The twin microstructure of superconducting La2CuO4+delta crystals with delt
a ranging from 0.02 to 0.04 has been studied by neutron and X-ray scanning
of the reciprocal space and high-resolution neutron diffraction. The crysta
ls studied were of two types with respect to the low-temperature diffusion
of excessive (nonstoichiometric) oxygen: those with and those without macro
scopic phase separation. It is shown that for both types of crystals, twinn
ing is accompanied by the formation of almost equivalent systems of domains
(transformational twins). The configurations of these domains provide the
formation of mainly coherent interdomain boundaries. In the La2CuO4+delta c
rystals studied, which undergo the macroscopic phase stratification during
cooling, the volume of the transient regions with the distorted structure i
s rather small, which seems to be a factor promoting diffusion of excessive
oxygen.