REDETERMINATION OF THE STRUCTURE OF THE 80-K SUPERCONDUCTOR YBA2CU4O8 BY TIME-OF-FLIGHT NEUTRON POWDER DIFFRACTION

M(r) = 745.77, orthorhombic, Ammm, a = 3.8402 (1), b = 3.8708 (1), c = 27.2309 (3) angstrom, V = 404.8 angstrom 3, D(x) = 6.119 g cm-3, Z = 2, T = 295 K, 912 reflections included, R(wp) = 5.62%, R(exp) = 3.34%. Rietveld analysis of high-resolution time-of-flight powder neutron diffraction data has been used to redetermine the structure of the 80 K superconductor YBa2Cu4O8 (the '124 phase'). The essential features of the structure previously reported have been confirmed. This study improves upon the precision of the previously reported structural parameters, obtained by powder neutron diffraction. The compound is stoichiometric, with no occupancy of the O(5) inter-chain site.