NONSTOICHIOMETRY STUDIES OF THE Y-BA-CU-O SYSTEM IN TERMS OF A REAL-SPACE SCATTERING COHERENT-POTENTIAL APPROXIMATION

A careful study of nonstoichiometry effects for the O(1), O(2), O(3), and O(4) constituents is performed using a real-space scattering cluster coherent-potential approximation method. By increasing successively the cluster size, a numerically optimal convergence of the effective scattering amplitudes can be obtained. In order to calculate spectral quantities such as the density of states (DOS) and componentlike DOS, these scattering amplitudes are then used for rather large clusters of up to 160 atoms. We find that a cluster size of about 70 atoms guarantees reliable effective scattering amplitudes. As an application the calculation of x-ray emission and x-ray photoemission spectra and of the spherical part of the Hopfield parameter as a function of nonstoichiometry is shown. © 1990 The American Physical Society.