title: High-temperature behavior and polymorphism in novel members of the perovskite family Pb2LnSbO6 (Ln=Ho, Er, Yb, Lu).
abstract: The synthesis, crystal structure, and dielectric properties of four novel members of the family of double perovskites Pb(2)LnSbO(6) are described. The room-temperature crystal structures were refined from neutron powder diffraction (NPD) data in the monoclinic C2/c (No. 15) space group. They contain a completely ordered array of alternating LnO(6) and SbO(6) octahedra sharing corners, tilted in antiphase along the three pseudocubic axes, with a a(-)b(-)b(-) tilting scheme, which is very unusual in the crystallochemistry of perovskites. The lead atoms occupy highly asymmetric voids with 8-fold coordination due to the stereoactivity of the Pb(2+) electron lone-pair. Several trends are observed for the entire family of compounds upon heating. The Ln = Lu, Yb, and Er oxides display three successive phase transitions in a narrow temperature range, as shown by differential scanning calorimetry (DSC) data, while the Ln = Ho shows only two transitions. Different crystal structure evolutions have been found from temperature-dependent NPD and DSC, following the space-group sequence C2/c → P2(1)/n → R ̅3 → Fm ̅3m for Ln = Lu and Yb, the sequence C2/c → unknown → P2(1)/n → Fm ̅3m for Ln = Er, and C2/c → P2(1)/n → Fm ̅3m for Ln = Ho. The Ln/Sb long-range ordering is preserved across the consecutive phase transitions. Dielectric permittivity measurements indicate the presence of a paraelectric/antiferroelectric transition (associated with the last structural transition), as suggested by the negative Curie temperature from the Curie-Weiss fit of the reciprocal permittivity.
authors: Área de Química General e Inorgánica Dr. Gabino F. Puelles, Departamento de Química, Facultad de Química, Bioquímica, y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis, Argentina.
authors: Sebastián A
authors: SA
authors: Larrégola
authors: José A
authors: JA
authors: Alonso
authors: Denis
authors: D
authors: Sheptyakov
authors: Miguel
authors: M
authors: Algueró
authors: Angel
authors: A
authors: Muñoz
authors: Vladimir
authors: V
authors: Pomjakushin
authors: José C
authors: JC
authors: Pedregosa