A comparative study on the dielectric and multiferroic properties of Co0.5Zn0.5Fe2O4/Ba0.8Sr0.2TiO3 composite ceramics

Co0.5Zn0.5Fe2O4/Ba0.8Sr0.2TiO3 (CZFO/BST) composite ceramics with different molar ratios (1:3, 1:2, 1:1, 2:1 and 3:1) were prepared by combining chemical co-precipitation and sol-gel method. Effects of molar ratio on the microstructure, dielectric and multiferroic properties were investigated. The formation of the individual phases and the composites was confirmed by XRD results and small amount of secondary phase (Ba2Fe2Ti4O13) was observed. The grain sizes of magnetic (CZFO) and ferroelectric phase (BST), measured by SEM, were about 5 µm and 0.5 µm, respectively. The sample with molar ratio (1:2) has the largest dielectric constant, while the sample with molar ratio (3:1) shows the lowest dielectric constant. A distinct loss peak can be observed for all the samples. Both the peak position and peak intensity increase with the frequency, indicating relaxation polarization process generated by space charge or interface polarization. The ceramics with molar ratio (1:1) shows the smallest leakage current (∼ 10−7 A/cm at 1.5 kV/cm), while the leakage current (∼ 10−5 A/cm at 1.5 kV/cm) of the sample with molar ratio (3:1) is the largest. The ferroelectric hysteresis loop is not apparent due to the low Curie temperature of the ferroelectric phase, but the sample with molar ratio (2:1) shows the best ferroelectric properties. It was found that with the increase of CZFO content, the values of saturation (Ms) and remnant (Mr) magnetization increase at first and then decrease. The sample with molar ratio (3:1) has the maximum Ms value (about 50.34 emu/g), while the sample with molar ratio (1:2) shows the minimal Mr value (about 0.46 emu/g). This anomalous magnetic property is induced by the interface interaction between the two phases.