Some Resistive Properties of Novel Oxide Conductors Cu28-m Pbm-x Ax-p Mp Oy (A, M = Ba, Sr, Ag)

Oxide conductors have been prepared starting from the composition with the unit cell formula Cu24Pb4032 which corresponds to the compound with NaCl type structure referred to in the literature as mineral murdochite. The Pb4+ ions are partly substituted by ions of lower valency like Sr2+, Ba2+ and this results in oxidation of copper (Cu2+ Cu3+) which in turn esta blishes mixed valency states (MVS). The general unit cell formula Cu28-m Pbm_x Ax_p Mp Oy can be proposed and variation of parameters m, p, x with permutation of ions A and M results in a pronounced conductivity of samples at room temperature (RT). Some of them exhibit downturn of the electrical resistance (DER) by cooling from 230 K — 350 K. Since the electrical resistance is enhanced by application of higher current densities in the temperature range where the DER occurs, metallic derivatives of murdochite obtained by substitution of Cu and Pb can be used as interesting candidates for the searching of superconductivity (SC) at T > 200 K