Electro-transport and structure of 1-2-3 HTSC single crystals with different plane defects topologies

In this work we study the structural and resistivity parameters of the 1-2-3 system HTSC single crystals by substituting yttrium to holmium and with a low (5%) aluminum doping. It was determined that in the case of non-stoichiometric samples, the structure of crystals, directly after the solution-melt growth, is close to tetragonal. In the process of additional oxygen saturation we observed a ferroelastic transition to orthorhombic phase, accompanied by the formation of a domain twin structure. The twin boundaries and the aluminum impurities are efficient scattering centers of normal carriers. At aluminum concentration y ≤ 0.5 the tweed structure is not formed.