Temperature evolution of the crystal structures inLa(Mg1/2Ti1/2)O3 perovskite: relation to the microwave dielectric properties

Abstract

The crystal structure and phase transition of the perovskiteLa(Mg1/2Ti1/2)O3 (LMT) have been investigated using high-resolution neutron powder diffraction in the temperaturerange 60–1414 K. Between 1246 and 1310 K LMT undergoes the monoclinic-to-rhombohedral(P 21/n–) crossover required by Landau theory to be a first order. The temperature dependences ofthe unit cell parameters and the octahedral tilt angles suggest a discontinuous phasetransition. Specific variations of both the metal–oxygen bond lengths and theoctahedra volume in LMT are correlated with the dielectric anomalies observed in thesame temperature ranges. The uncommon dielectric behaviour in the vicinityof room temperature has been interpreted in terms of deformations of theTiO6 octahedra which change their polarizability and thereby contribute to the dielectricresponse of LMT. It is believed that in spite of a generally negligible effect, such acontribution to the relative permittivity can occur in compositions containing oxygenoctahedra as structural elements.