NEUTRON SPECTROSCOPIC STUDIES OF THE CRYSTAL-FIELD IN HOBA2CU3OX 6-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-7)

Inelastic neutron scattering has been employed to study in detail the full crystalline-electric-field (CEF) energy-level scheme in the groun d-state J multiplet of Ho3+ in HoBa2Cu3Ox as a function of the oxygen content x. We have been able to resolve ten ground-state transitions f or a series of samples covering the superconducting phase as well as t he semiconducting one. J mixing and intermediate coupling effects are shown to be necessary to determine unambiguously the nine and five ind ependent CEF parameters of the orthorhombic and tetragonal symmetry, r espectively. The large energy shifts and intensity changes of the obse rved CEF spectra as a function of the oxygen content x are shown to be related predominantly to a charge-transfer process from the chains to the planes, the actual charge transfer being in good agreement with r esults derived from both bond valence sum considerations for YBa2Cu3Ox and similar CEF data for ErBa2Cu3Ox.