Piezoelectric properties of bismuth modified lead titanate ceramics

Effect of Bi additives on the piezoelectric properties of PT ceramics having the formula (Pb_1-3x/2Bi_x)(Ti_0.98Mn_0.02)O ₃ with x=0.04, 0.06, 0.08 was investigated. The samples were prepared by conventional ceramic technique, using p.a. purity raw materials. The mixed powders were sintered at temperatures between 1050-1300degC. Poling was done in fields of about 70 kV/cm. Density and coupling factors of the samples were determined as a function of sintering temperatures, and doping level. Temperature dependence of the main piezoelectric characteristics was also investigated for temperatures as high as 500degC. A Curie point of 450degC, a low dielectric constant (<140) and a large electromechanical anisotropy (the radial mode is nearly inexistent, at room temperature and the thickness coupling factor is about 0.4) were found. These enhanced properties make such ceramics very attractive for high temperature and high frequency transducers applications