Effect of (Sr0.7Ca0.3)TiO3-substitution on structure, dielectric, ferroelectric, and magnetic properties of BiFeO3 ceramics

Bi1−x(Sr0.7Ca0.3)xFe1−xTixO3 ceramics were prepared by a standard solid state reaction process, and the influence of Sr/Ca ratio on structure and properties for Bi1−x(Sr,Ca)xFe1−xTixO3 system was discussed by comparing with Sr0.5Ca0.5TiO3-modified BiFeO3 ceramics. Rietveld analysis of X-ray diffraction data revealed that the crystal structure changed from rhombohedral R3c (x ≤ 0.4) to orthorhombic Pnma (x = 0.6) with Sr0.7Ca0.3TiO3 substitution, and biphasic structure (R3c + Pnma) was determined at x = 0.5, while that for Bi1−x(Sr0.5Ca0.5)xFe1−xTixO3 system was at x = 0.4. This indicated that the morphotropic phase boundary in Bi1−x(Sr,Ca)xFe1−xTixO3 system shifted toward (Sr,Ca)TiO3 side with increasing Sr/Ca ratio. The Raman spectrometric analysis and selected area electron diffraction analysis also confirmed this transition. The dielectric relaxation could be well fitted by Arrhenius law, and the different activation energies were attributed to the different origins of the dielectric relaxations with increasing temperature. The current density-field (J-E) curves indicated that the leakage current was reduced to about five orders of magnitude with Sr0.7Ca0.3TiO3 substitution. The P-E hysteresis loops obtained by three different methods indicated the enhanced ferroelectricity at x = 0.4, and it could be attributed to the decrement of leakage current. Meanwhile, the magnetization was enhanced with Sr0.7Ca0.3TiO3 substitution, and the maximum remanent magnetization was determined at x = 0.2. The enhanced magnetization originated from the partial substitution of Fe3+ by Ti4+