| Bismuth layer-structured compounds have been given more attention due to their high Curie temperature Tc, low dielectric coefficients and low dielectric loss. The bismuth layer-structured lead-free piezoelectric ceramic materials have the wide application prospects in high temperature and high frequency situations, ferroelectric storage, energy converter, filter and so on. However, because of the rotation of the spontaneous polarization is restricted to the a-b planar plane, the piezoelectric property of the ceramics is low. High temperature bismuth layer-structured piezoelectric materials Bi4Ti3O12 (Tc-675 ℃) were chosen and investigated in this thesis. We engaged in the improvement of the piezoelectric activity in Bi4Ti3O12 ceramics. In order to obtain more excellent performance and higher practical value, we use the traditional preparation and mixed oxide processing route procedure to fabricated modified Bi4Ti3O12 piezoelectric ceramic materials.Firstly, bismuth layer-structured ceramics (1-x)Bi4Ti3O12-xLiNbO3(BTO-LN, x=0,0.05,0.10,0.15,0.20,0.30) were prepared by the solid state reaction method. The effects LiNbO3 addition on the phase, microstructure and electrical properties of the ceramics have been investigated in detail. The results indicate that the ceramics with x≤ 0.15 possess a single bismuth oxide layered structure, the addition of LiNbO3 enhanced the grain growth of the ceramics and the Tc decreases gradually. With the increasing of the amount of LN, piezoelectric properties d33 increased then decreased, dielectric loss decreased then increased. When x= 0.15, the ceramic shows the highest d33 of 12 pC/N with minimum tan δ(～ 0.45%).Secondly, in order to improve the piezoelectric properties, we use CeO2 modify the 0.85Bi4Ti3O12-0.15LiNbO3. The effects of cerium addition on the microstructure and electrical properties of ceramics were investigated in details. The ceramics possessed a pure three-layer Aurivillius-type structure. The piezoelectric properties of 0.85Bi4Ti3O12-0.15LiNbO3 based ceramics were significantly enhanced and the dielectric loss decreased after cerium doping. The Curie temperature Tc gradually decreased from 653 to 617℃ with the increasing of the cerium content. The piezoelectric constant d33, dielectric loss tan δ and mechanical quality factor Qm for the BTO-LN ceramics with 0.75% CeO2 modification were found to be 25 pC/N,0.10%, 2895, respectively, together with the high Tc(617 ℃) and stable piezoelectric properties, which demonstrated that the cerium modified BTO-LN piezoelectric ceramics are the promising candidate for high-temperature applications.Finally, the cerium modified 0.85Bi4Ti3O12-0.15LiNbO3-0.75%wtCeO2 (BTO-LN-0.75Ce) piezoelectric ceramics were synthesized by using a conventional solid state processing. The effects of different temperatures and frequencies on the electrical properties of ceramics were investigated in details. It was found that both the real (ε’) and the imaginary (ε") parts of permittivity showed dispersion at low frequencies. With the increasing of frequency, the values of the real (Z’) part of impedance (Z) decreased, but the values of the imaginary (Z") part firstly increased and then decreased. The Cole-Cole plots showed the grain interior made a major contribution to the electrical conduction process, which could be viewed as a parallel RC equivalent circuit. The semicircles became smaller and smaller arising from increasing temperatures, which indicated that the impedance decreased with the increase in temperatures. Stabilized conductivity was observed in the low frequency region at high temperatures. Conductivity obeyed the Arrhenius law, which indicated the thermal activation of the process. The grain activation energy Ea1(g) of BTO-LN-0.75Ce was lower than Ea2(g) of BTO-LN, the values were 1.59eV and 1.75eV, respectively. |
PDF Full Text Request