An Equation of State for High-Temperature Superconductors

In the present paper the expression of cohesive energy and the bulk modulus as a function of volume are formulated for high-Tc copper oxide superconductors. The model employed consists of long-range electrostatic Coulomb interaction and short-range overlap repulsion. The short-range overlap potential is considered in the Born-Landé inverse power form. The model parameters of the Born-Landé model are calculated from the equilibrium condition and data of bulk modulus at room temperature. The computed values of the pressure derivatives of the bulk modulus atP = 0 and the values of the bulk modulus are found to be in very close agreement with experimental values for high-Tc copper oxide and their nonsuperconducting parent compounds. It is also found that the quantityAU/U( V0) of these compounds increases with increasing hydrostatic pressure.