Zijing Dong

Ferroelectric and Magnetic Properties of SrO-B2O3-SiO2 Glass-Doped BiFeO3 Ceramics

BiFeO3 ceramics doped with varying amounts of SrO-B2O3-SiO2 glass, i.e., xwt% (x = 0, 0.2, 0.4, 0.6, 0.8) have been successfully developed via a solid state reaction route. Phase identification using XRD showed that a relatively pure BiFeO3 phase could be obtained at the reaction temperature of 760° for 2h. The sintering temperature of these glass-doped BiFeO3 ceramics was controlled at about 800°, on the basis of the studies of the optimized bulk density, although the bulk density varied with the different doping levels of SrO-B2O3-SiO2 glass. The dielectric constant and dielectric loss of sintered ceramics are affected by the glass doping level, while the BiFeO3 doped with 0.6% SrO-B2O3-SiO2 glass exhibited a comparatively higher dielectric constant value and minimum dielectric loss. At x = 0.6 and 0.8, the glass-doped BiFeO3 ceramics show saturated hysteresis loops with the respective saturation polarizations of 1.2μC/cm2 and 1.4μC/cm2. Too high a glass doping level in BiFeO3 gave rise to weakened magnetic behavior.

Bi4Ti3O12 Addition in the Ultra-Broad Temperature Stability of BaTiO3-Based Ceramics

BaTiO3-Nb2O5-xBi4Ti3O12 ceramics are prepared by a conventional mixed oxide route. From the observations, the proverskite-type solid solutions are formed for x ≤ 0.075, and second phase BaBi4Ti4O15 is found for x > 0.2. The sintering temperature is reduced effectively to 1090°C. A progressive decline in ϵr max with increasing x led to near temperature-stable dielectric properties over a wide temperature range. For x = 0.15, ϵr max = 772(Δϵ/ϵ25 °C≤ 15%), from −55°C to 400°C, and tan δ≤ 0.02 from −55°C to 192°C. This work provides a roadmap to obtain a temperature-stable dielectric ceramic.

Dielectric Properties of (1-x)BaTiO3-xBaFe12O19 Composite Ceramics

The composite ceramics of (1-x)BaTiO3-xBaFe12O19 (x = 0.2, 0.4, 0.5 and 0.6) were prepared by solid state method. The phase formation and diphase microstructure of the composite samples were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that ferroelectric BaTiO3 can well coexisted with the magnetic phase BaFe12O19. The electric and dielectric properties of the obtained composites were investigated. The electrical conduction and dielectric constant of the composites increased with the increase of BaFe12O19 contents. The high values of conductivity and dielectric constant near 250°C were due to the effect of space charges that played an important role in the composites. (1-x)BaTiO3-xBaFe12O19 composites exhibited a high value of dielectric constant at low frequencies and high temperatures. At x = 0.4, the composites showed usual dielectric dispersion with increasing frequency.

Effects of different microwave calcination temperatures on the pure BiFeO 3 ceramics prepared by microwave hydrothermal method

Monophasic rhombohedral structure of high pure BiFeO₃ was successfully synthesized by microwave hydrothermal method. Then the obtained powders are processed under different microwave calcination temperatures. The results show that the microwave calcination temperature can dramatically affect the structural, microstructural, dielectric, ferroelectric and magnetic behavior of BiFeO₃ ceramics. The morphologies of the BiFeO₃ were investigated by using scanning electron microscopy. XRD and Raman results show that the BiFeO₃ ceramics calcined under 550°C, 650°C and 750°C possessed the highest purity and crystallinity. The ferroelectric hysteresis loop measurements indicate that the P_s of BiFeO₃ ceramics calcined under 750°C is around 1.4 μC/cm². Finally, the VSM results show that the BiFeO₃ ceramics exhibit a weak anti-ferromagnetic behavior and the BiFeO₃ ceramics of uncalcined and that calcined at 750°C show the maximum M_s.

A comparative study of BaTiO 3 -BaFe 12 O 19 multiferroic composites prepared by conventional and microwave sintering techniques

As one of the most important multiferroic composite systems, the 0.9BaTiO3-0.1BaFe12O19 (0.9BT-0.1BFO) composite was prepared by conventional sintering (CS) and microwave sintering (MS) techniques. High density ceramics were obtained by MS method in 70 min of cycle time, whereas it took 748 min by CS method. The phase composition and diphase microstructure of the composite samples were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was observed that ferroelectric phase BaTiO3 can well coexisted with the magnetic phase BaFe12O19, and the MS 0.9BT-0.1BFO composite showed more uniform and smaller grain size than those of CS samples. Improvement of the electric properties, including decrease in conductivity and dielectric loss was observed due to high densification, good microstructure and grain refinement in case of microwave sintering. Besides, both samples exhibited a high value of dielectric constant at low frequencies and high temperatures because of the effect of space charges that played an important role in the composites. The value of magnetization and coercive for the MS sample were significantly higher and more saturated than that of CS samples. The area for the future optimization of the sintering schedule in order to produce the dense fine-grained 0.9BT-0.1BFO multiferroic composite is also proposed.