Peculiarities of crystal structure and crystal-field excitations in "1212" AlSr2RCu2O7 (R = Y, Er)

Investigation of substitution effects for various sites in the "1212" perovskite-like systems with a general formula R(Sr,Ba)(2)(Cu3 - yMy)O7 - delta (M = Fe, Co, Hg, Al, Ga, Zn, and Ni and R = rare earth) is of great interest in connection with the problem of high-ir, superconductivity. The crystal structure of the "1212" AlSr2RCu2O7 (R = Y, Er) compounds has been studied using high-resolution neutron powder and electron microscope diffraction measurements. Inelastic neutron scattering has been employed to search for crystalline-electric-field (CEF) transitions. The structural results yield evidence for superlattice ordering with orthorhombic symmetry (Pm2a space group). The CEF spectrum turns out to be a superposition of two components, which can be related to a local inhomogeneity of charge states within the CuO2 planes. (C) 2000 Elsevier Science B.V. All rights reserved.