Neutron diffraction study of phase separation in La2CuO4+delta single crystals

Single crystals of La2CuO4+delta with delta = 0.03 and delta = 0.04 have been studied in the temperature region 10 K less than or equal to T less than or equal to 293 K using a high resolution neutron diffractometer. In both crystals, the concentration of excess oxygen is inside the miscibility gap. However, the La2CuO4.03 crystal does not undergo a phase separation - homogeneous oxygen distribution was preserved over the entire temperature region studied, while in the La2CuO4.04 crystal, the phase separation phenomenon, connected with excess oxygen diffusion was observed. Analysis of the diffraction peak width as a function of interplane spacing allowed us to determine the dimensions of the coherent regions of coexisting phases: 975 +/- 22 Angstrom in the direction of the tetragonal axis of the high temperature phase, and (1460 +/- 160) Angstrom in the perpendicular direction. Our data provide direct evidence that both the oxygen-rich and oxygen-poor regions have the same Cmca space symmetry.