Effect of Ta-Substitution on the Ferroelectric and Piezoelectric Properties of Bi0.5 (Na0.82K0.18)0.5TiO3 Ceramics

The effect of Ta substitution on the crystal structure, ferroelectric, and piezoelectric properties of Bi-0.5(Na0.82K0.18)(0.5)Ti(1-x)TaxO(3) ceramics has been investigated. The Ta doping resulted in a transition from coexistence of ferroelectric tetragonal and rhombohedral phases to an electrostrictive pseudocubic phase, leading to degradations of the remnant polarization, coercive field, and piezoelectric coefficient d(33). However, the electricfield- induced strain was significantly enhanced by the Ta substitution-induced phase transition and reached a highest value of S-max/E-max = 566 pm/V under an applied electric field 6 kV/mm when 2% Ta was substituted on Ti sites. The abnormal enhancement in strain was attributed to the pseudocubic phase with high electrostrictive constants.