The orthorhombic structure of this material was described in terms of the shell model and associated 2-body and 3-body short-range interaction potentials. The empirical potentials were determined by fitting structural and elastic constant data. These potentials were used to calculate point-defect and small-polaron energies. An oxidation reaction between Cu+ and lattice O ions, leading to O-, was shown to be likely. The migration of O ions via a vacancy mechanism, near to the Cu-O plane, involved an estimated activation energy of the order of 0.3eV. The phonon frequencies were deduced from the potentials and were shown to agree well with experimental Raman data. Bipolarons were examined, and the O22- species was shown to be quite stable.

R.C.Baetzold: Physical Review B, 1990, 42[1], 56-66