Crystal Structure of the Orthorhombic Form of Ba2YCu3O7-x at 42 K

Abstract

The crystal structure of the low-temperature form of Ba₂YCu₃O_7-x at 42 K was refined by the Rietveld analysis of TOF neutron powder diffraction data. This material is orthorhombic with space group Pmmm and lattice constants a=3.8800 Å, b=3.8122 Å, and c=11.6264 Å. It has an oxygen-deficient triperovskite structure in which oxygen atomson a z=1/2 plane are lacking completely, two oxygen sites on a z=0 plane are partially occupied, and Ba²⁺ and Y³⁺ ions are ordered in a [Ba-Y-Ba]_∞ sequence along the c axis. The occupation factors of oxygen at (1/2, 0, 0) and (0, 1/2, 0) are 0.84 and 0.05, respectively.