Role of BaO/SrO layers in deciding the electronic structure of Cu 0.3Co 0.7Ba 2− xSr xYCu 2O 7+ δ (CoCu-1212) x = 0, 1 and 2

Abstract

In this paper we report the change in electronic structure of Cu 0.3Co 0.7Ba 2− x Sr x YCu 2O 7+ δ with change in structural pressure. Rietveld refined X-ray diffraction (XRD) pattern shows that the samples are phase pure. Decrease in lattice parameters with increasing x, confirms replacement by Sr ion at Ba ion site. The calculated tolerance factor of the systems is in accord with lattice parameter changes. The X-ray photoelectron spectroscopy (XPS) is made to find out the variation in ionic state of Co and Cu with ionic size variation in BaO/SrO layers. Effect of the same on the electronic structure and transport properties is explored. The XPS measurement reveals that Cu is in mixed 1+/2+ state and variation in valence state is non-monotonous with increasing x. Whereas Co is in mixed 3+/4+ state and with increasing x its valence state is increasing. The observed changes in electronic structure are subject of structural changes. The resistivity measurement shows that normal state conductivity decreases with increasing x. Resistivity behaviour indicates about holes in Cu/CoO x planes taking part in charge transport. The magnetic measurement ( M– T and M– H) shows that paramagnetic nature for all the compositions. The presence of Cu ions in Cu/CoO x chains/planes results in paramagnetic behaviour.