The twin structures of superconducting La2CuO4+δ crystals, where δ ranged from 0.02 to 0.04, were studied by means of neutron and X-ray scanning and high-resolution neutron diffraction. The crystals were of 2 types, with or without macroscopic phase separation, with regard to the low-temperature diffusion of excess O. It was shown that, in both types of crystal, twinning was accompanied by the formation of almost equivalent systems of transformational twins. The configurations of these domains permitted the formation of largely coherent inter-domain boundaries. In the present crystals, which underwent macroscopic phase stratification during cooling, the volume of transient regions with a distorted structure was rather small. This seemed to be a factor which promoted the diffusion of excess O.

Twinned La2CuO4 Structure. A.M.Balagurov, A.I.Beskrovnii, V.J.Pomyakushin, V.G.Simkin, B.S.Bagautdinov, V.S.Shekhtman, A.A.Zakharov: Kristallografiya, 1999, 44[1], 74-82 (Crystallography Reports, 1999, 44[1], 69-77)