Comparison of piezoelectricity in Ta5+ and La3+ substituted lead calcium titanate ceramics

This paper reports the experimental investigations on the effect of La3+ and Ta5+ substitution on the structural characteristics and dielectric and piezoelectric properties of lead calcium titanate (PCT) ceramic. The PCT samples with A-site and B-site substitution having the composition formula Pb0.76−x/2LaxCa0.24(Ti0.98Mn0.02)1−x/2O3 and Pb0.76Ca0.24Mn0.02Ti 0.98−5x/4TaxO3, x=0 and 0.02, respectively, were prepared using conventional solid-state reaction method. Phase formation and structural analysis were studied using X-ray diffraction and scanning electron microscopy, respectively. Dielectric constant (ε′) and loss tangent (tan δ) as a function of frequency were measured at room temperature as well as elevated temperature. Both ε′ and tan δ decreased with increase in frequency at room temperature. Curie temperature decreased with La and Ta doping in PCT ceramics due to a decrease in the tetragonality of PCT ceramics. Piezoelectric charge coefficients (d33, d31) increased with La3+ substitution due to reorientation of the grains and decreased with Ta5+ substitution because of the increase in porosity. Figure of merit dhgh increased and decreased with La and Ta substitution, respectively. A good ferroelectric behaviour is obtained for La substitution, while no hysteresis is obtained for Ta substitution.