The crystal structure of ZrCr2D≈4 at 50 K ≤ T ≤ 200 K

Abstract

Abstract Many Laves phases take up considerable amounts of hydrogen to form metallic Laves phase hydrides. They frequently undergo phase transitions driven by ordering phenomena for the hydrogen atom distribution. The cubic Laves phase ZrCr2 takes up hydrogen to form a hydride with almost four hydrogen atoms per formula unit, which undergoes a phase transition to a monoclinic modification at a critical temperature T c = 250.2 K. Its crystal structure was refined based on neutron powder diffraction data on the deuteride (ZrCr2D3.8 type [T = 1.6 K, C2/c]) at four temperatures in the range 50 K ≤ T ≤ 200 K. The monoclinic low-temperature modification features a strongly distorted square anti-prism ZrD8 and three CrD4 polyhedra with almost fully occupied deuterium sites in saddle-like, distorted tetrahedral and planar configurations. Zr–D distances are in the range 201.4(7) pm ≤ d(Zr–D) ≤ 208.5(8) pm and Cr–D distances in the range 172.9(7) pm ≤ d(Cr–D) ≤ 182.4(8) pm.