THE STRUCTURE AND MAGNETIC CHARACTERISTICS OF A HOLMIUM-1,2,3 SUPERCONDUCTOR WITH TETRAGONAL SYMMETRY

The structure of a superconducting, single crystal of holmium-1,2,3 has been shown to be tetragonal above and below the superconducting transition temperature by a combination of X-ray, neutron and electron diffraction techniques. Structural parameters, which included site-occupancy for all atoms, have been refined at 115 and 20 K and evidence for copper as well as oxygen deficiency is presented. There is no evidence that the structure involves twinning or a superlattice. The same crystal has been shown to sustain a critical current of approximately 10(5) A/cm-2 and to exhibit a Meissner effect with T(c) = 91.5 K. Crystal data: HoBa2Cu3O7-delta. M(r) = 742.2, tetragonal, spacegroup P4/mmm. At T = 115 K, a = 3.8598(2) angstrom, c = 11.6537(9) angstrom, lambda = 1.3162 angstrom, V = 173.62(2) angstrom 3, R = 3.3% for 124 reflexions; at T = 20 K, a = 3.8592(3) angstrom, c = 11.6472(11) angstrom, lambda = 1.3162 angstrom, V = 173.47(2) angstrom 3, R = 2.7% for 124 reflexions.