Moving Curie Temperature Of BZT-BCT Lead-Free Piezoelectric Ceramics

Lead-free piezoelectric ceramics Ba(Ti0.8Zr0.2)O3-(Ba0.7Ca0.3)TiO3(BZT-BCT) system exhibits excellent piezoelectric properties at room temperature, and is considered as the most likely alternative material to lead-based piezoelectric ceramics. But the key drawback of BZT-BCT materials lies in its relatively low Curie temperature(<93 °C), and the Sndoped in BZT-BCT ceramic even lower than 85 oC. This limits its practical application. This paper used conventional solid-state reaction process prepared BZT-BCT based leadfree piezoelectric ceramics. Study on two mechanisms for moving the Curie temperature: Ba(Cu1/2W1/2)O3 doping for its high Curie temperature to BZT-BCT, and another is substituting Zr by Ge that is manily attributed to the Zr in BZT decreased the TC of BZT ceramics.The study found that the system would get the best piezoelectric constant(d33 = 453pC/N) and electromechanical coupling factor(kp = 48%) when BZST-BCT doped with 0.2 mol% BCW. The dielectric ?r was improved compared with no BCW doping. Curie temperature enhanced from 82.5 oC to 87.5 oC with doping 0.2mol% BCW. With more BCW was doped, the Curie temperature changed little, and the piezoelectric performance decreased gradually.The addition of Ge could raise TC of 50Ba(Ti0.8Zr0.2-xGex)O3-50(Ba0.7 Ca0.3)TiO3(BZGxT-BCT, x = 0-0.16) ceramics from 93 °C at x = 0 to 127.5 °C at x =0.16 with a relatively high d33 of no less than 103 pC/N. BZGxT-BCT ceramics sintered at 1350 °C for 4 h exhibited the highest d33 = 510 pC/N at x = 0.02 with TC = 99.8 °C. With the increasing content of Ge(i.e. x), the TC shifted toward high temperature, while the TT-R toward low temperature. These results indicated that BZGxT-BCT ceramics are promising for practical applications as lead-free piezoelectric materials. Studies have shown that the formation of second phase doesn't contribute to the Curie temperature of the system, and impair the electrical properties of the system.