Phase transitions, dielectric, magnetic properties and valence of ions in AFe2/3W1/3O3±σ (A = Ba, Sr) multiferroic ceramics

The polycrystal multiferroic samples of BaFe2/3W1/3O3 (BFWO) and SrFe2/3W1/3O3 (SFWO) are synthesized by solid solution reaction route followed by sintering. The samples are analyzed using the methods of X-ray diffraction (XRD), dielectric, Mossbauer and X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). The XRD study reveals that BFWO possesses two crystal phases: cubic and hexagonal. SFWO is a single phase with a tetragonal symmetry. The VSM and Mossbauer spectroscopy show that both materials are ferrimagnets with magnetic phase transition temperatures T-M approximate to 300 K for BFWO and T-M approximate to 400 K for SFWO. The iron ions are in Fe3+ state. The XPS studies reveal the presence of the oxygen vacancies in the BFWO and SFWO samples which are responsible for the appearance of the tungsten ions with intermediate valences. BFWO is found to be paraelectric at room temperature. In the SFWO sample the phase transition from tetragonal (ferroelectric) to cubic (paraelectric) phase occurs in the range of 420 < T < 550 K. (C) 2018 Elsevier B.V. All rights reserved.