Comparison of piezoelectricity in Ta 5+ and La 3+ substituted lead calcium titanate ceramics

Abstract

This paper reports the experimental investigations on the effect of La 3+ and Ta 5+ 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 Pb 0.76− x /2La x Ca 0.24(Ti 0.98Mn 0.02) 1− x /2O 3 and Pb 0.76Ca 0.24Mn 0.02Ti 0.98−5 x /4Ta x O 3, 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 ( d 33, d 31) increased with La 3+ substitution due to reorientation of the grains and decreased with Ta 5+ substitution because of the increase in porosity. Figure of merit d h g h 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.