The structure of orthorhombic hafniates by neutron powder diffraction and perturbed-angular-correlation spectroscopy (PAC)

AHfO(3) (A = Ca, Sr and Ba) belongs to perovskite family with general formula A(2+)B(4+)O(3). The crystal structure of CaHfO(3) (CH), SrHfO(3) (SH) and BaHfO(3) (BH) at room temperature (RT) is reported, combining the results of the Rietveld method refinements using X-ray and neutron powder diffraction data and PAC spectroscopy. The structures were refined by the Rietveld Method using DBWS9411 and GSAS programs, The refinement of SH using neutron and X-ray powder pattern indicates an orthorhombic Pnma symmetry at room temperature. The hyperfine parameters of PAC spectroscopy indicate that the structure has lower-than-cubic symmetry at RT, The structures of CH and BH were refined with the Pnma and Pm (3) over bar m space group respectively. The three compounds have near regular oxygen octahedra that are characteristic of perovskites of Glazer types a(+)a(-)a(-) and a(0)a(0)a(0), for which the distortion is better related to the tilting of the octahedra.