INFLUENCE OF STRUCTURAL-CHANGES ON ELECTRONIC STATES IN THE 1-2-3 HTSC SYSTEM

The structural and electronic properties of the compounds YBa2Cu3O6+x, PrBa2Cu3O6+x, Y0.7Ca0.3Ba2Cu3O6+x and YBa2Cu2.7Zn0.3O6+x have been investigated by X-ray diffraction, electrical resistivity and Hall effect measurements versus oxygen content (0 less-than-or-equal-to x less-than-or-equal-to 1). It was found that the electronic state changes for different representatives of the 1-2-3 system caused by oxygen ordering are of the same character in spite of the difference in electronic properties of these compounds. The results show that the influence of oxygen ordering on superconducting and metal-insulator transitions is to increase the number of mobile holes. But the influence of structure symmetry change on the mechanism of superconductivity was not observed. The behavior of structural and electronic properties in the 1-2-3 system under changing of oxygen stoichiometry was analyzed within the framework of the Landau theory for the oxygen ordering closely connected with charge transfer between CuO2 and CuOx planes.