Order–disorder in In 3+ perovskites: The example of A(In 2/3B″ 1/3)O 3 ( A=Ba, Sr; B″=W, U)

Abstract

We describe the preparation and structural characterization of four In-containing perovskites from neutron powder diffraction (NPD) and X-ray powder diffraction (XRPD) data. Sr 3In 2 B″O 9 and Ba(In 2/3 B″ 1/3)O 3 ( B″=W, U) were synthesized by standard ceramic procedures. The crystal structure of the W-containing perovskites and Ba(In 2/3U 1/3)O 3 have been revisited based on our high-resolution NPD and XRPD data, while for the new U-containing perovskite Sr 3In 2UO 9 the structural refinement was carried out from high-resolution XRPD data. At room temperature, the crystal structure for the two Sr phases is monoclinic, space group P2 1/ n, where the In atoms occupy two different sites Sr 2[In] 2 d [In 1/3 B″ 2/3] 2 c O 6, with a=5.7548(2) Å, b=5.7706(2) Å, c=8.1432(3) Å, β=90.01(1)° for B″=W and a=5.861(1) Å, b=5.908(1) Å, c=8.315(2) Å, β=89.98(1)° for B″=U. The two phases with A=Ba should be described in a simple cubic perovskite unit cell (S.G. Pm3¯ m) with In and B″ distributed at random at the octahedral sites, with a=4.16111(1) Å and 4.24941(1) Å for W and U compounds, respectively.