Preparation Of (Ba 0.85 Ca 0.15 )(Zr 0.1 Ti 0.9 )O 3 -based Piezoelectric Ceramics By Sol-gel Method And Its Low-temperature Sintering Behavior

The (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ?abbreviated as BCZT? ceramics, as one type of BaTiO3-based ceramics, regarded as one of the most promising lead-free piezoelectric ceramics. Owing to its excellent dielectric, piezoelectric and ferroelectric properties, it intrigues the research interest of most scientists for replacing lead-containing materials. As we know, the high d33 is obtained in BCZT by optimizing sintering temperature at 1540?, which limited its application by a large extent. Nevertheless, the lead zirconate titanate ?PZT? ceramics are not environment friendly due to the lead oxide toxicity, and their industrial applications have been gradually prohibited in recent years. Therefore, it is meaningful to have a deeper research on the BCZT ceramics.Recently, a lot of works have been carried out to improving the sinterability and electrical properties of BCZT ceramics by tuning the Ba/Ca or Zr/Ti, doping metal oxide, the sintering aids additive, snd designing BCZT-ABO3 binary system.. According to previous research works, it is known that very few literatures have reported on the synthesis of BCZT using wet chemical synthesis techniques. Generally, as one of the wet chemical methods, the sol-gel process has shown considerable advantages including excellent chemical stoichiometry, compositional homogeneity, and lowering crystallization temperature due to the mixing of liquid precursors on the molecular level. Furthermore, it could modify the microstructure and to some extent could further improve the electric properties of ceramics. Based on above analysis, the main purpose of this research is to reduce the calcining and sintering temperature of BCZT ceramics. In this work, (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃, (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃:xCu²⁺?x= 1%,1.5%,2%,2.5%? and (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃:xZn²⁺?x= 1%,2%,3%,4%,5%? ceramics were prepared by the sol-gel method. The influence of coagulating conditions ?concentration of Ti and acetic acid, bathing temperature?, calcining and sintering temperatures on phase structure, microstructure, dielectric, ferroelectric and piezoelectric properties of ceramics were investigated in detail. The main results of the study were as follows:1. (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramics were separately synthesizes by the sol-gel method ?BCZT-SG? and solid-state method ?BCZT-SS?. It was found that Ti concentration of reaction solution, acetic acid concentration and bathing temperatures of sol substantially affect ferroelectric and dielectric properties of BCZT ceramics. The optimum parameters for the precursor conditions of BCZT ceramics by the sol-gel method are as follows:the Ti concentration is 0.5 mol/L, the acetic acid concentration is 40%, the bathing temperature is 50?. Through systematically studying the effect of calcining and sintering temperatures on phase structure, microstructure, ferroelectric and dielectric properties of BCZT ceramics, the results indicates that BCZT-SG ceramics with the highest density and fine-grained microstructure calcined at 1000? and sintered at 1420? exhibited outstanding electrical properties, which are as follow:Pr= 11.9 ?C/cm², Ec= 1.76 kV/cm,?m= 14445, tan?= 0.013, kp= 0.55, d33= 558 pC/N. Compared BCZT ceramics prepared by solid-state method ?SS?, BCZT-SG ceramics showed much more excellent performance than those of BCZT-SS ceramics.2. (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃:xCu²⁺?x= 1%,1.5%,2%,2.5%? ceramics were synthesizeeds by the sol-gel method. The optimum parameters for the precursor conditions of BCZT:xCu²⁺ ceramics by the sol-gel method are as follows:the Ti concentration is 0.55 mol/L, the acetic acid concentration is 36%, the bathing temperature is 50?. By Cu²⁺ additive, the calcining temperature of samples was damatically decrease, x=1%is 1270?, x= 1.5% is 1280?, x= 2% is 1230?, x= 2.5% is 1210?. Through systematically studying the effect of sintering temperatures on phase structure, microstructure, ferroelectric and dielectric properties of BCZT:xCu²⁺?x=1%,1.5%,2%, 2.5%? ceramics, the optimum sintering condition was obtained. Among these ceramics, the BCZT: 2%Cu²⁺ ceramics exhibitd good electric properties:Pr= 5.58 ?C/cm², Ec= 1.55 kV/cm, ?m= 12112, tan?= 0.026, kp= 0.47, d33= 382 pC/N. Our results revealed that the addition of Cu²⁺significantly improved the sinterability of BCZT ceramics and the sintering temperature decrease from 1420? to 1230?.3. (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃:*Zn²⁺?x=1%,2%,3%,4%,5%? ceramics were prepared by the sol-gel method. The calcining temperature of samples was evidently depress after Zn²⁺ additive, x= 1% is 1360?, x=2% is 1340?, x=3% is 1320?, x= 4% is 1300?, x=5% is 1280?. Through systematical research on the effect of different sintering temperatures on phase structure, microstructure, ferroelectric and dielectric properties of BCZT:xZn²⁺?x=1%,2%,3%,4%,5%? ceramics, the optimum sintering condition was achieved. Among these ceramics, the BCZT-0.03Zn²⁺ceramics exhibited good electric properties:Pr= 6.62?C/cm², Ec= 2.12 kV/cm, ?m= 12261, tan?= 0.013, kp= 0.50,d33=476 pC/N. Results revealed that the addition of Zn²⁺ significantly improves the sinterability of BCZT ceramicsand the sintering temperature decrease from 1420? to 1320?.4. The comparison of the phase structure, microstructure, ferroelectric and dielectric properties of BCZT, BCZT:2%Cu²⁺ and BCZT:3%Zn²⁺ ceramics by the sol-gel method were performed in detail. The results showed that the addition of Cu²⁺ and Zn²⁺ can significantly lower the calcining and sintering temperatures of BCZT ceramics. Meanwhile, after Cu²⁺ and Zn²⁺ addition, the samples also show a relatively good piezoelectric, ferroelectric and dielectric properties.