Properties and phase transition of the ordered perovskite Pb2MnWO6

Abstract

Pb2MnWO6 has been synthesized and its structure determined by powder xray diffraction. This sample undergoes a first order structural phase transition at ∼445 K. This transition is coupled to a change in the electrical properties manifested by a sharp discontinuity of the dielectric permittivity at the phase transition temperature. Pb2MnWO6 is cubic paraelectric above 445 K and orthorhombic with electric ordering below such a temperature. The structural refinement reveals Pb displacements in the low temperature phase in agreement with an antiferroelectric ordering. Diferential scanning calorimetry and magnetic susceptibility measurements are also reported. The large entropy content of the transition evidences the presence of an ordering process. Pb2MnWO6 is paramagnetic in a broad temperature range in agreement with the presence of high-spin Mn2+ ions. A magnetic anomaly at 45 K may be associated with antiferromagnetic ordering of these ions that would coexist with the antiferroelectric state at very low temperature.