Polarization Optical, Electric and Neutron Scattering Studies of the Perovskite Pb₂CoWO₆

Abstract

Flux grown single crystals of the elpasolite-like perovskite Pb 2 CoWO 6 have been characterized by polarized light microscopy, electric conductivity, ferroelectric polarization, elastic and inelastic neutron scattering, and DSC. A sequence of four phases is found: cubic, Fm3m (I) \overset∼298 K\longleftrightarrow monclinic, incommensurate (II) \overset∼235 K\longleftrightarrow ferroelectric (III) \overset∼9 K\longleftrightarrow ferromagnetic/ferroelectric (IV). The transitions II/III and I/II are of first order with the respective latent heats: 290 and 840 Jmole -1 Pb 2 CoWO 6 . The structure of phase I has been refined with the Rietveld system program, using the 306 K neutron diffraction data. In this phase a soft phonon mode with wave vector q along Σ has been observed and which condenses near the zone boundary point X. -Phases III and IV are probably ferroelectric.