Stable pyroelectric coefficient induced from self-polarization in sol-gel derived 0.7Pb(Mg_1/3Nb_2/3) O₃-0.3PbTiO₃ thin films

Ferroelectric and pyroelectric properties of 0.7Pb(Mg_1/3Nb_2/3) O₃-0.3PbTiO₃ thin film deposited on Pt/Ti/SiO₂/Si substrates using a sol-gel method were investigated. X-ray diffraction results showed that the films were highly (111) oriented. It was found that the films show a stable pyroelectric coefficient (1.58 × 10^-8Ccm ^-2K^-1) without any poling processes. Nearly constant pyroelectric coefficient was obtained when the applied poling dc bias field increased to greater than three times of its coercive field. The pyroelectric coefficient of the poled 0.7Pb(Mg_1/3Nb_2/3) O₃-0.3PbTiO₃ thin film capacitor dropped to 96% of its initial value after ten days, which was much more stable than that of PZT samples. Asymmetric pyroelectric currents were found in the 0.7Pb(Mg_1/3Nb_2/3) O₃-0.3PbTiO₃ thin films with different poling directions. For positive poling, pyroelectric current increased with the poling electric field. In the case of negative poling, pyroelectric current decreased with the poling electric field. These results suggest that the good pyroelectric properties of the 0.7Pb(Mg_1/3Nb_2/3) O₃-0.3PbTiO₃ thin films could be due to the presence of self-polarization in this material.