DEVELOPMENT OF NEW PIEZOELECTRIC CERAMICS

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New piezoelectric ceramics based on bismuth nickel titanate are developed. Ferroelectric and piezoelectric properties of a new solid solution, [Bi_<1-x> (Pb_<1-y>Bay)_x] [Ni_<(1-x)/2>Ti_<(1+x)/2>] O_3, are studied in detail. Ceramic samples are prepared according to the conventional seramic sintering technique.The crystal phase of the solid solution is a perovskite structure with x<greater than or equal>0.3. On the other hand, the phase with x<0.3 belongs to a bismuth layr structure. The (Bi_<1-x>Pb_x) (Ni_<(1-x)/2>Ti_<(1+x)/2>) O_3 (y=0) (BPNT-100x) has a morphotropic phase boundary between a rhombohedoral phase and a tetragonal phase at x=0.445. The Curie temperature, Tc, depends on the amount of Pb and/or Ba ions. For example, the Tc is over 400ﾟC in BPNT-50 (x=0.5 and y=0). D-E hysteresis loops are observed to obtain the remanent polarization, Pr and the coercive field, Ec.To improve the low breakdown voltage for poling due to the low resistivity, manganese doping is more effective. The resistivity, rho, of 0.02 wt%-Mn-doped ceramics is 10^<12>-10^<13> OMEGA・cm at room temperature while the rho without Mn doping is 10^8-10^9 OMEGA・cm. The electromechanical coupling factors, kt, kp, k33 and k31 in the thickness, the planar, longitudinal and transverse modes of the BPNT-50 are 0.438,0.287,0.509 and 0.237, respectively. These values are almost the same as those of the PbTiO3-based high-Tc piezoelectric ceramics. However, these values are slightly lower than the values expected from their large Pr. The relationship between piezoelectric and mechanical properties should be investigated on the solid solution.