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Dielectric and Magnetic Properties of (Bi1-xLaxFeO3)0.5(PbTiO3)0.5 Ceramics Prepared from Mechanically Synthesized Powders

Multiferroic (Bi1-xLaxFeO3)0.5(PbTiO3)0.5 ceramics was prepared from mechanical synthesized nanopowders. The XRD studies revealed the tetragonal structure and the tetragonality decreased with La content. Dielectric response of the compounds was found to contain three anomalies: 1) relaxor-like behavior due to lattice disorder (below 300 K); 2) dielectric permittivity maxima at~400 K attributed to the presence of oxygen vacancies; 3) grain boundary effect above 475 K. The Curie point at ~500 K was observed for the compound with x=0.5. The composition near the morphotropic boundary: (Bi0.8La0.2FeO3)0.5(PbTiO3)0.5 shoved the highest remnant magnetization. The irreversible magnetic properties of the (Bi1-xLaxFeO3)0.5(PbTiO3)0.5 compounds can be explained in terms of disorder induced spin-glass behavior due to random substitution of La or Pb ions for Bi sites. A sharp step in magnetization about 250 K is caused by the A-site distortion associated with tilts of FeO6 octahedra leading to modification of Fe-O-Fe angles and of antiferromagnetic coupling between magnetic Fe3+ moments.