It was pointed out that photo-emission and inverse photo-emission spectra clearly revealed the existence of doping-induced states within the antiferromagnetic gap of such oxides. Experimental data indicated that these states had a predominant O character, and resulted from a transfer of density of states from the lower and upper Hubbard bands. They also seemed to be related to localized orbitals. It was noted that it was important to determine the physical nature of these states, and whether the states in the gap resulted only from strong correlations or from a combination of strong correlation and O disorder. It was shown here that structural defects such as excess O and O vacancies in the CuO2 plane could cause deep impurity states in the gap which had approximately the same characteristics as those observed. Moreover, it was found that Cu disorder did not cause such states in the gap. These simple results were interesting with regard to clarification of the physical origin of these states.

W.Zhang, K.H.Bennemann: Physics Letters A, 1994, 196[1-2], 113-9

Percolative Diffusion of a Dumb-Bell Interstitial Defect on a Face-Centered Cubic Lattice - Calculation of a Percolation Threshold by Use of a Series Method (see under Diffusion Processes)

Computer Simulation of Chemical Diffusion in a Binary Alloy with an Equilibrium Concentration of Vacancies (see under Diffusion Processes)

Diffusion of Vacancy-Impurity Pairs in Crystalline Solids, Studied by Means of Monte Carlo Simulation (see under Diffusion Processes)

Thermodynamics of Atom-Vacancy Solid Solutions, as Deduced from a Self-Diffusion Arrhenius Plot (see under Diffusion Processes)