ORDER-DISORDER STRUCTURAL PHASE-TRANSITION IN LA2-XSRXCUO4+DELTA AT 150-K

Using perturbed angular correlations of In111 in the La site, we report a structurally disordered phase in oxygen stoichiometric La2-xSrxCuO4+. So far this phase has been defined for 0x0.07, involves a reversible order-disorder transition at Td=150(20) K, and is observed by changes in the electric-field gradient (EFG). These changes involve a continuous broadening of the EFG distribution and decrease of the average EFG asymmetry parameter as T0. The new disordered phase is associated with a loss of three dimensional magnetic order in the range 0.015<x<0.018, and may be due to short-range disorder in the tilting of the CuO6 octahedra as proposed by Egami et al. © 1990 The American Physical Society.