Temperature Dependent Piezoelectric and Pyroelectric Response of Nb Doped (Na0.41K0.09Bi0.5)TiO3 Ceramics

In the present study, temperature dependence of the piezoelectric and pyroelectric coefficients of niobium (Nb) doped (Na0.41K0.09Bi0.5)TiO3 [NKBT] ceramics has been investigated. The piezoelectric charge coefficient (d(31)) and electromechanical coupling coefficient (k(p)) increase gradually with temperature till close to the depolarization temperature and thereafter fall sharply. The highest piezoelectric coefficients were obtained for x = 0.005 (0.5 at.% Nb) which are d(33) similar to 185 pC/N, d(31) similar to 51 pC/N and k(p) similar to 0.35 at room temperature. Like the piezoelectric response, the pyroelectric coefficient also shows an anomaly in the vicinity of T-d. At room temperature the pyroelectric coefficient (p(3)) is in the range of 2-10 nC/cm(2)K for all the compositions. The maximum value of p(3) observed near T-d is 4.6 mu C/cm(2)K. The measurements reveal the lowering of T-d with increase in Nb content which can be explained on the basis of donor type behavior of niobium (Nb5+) ion. For energy harvesting, the generated output voltage shows maximum value for a periodic temperature oscillation of Delta T similar to 15 K at dT/dt similar to 0.44 K/s for sample with x = 0.005. The study suggests that by using a proper rectifier circuit a pulsating DC output with maximum voltage of similar to 3V can be obtained.