Preparation, Magnetic Properties, and Pressure-Induced Transitions of Some MIIMIVF 6 ( MII=Ni, Pd, Cu; MIV=Pd, Pt, Sn) Complex Fluorides
Abstract
MIIMIVF6 (MII=Ni, Pd, Cu; MIV=Pd, Pt) and PdSnF6 complex fluorides have been synthesized via different preparative methods using either BrF3 as oxidizer and solvent, or solid state reactions. For MII=Ni, Pd, the phases crystallize in the rhombohedral space group Roverline3 (LiSbF6 type). Cationic ordering has been studied by X-ray diffraction and 119Sn Mössbauer resonance for PdSnF6. A lowering of symmetry has been observed when the involved divalent cation presents a Jahn-Teller configuration (CuII). Except for PdSnF6, which is paramagnetic down to 4 K, all compounds are Pd2F6-type ferromagnets at low temperature. This behavior has been related to the ordering between half-filled eg orbitals of the divalent cation and empty eg orbitals of the tetravalent cation. A drastic increase in conductivity has been observed under high pressures. In particular the insulator-semiconductor transition induced under pressure (up to 80 kbar) in Pd2F6 corresponds to a decrease of the electrical resistivity by six orders of magnitude. The assumption of an electronic transition induced under pressure from mixed oxidation states (MII+MIV) to an unique trivalent MIII oxidation state has been proposed.
- Publication:
-
Journal of Solid State Chemistry France
- Pub Date:
- December 2001
- DOI:
- 10.1006/jssc.2001.9331
- Bibcode:
- 2001JSSCh.162..333T
- Keywords:
-
- M<SUP>II</SUP>M<SUP>IV</SUP>F<SUB>6</SUB>;
- transition element fluorides;
- BrF<SUB>3</SUB>medium;
- solid state reaction;
- ferromagnetism;
- pressure-induced electronic transition;
- piezosensors.