Phase transitions in Na1-xLixNbO3 solid solution ceramics studied by a new pyroelectric current based method

The pyroelectric current response is one of the most important features of ferro-piezoelectric materials. The polarization versus temperature curve is the main signature of the phase transitions in these materials. The integration of the thermally stimulated current (TSC) released by polarized samples on increasing T has been used to reproduce the polarization versus temperature behaviour. However, in the TSC current there are contributions coming from sample conductivity, released charges and ferroelectric relaxation, among others, that become more important for high T-c ferroelectrics. In this work a new approach of analysis of the TSC current is proposed to extract the 'true' pyroelectric current arising from the fluctuations of the temperature gradient applied to the sample. This new analysis is first tested with a well-known PZT ceramic and then applied to the study of phase stability and transitions in lead-free ferro-piezoelectric (Na1-xLix) NbO3 solid solution ceramics with 0 < x <= 0.12. Special emphasis is laid on the ferroelectric phase stabilization for the x = 0.5 sample.