On the Crystal Structure of BaTbO3

The structure of perovskite-like BaTbO3 has been reinvestigated by high-resolution powder neutron diffraction at room temperature using HRPD at the ISIS Facility. It has been shown that neither the space group R c nor Pnma describes correctly its structure. The profile refinement has demonstrated that BaTbO3 is tetragonal, space group I4/mcm, with the cell parameters a=6.04832(4) ? and c=8.58569(10) ?. This result is in agreement with the conclusions of Woodward, that the space group R c is unlikely adopted by the A2+B4+O3-type perovskites.