Study on magnetoelectric properties of Ni 0.5 Zn 0.5 Fe 2 O 4 /Ba 0.8 Sr 0.2 TiO 3 composite ceramics based on Bi 2 O 3 as combustion aid

Ni 0.5 Zn 0.5 Fe 2 O 4 /Ba 0.8 Sr 0.2 TiO 3 (NZFO/BST) composite ceramics with different additions of Bi 2 O 3 (0%, 1%, 3%, and 5% wt) were synthesized via the solid-phase sintering method. XRD analysis indicates that the composite ceramics show bi-phase structure, without apparent secondly phases can be observed. SEM images show that all the specimens have relative dense structure, the grain size is in the range 1–2 μm. A certain amount of Bi 2 O 3 is beneficial to grain growth, the average grain size of NZFO/BST ceramics increases from 179 to 297 nm when the concentration of Bi 2 O 3 is 0 and 3%, respectively. EDS results indicate that the distribution of NZFO phase and BST phase is not uniform. The sample NZFO/BST-3%Bi 2 O 3 not only has the largest dielectric constant ( ε r ) in the whole temperature range (25–500 °C), but also presents the smallest dielectric loss (tan δ ) at high temperature region (> 400 °C), and the maximum tan δ value is less than 0.4 for all the samples, indicating excellent dielectric performance. Compared with other samples, the specimen NZFO/BST-3%Bi 2 O 3 has the largest remnant polarization (~ 1.14 μC/cm 2 ). The sample NZFO/BST-3%Bi 2 O 3 has the largest leakage current density, while the ceramic NZFO/BST-5%Bi 2 O 3 presents the opposite behavior, the value of leakage current of the sample NZFO/BST-3%Bi 2 O 3 is about 7 times larger than that of the specimen NZFO/BST-5%Bi 2 O. All the composite ceramics show soft magnetic behavior, since Bi 2 O 3 is a non-magnetic phase, addition of Bi 2 O 3 will dilute the magnetic moment per unit volume so as to decrease the magnetic properties of the ceramics. The sample NZFO/BST-3%Bi 2 O 3 has the second largest saturation magnetization ( M r ) of 11.27 emu/g and the smallest coercive field ( H C ) ~ 3.54 Oe. All the samples show strong magnetoelectric coupling effect, the highest magnetoelectric coupling coefficient is ~ 47 Vcm −1 Oe −1 , which was obtained in the sample without addition of Bi 2 O 3 . In short, the addition of Bi 2 O 3 not only affects the structure of composite ceramics, but also plays an important role in affecting the magnetoelectric performance.