Crystal structure of β-CaNi 5D 0.77 by rietveld analysis of neutron powder-diffraction data

Abstract

β-CaNi 5D 0.77 is orthorhombic ( a = 8.6033(13) b = 5.0810(9) c = 7.8557(15)Å, Pmcm, Z = 4, D x = 6.48 g cm −3, V = 343.4Å 3, FW = 1339.8 amu. Rietveld analysis of a neutron powder-diffraction pattern shows that D atoms occupy the centers of [Ni 4Ca 2] square dipyramids (“octahedra”) linked through the Ca atoms at opposite apices and forming chains. About 80% of the deuterium atoms occupy fairly regular sites (DNi = 1.53, 1.80, 1.86, 1.86 Å; DCa = 2.42, 2.45 Å). The remaining 20% occupy very distorted sites (DNi = 1.21, 1.38, 2.07, 2.07 Å; DCa = 2.54, 2.60 Å). The average DD distance in a chain is 4.3 Å.