Modified Lead Calcium Titanate Ceramics with a Relatively Large Dielectric-Constant for Hydrophone Applications

Modified lead titanate of the base composition (Pb,Ca)Ti-(Co,W)O3 + 0.01 mol % MnO was doped with 2 to 6 mol % strontium and barium to increase the dielectric constant, K, while preserving a high piezoelectric anisotropy (d33/d31). K was increased above 500 and a d33/d31 ratio of 34/1 was achieved when the composition Pb0.65Ca0.31Sr0.04Ti0.94-(Co0.5W0.5)0.06O3 + 0.01 mol% MnO was fabricated. The large d33/d31 resulted in an impressive hydrostatic piezoelectric coefficient (d(h) = 81 X 10(-12) m2/V). The relatively low transition temperature (T(c) = 120-degrees-C) did not result in an increased aging rate when samples were tested at 40-degrees-C and 99% humidity for 120 h after poling. A small tetragonality ratio (1.008) enabled saturation of ceramic properties at poling fields as low as 30 kV/cm at 100-degrees-C.