The effect of the addition of Bi-perovskites to (Li 0.04 K 0.52 Na 0.44 )(Nb 0.84 Ta 0.1 Sb 0.06 )O 3 (LF4) ceramics was studied to improve the properties of lead-free piezoelectrics. Ceramics with the relative density above 96% were successfully obtained by a solid state reaction process. The changes in lattice parameters indicated that the vacancy concentration at the A-site of the perovskite structure and the tetragonality of the crystal lattice were reduced with the addition of BiFeO 3 . The addition of BiFeO 3 changed the LF4 to a soft-piezoelectric.··The electrical insulation of the LF4 was improved with the addition of BiFeO 3 , which made a full poling possible under high electric fields. A few mol% of BiFeO 3 was effective to improve the remanent polarization of the LF4 ceramics and a piezoelectric d 33 constant of about 358 pm/V was obtained in the 0.4 mol% doped ceramics.
Three kinds of sintering aids, LiBiO2, CuBi2O4 and LiBO2, were selected as sintering aids for the low temperature sintering of (Li0.04K0.52Na0.44)(Nb0.84Ta0.1Sb0.06)O3 (LF4) ceramics and the effects of these compounds on the sintering behavior of the LF4 ceramics was investigated. The addition of LiBiO2 decreased the sintering temperature of LF4 about 100°C but the effect was limited and the broadening of XRD peaks due to the degradation of crystallinity was observed. The CuBi2O4 was also effective to decrease the sintering temperature of LF4 ceramics but a secondary phase was formed when a large amount of CuBi2O4 was added. The addition of a small amount of LiBO2 was very effective to decrease the sintering temperature of LF4 ceramics. By optimizing the sintering conditions, ceramics with the relative density of 95% were obtained at 950°C which was lower than the melting point of Ag. Li ions in LiBO2 were incorporated into the LF4 lattices, giving rise to the degradation of piezoelectric properties through the change of crystalline phase. The addition of excess Na with LiBO2 restricted the incorporation of Li ions into the lattice. Ceramics sintered at 950°C showed the relative permittivity of 738 and the d33 constant of 138 pC/N at room temperature.
Bi-perovskites, such as BiFeO3 (BF), BiInO3 (BI) and BiScO3 (BS), were added to (Li0.04K0.52Na0.44)(Nb0.84Ta0.1Sb0.06)O3 (LF4) to improve the piezoelectric properties of lead-free piezoelectric ceramics. The addition of Bi-perovskites up to 0.6 mol% did not depress the sinterbility of ceramics and the relative densities above 96% could be achieved by a powders-solid state reaction process. The c/a ratio of the tetragonal lattice of the LF4 ceramics was monotonously reduced with the amount of the BF added. The electrical insulation of the LF4 was improved with the addition BF, making the poling procedure under high electric fields become easy. The addition of BF was also effective to enhance the remnant polarization of the LF4 and the piezoelectric d33 constant of 358 pm/V was obtained by the addition of 0.4 mol% BiFeO3. However, the enhancement of the remnant polarization was not observed when the BI and BS were added to the LF4.
