| Sodium bismuth titanate (Bi0.5Na0.5)TiO3(BNT), which has strong ferroelectric properties at room temperature, is a kind of A-site perovskite-type ferroelectric with relatively high Curie temperature 320 oC and large remanent polarization 38μC/cm2. Therefore, BNT-based lead-free ceramic has been considered to be one of the most promising candidate materials for lead-based ceramics at the advantages of excellent electrical properties and environment friendly. In this paper, lead-free (1-x)(0.968Bi0.5Na0.5TiO3-0.032BaTiO3)-xBi0.5K0.5TiO3 (BNBKTx) ternary system piezoelectric ceramics were desigined by linear combination rule, and optimized by doping and reducing the sintering temperature.BNBKTx ceramics were prepared by conventional solid-state reaction method. The XRD results show that all BNBKTx ceramics have pure pervoskite structure and the MPB is loacated at the composition range of 0.08≤x≤0.10. The electrical properties and phase diffusion of the BNBKTx ceramics near MPB were studied. The results show that BNBKT9 has lower coercivity field near MPB with Ec=1.98kV/mm and the best piezoelectric properties of d33=162p C/N, kp=31%. It is also found that the BNBKTx ceramics are typical relaxor ferroelectrics, whose degree of diffuseness are increasing with the increase of BKT.The microstructures and electric properties of BNBKT9 doped by Sb2O3 were investigated. XRD results indicate that as Sb2O3 is doped with x < 0.02, BNBKT9-xSb ceramics owned the same pure perovskite structure as the matrix; the second phase developed at the range of 0.02≤x≤0.04. Sb2O3 seems to act as "donor" and "acceptor" because of its variable valences, which can change the electric properties to"soft"or"hard". When x≤0.005, the piezoelectric constant d33 and the electromechanical coupling coefficient kp increase with the increase of Sb2O3 content, but the mechanical quality factor Qm decreases, exhibiting characteristics of"soft"additives. On the contary, a hard property was induced when x>0.005 at which Qm increases and kp decreases. The ferroelectric and piezoelectric properties of BNBKT9-xSb ceramics with excess addition of Sb2O3 (0.02≤x≤0.04) dropped dramatically, which could be related to the formation of antiferroelectric micro-domain at room tempature. The low-temperature sintering and electric properties of BNBKT9-0.5Sb ceramics aidded by CuO were studied. The sintering temperature can be reduced to about 1060°C, which is lower than that of the matrix, and the density of doped samples is up to 98% of theoretical value. It is due to a lower melting point of CuO, which produces a liquid phase during sintering. The dielectric loss tanδof ceramics increases with the CuO addition, which indicated that the ionic conductivity is increasing. The interfacial polarization of ceramics containing higher content of CuO contributed to the increasing of dielectric constant under low-frequency condition. At the same time, the CuO addition induces the piezoelectric properties to"hard". With the addition of CuO, both d33 and kp reduce, but Qm increases. |
