Cationic ordering and role of the B-site lanthanide(III) and molybdenum(V) cations on the structure and magnetism of double perovskites Sr2LnMoO6

We describe the preparation, crystal structure determination and magnetic properties of a new series of ordered double perovskite oxides Sr2LnMoO6 (Ln = Eu, Gd, Dy, Ho, Er, Yb) with Mo5+ and Ln3+ electronic configurations. These compounds have been obtained by solid state reaction under reducing conditions in order to stabilize Mo5+ cations. Structural characterization by XRPD and NPD was performed when Ln = Ho, Er, Yb and just XRPD for absorbing Ln = Eu, Gd, Dy. At room temperature, an excellent Rietveld fit was obtained for all the samples in a monoclinic symmetry, space group P21/n, with long-range ordering of Ln and Mo atoms. Magnetic susceptibility measurements show that some of these materials present magnetic ordering below 25 K and the determined effective magnetic moments are consistent with those expected for the pair Ln3+-Mo5+. All the phases have negative dominance of the Weiss temperature indicating dominance of antiferromagnetic interactions.S.A.L. and C.A.L. thank CONICET fellowships. J.C.P. and RDS thanks the CONICET (Projects PIP 01360/08, PIP 00912/12 and PIP 00450/11) and SECyT-UNSL (Projects PROICO 7707 and PROICO 2-1612). J.C.P. and R.D.S are members of CONICET. J.A.A. acknowledges the financial support of the Spanish Ministry of Science and Innovation to the project MAT2010-16404

Localization and Impact of Pb-Non-Bonded Electronic Pair on the Crystal and Electronic Structure of Pb2YSbO6

The synthesis and crystal structure evolution of the double perovskite Pb2YSbO6 is reported for the first time. The structure has been analyzed in the temperature range between 100 and 500 K by using a combination of synchrotron and neutron powder diffraction. This compound shows two consecutive first order phase transformations as previously observed for a subgroup of Pb2RSbO6 perovkites (R = rare earths). The thermodynamic parameters associated with the phase transitions were calculated using differential scanning calorimetry (DSC), and the role of the diverse cations of the structure was studied from DFT calculations for the room temperature polymorph. The crystal structure evolves from a C2/c monoclinic structure (a–b–b– tilting system in Glazer’s notation) to another monoclinic P21/n (a–a–b+) phase with an incommensurate modulation and finally to a cubic Fm3̅m perovskite (a0a0a0). The highly distorted nature of the room temperature crystal structure seems to be driven by the polarization of the Pb lone pair which shows a marked local effect in the atomic spatial arrangements. Moreover, the lone pairs have been localized from DFT calculations and show an antiferroelectric ordering along the b monoclinic axis.Fil: Larregola, Sebastian Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Alonso, José A.. Instituto de Ciencia de Materiales de Madrid; EspañaFil: de la Peña O'Shea, Victor A.. IMDEA Energy Institute; EspañaFil: Sheptyakov, Denis. Laboratory for Neutron Scattering; SuizaFil: Pomjakushin, Vladimir. Paul Scherrer Institute; SuizaFil: Fernandez Díaz, María T.. Institut Max Von Laue Paul Langevin; FranciaFil: Pedregosa, Jose Carmelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentin