CRYSTAL STRUCTURE OF THE HIGH-T-C SUPERCONDUCTOR HOSR2CU2.7MO0.3O7.54 BY JOINT TIME-OF-FLIGHT NEUTRON X-RAY RIETVELD REFINEMENT

摘要

The ambient-pressure synthesis, crystal structure, and some properties of HoSr2Cu2.7Mo0.3O7.54 are described. HoSr2 Cu2.7Mo0.3O7.54 crystallizes as the tetragonal modification of the YBa2Cu3O7-delta (123) high-T-c superconductor structure, and exhibits a superconducting transition temperature of similar to 30 K. The Cu/Mo cation distribution in HoSr2Cu2.7Mo0.3O7.54 was established by means of a joint time-of-flight neutron/X-ray Rietveld refinement: The molybdenum ions substitute for copper at both the ''chain'' [Cu(1)] and square-pyramidal [Cu(2)] sites in roughly equal proportion. The chain layers [atoms Cu/Mo(1) and O(1)] show considerable static disorder in this material. Crystal data: HoSr2 Cu2.7Mo0.3O7.54 M(r) = 660.51, tetragonal, space group P4/mmm (No. 123), a = 3.83107(6) Angstrom, c = 11.5347(3) Angstrom, V = 169.296(8) Angstrom(3), Z = 1, R(p) = 4.21%, R(wp) = 5.08%, and chi(2) = 2.45. (C) 1995 Academic Press, Inc. [References: 9]