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

Abstract The polycrystal multiferroic samples of BaFe 2/3 W 1/3 O 3 (BFWO) and SrFe 2/3 W 1/3 O 3 (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  ≈ 300 K for BFWO and T M  ≈ 400 K for SFWO. The iron ions are in Fe 3+ 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