Order–disorder in In3+ perovskites: The example of A(In2/3B″1/3)O3 (A=Ba, Sr; B″=W, U)

We describe the preparation and structural characterization of four In-containing perovskites from neutron powder diffraction (NPD) and X-ray powder diffraction (XRPD) data. Sr3In2B″O9 and Ba(In2/3B″1/3)O3 (B″=W, U) were synthesized by standard ceramic procedures. The crystal structure of the W-containing perovskites and Ba(In2/3U1/3)O3 have been revisited based on our high-resolution NPD and XRPD data, while for the new U-containing perovskite Sr3In2UO9 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 P21/n, where the In atoms occupy two different sites Sr2[In]2d[In1/3B″2/3]2cO6, 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.