Study on magnetoelectric properties of Ni0.5Zn0.5Fe2O4/Ba0.8Sr0.2TiO3 composite ceramics based on Bi2O3 as combustion aid

Ni_0.5Zn_0.5Fe₂O₄/Ba_0.8Sr_0.2TiO₃ (NZFO/BST) composite ceramics with different additions of Bi₂O₃ (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 Bi₂O₃ is beneficial to grain growth, the average grain size of NZFO/BST ceramics increases from 179 to 297 nm when the concentration of Bi₂O₃ 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%Bi₂O₃ not only has the largest dielectric constant (ε_r) in the whole temperature range (25–500 °C), but also presents the smallest dielectric loss (tanδ) at high temperature region (> 400 °C), and the maximum tanδ value is less than 0.4 for all the samples, indicating excellent dielectric performance. Compared with other samples, the specimen NZFO/BST-3%Bi₂O₃ has the largest remnant polarization (~ 1.14 μC/cm²). The sample NZFO/BST-3%Bi₂O₃ has the largest leakage current density, while the ceramic NZFO/BST-5%Bi₂O₃ presents the opposite behavior, the value of leakage current of the sample NZFO/BST-3%Bi₂O₃ is about 7 times larger than that of the specimen NZFO/BST-5%Bi₂O. All the composite ceramics show soft magnetic behavior, since Bi₂O₃ is a non-magnetic phase, addition of Bi₂O₃ will dilute the magnetic moment per unit volume so as to decrease the magnetic properties of the ceramics. The sample NZFO/BST-3%Bi₂O₃ 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⁻¹Oe⁻¹, which was obtained in the sample without addition of Bi₂O₃. In short, the addition of Bi₂O₃ not only affects the structure of composite ceramics, but also plays an important role in affecting the magnetoelectric performance.