formation of conductivity in YBCO, where there are no "free" charge carriers, as in metals and semiconductors, is discussed. It is shown that the contradiction associated with the direct and with the inverse dependence of the relaxation time on the conductivity within the drift and diffusion concepts does not arise if we take into account the thermal volumetric deformation of the lattice, which is usually neglected at the theoretical interpretation.