The relationship between critical temperature and oxygen content in YBa2Cu3O6+x

We present a model for the dependence of the superconducting critical temperature on oxygen content x in YBa2Cu3O6+x. This model is based on the necessity of losing some overlapping of the Cu-O orbitals for the appearance of superconductivity. The entering oxygen ions distort the Cu-O planes. We assume a simple model for the oxygen diffusion that consists in many stages of diffusion. Each stage is characterized by a linear TC(x) dependence with a characteristic slope that depends on the number of unit cells distorted by one oxygen ion and the angle of distortion of the planar Cu-O bonds. The theoretical dependence is in a good agreement with the experimental data. (authors)