Effects of lanthanum doping on the grain size and piezoelectric properties of lead titanate ceramics

Modified lead titanate ceramics were prepared using mixed oxide route. A fixed amount of (1 mol%) iron (Fe) was added to get highly dense ceramics. Addition of 1 mol% tungsten (W) greatly enhanced the grain size. Lanthanum (La) concentration was changed from 2 to 25 mol%, keeping the concentration of Fe and W fixed at 1 mol%. The Curie temperature and tetragonality decreased with increasing La content. The dielectric constant showed a systematic increase with increasing La content. The piezoelectric coefficient were determined and it was found that the thickness coupling coefficient (k/sub t/) showed a marked increase with increasing La content reaching a peak value of 0.60 around 15 mol% while planar coupling coefficient (k/sub p/) was found to be almost independent of composition and having a value around 0.1. The hydrostatic figure of merit of about 1400 was achieved for 15 mol% of La which is one of the highest reported values even for hot pressed ceramics.