Dielectric and magnetic properties, and electronic structure of multiferroic perovskite PbFe0.5Ta0.5O3 and incipient ferroelectric pyrochlore Pb2Fe0.34Ta1.84O7.11 single crystals and ceramics

Multiferroic perovskite PbFe0.5Ta0.5O3 (PFT) ceramics and single crystals were synthesised using a two step "wolframite" method and grown by a flux method, respectively. Characterisation by X-ray and SEM studies showed that crystals are homogenous and posses only the perovskite phase while ceramics are less homogenous and contain small amounts of the secondary pyrochlore and Fe2O3 phases. Linear and nonlinear dielectric studies revealed two monoclinic-tetragonal and tetragonal-cubic structural phase transitions at approximately 210 K and 256 K. The ceramics exhibit relaxor-like behaviour while dielectric, pyroelectric and piezoelectric studies of the crystals undoubtedly pointed to diffuse ferroelectric phase transition. XPS studies of the crystals revealed two Fe2+ and Fe3+ valence states. The energy gap of approximately 2.8 eV was found. Magnetic studies of ceramics and crystals pointed to two magnetic phase transition, paramagnetic-antiferromagnetic at 156 K and antiferrromagnetic-spin-glass at 10 K. The pyrochlore Pb2Fe0.34Ta1.84O7.11 crystals exhibit incipient ferroelectric and paramagnetic behavior. (C) 2016 Elsevier Ltd. All rights reserved.