SINGLE-CRYSTAL DIFFRACTION STUDY OF PHASE-SEPARATION IN LA2CUO4+DELTA

Single crystals of La2CuO4+delta with delta = 0.03 and delta = 0.04 ha ve been studied in the temperature range 10 K less than or equal to T less than or equal to 293 K using high-resolution neutron diffractomet er. In both crystals, the concentration of excess oxygen is inside the miscibility gap. However, the La2CuO4.03 crystal does not undergo a p hase separation - homogeneous oxygen distribution was preserved over t he entire temperature region studied - while in the La2CUO4.04 crystal , the phase separation phenomenon, connected with excess oxygen diffus ion was observed. Our data provide direct evidence that both the oxyge n-rich and oxygen-poor regions have the same Cmca space symmetry. The dimensions of the coherent regions of coexisting phases are (975 +/- 2 2)Angstrom in the (0 1 0) direction, and (1460 +/- 160) Angstrom in th e perpendicular direction.