Crystal Structure of the Orthorhombic Form of Ba₂YCu₃O_7-x at 42 K

Abstract

The crystal structure of the low-temperature form of Ba 2 YCu 3 O 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 Ba 2+ and Y 3+ 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.