Charge Transfer in YBCO Under Pressure with Bond Valence Sum Approach

Abstract

The bond valence sum method has been developed to high pressures considering B0(p) for calculating the valences of atoms. This approach has the advantages of finding a universal B0(p) for all the atoms -at least in YBCO, ability to evaluate the valency of each atom, and charge neutrality requirement of the unit cell. As a result, a new structural refinement has led to a more exact structural detail. The position of apical oxygen is found to be specially crucial for hole distribution between the superconducting CuO2 planes and Cu–O charge reservoir chains. Under pressure, the hole concentration in CuO2 planes increases, but in the Cu–O chains decreases, consistent with the pressure induced charge transfer model in HTSC. Our results resolve the anomalous behavior of dTc/dp in YBCO.