On the inverse perovskites M3TO (M = Ca, Sr, Yb; T = Si, Ge, Sn, Pb)

Ca3SiO and seven further inverse perovskites M3TO (M = Ca, Sr, Yb; T = Si, Ge, Sn, Pb) were prepared in iron crucibles under argon by the reactions 6 M + TO2 + T = 2 M3TO, and 3 M+ TO = M3TO for Yb3PbO, respectively, at temperatures between 1123 to 1173 K. The crystal structures of all compounds were solved and refined using X-ray powder diffraction methods. Ca3SiO, Ca3GeO, Sr3SiO, Sr3GeO, Yb3SiO and Yb3GeO are orthorhombic perovskites (anti-GdFeO3-type, space group Pbnm, No. 62, Z = 4). They show slightly distorted corner-sharing OM6 octahedra that are tilted with respect to their positions in the ideal perovskite structure. The effective radii of the T4- vary significantly with M2+. Thus, these perovskites can no longer be discussed in terms of the hard-sphere model, and Goldschmidt's tolerance factor does not apply. The ideal cubic representatives Yb3SnO and Yb3PbO were refined in space group Pm (3) over barm (anti-SrTiO3 type, Z = 1).