Study On Preparation, Structure And Properties Of Ba_1-xCa_xTiO₃Ceramics

Barium calcium titanate Ba1-xCaxTiO3ceramics (x=0.0-0.30) were prepared by sol-gel technique in this paper. Microstructure and feature of the ceramics were analyzed using X-ray diffraction (XRD) and scanning electronic microscope (SEM). We measured the electric hysteresis loops, piezoelectric response curves, piezoelectric displacement curves, permittivity vs. temperature spectrums, C-V curves, switching current curve and so on by TF Analyzer2000. The relationships of the electric properties of the Ba1-xCaxTiO3ceramic were analyzed. We measured the hysteresis loops and switching current curves. Through the analysis of electric field values and frequency on hysteresis loops and electric field values and temperature on and switching current curves, we studied the polarization switching process.It can be seen that all the samples show pure perovskite structure by XRD, suggesting that Ca diffuse into the BaTiO3lattice to form a solid solution. Also, the samples evolved from tetragonal phase to the coexistence of tetragonal phase and orthorhombic phase. We measured the hysteresis loops of Ba1-xCaxTiO3ceramics in different conditions, and compared the values of coercive field and remanent polarization. Our study showed that Pr increased fist and then decreased with sintering temperature increasing for Ba0.90Ca0.10TiO3ceramics, but we did not find a obvious law about Ec. The hysteresis loops gradually evolved slender, and the size of coercive field and remanent polarization was decreasing as the measurement temperature increasing. Before the phase change temperature, the evolution of Pr is stable, and the evolution of the hysteresis loops is not obvious. But Pr decreased promptly. In the whole evolution, the areas of the hysteresis loops were decreasing straight because higher temperature provided a higher thermal fluctuation to domain mobility. In the experiment of the sol-gel preparation of the Ba1-xCaxTiO3ceramics, the ferroelectric and piezoelectric properties were better than others when x=0.23, because it is near the solubility limit. In the room temperature, Pr was high Ec was low and the maximum piezoelectric coefficient d33can reach310pm/V. From the permittivity vs. temperature plots, the phase change temperature from tetragonal phase to cubic phase was little different compared with pure barium titanate. They were near120℃. Diffuse phase transition was observed and the diffuse phenomenon was obvious as Ca increasing. We analyzed the diffuse phase transition using a modified Curie-Weiss law. The values of y changed from1.01to1.60when x changed from0to0.23.We introduced polarization switching process and analyzed the effect of electric field value and frequency on hysteresis loops and the effect of electric field value and temperature on switching currents in Bao.9oCa0.10TiO3ceramics. Through these anlysis, we discussed the polarization switching process. These results reflected effect of frequency and electric field value on domain switching and the energy at which the polarization switching occurs was a threshold that represented the intrinsic switching barrier. Increased electric field make new domain appearance, then increased the switching currents. It was justified to consider the domains switching process as an energy process.