Temperature dependent energy storage behaviour of relaxor-ferroelectric epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 thin film capacitors
The influence of temperature on the energy storage behavior of relaxor-ferroelectric epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) thin film capacitors fabricated using pulsed laser deposition was evaluated using cyclic I-V measurements from 25 °C to 225 °C in order to elucidate ferroelectric and dielectric contributions across the Curie temperature. In the film thickness range of 125 nm to 500 nm, it has been found that the leakage current through the capacitors increases monotonically with increasing temperature and the effect is more prominent at smaller film thickness, primarily due to a more efficient movement of ferroelectric domains. While these effects prevent thinner PLZT films from maintaining adequate energy storage efficiencies at temperatures above~ 100 °C, thicker films show promising energy storage properties in a wide temperature range. Specifically, the 500 nm thick PLZT film capacitors have a nearly constant energy storage efficiency above ~70% in the temperature range of 25 °C to 175 °C, with a peak efficiency of 78% at 175 °C due to the large dielectric constant exceeding ~2000 as the temperature approaches the PLZT Curie temperature of 200 °C. By quantifying the three contributions of the electric conductivity, dielectric capacitance, and relaxor-ferroelectric domain switching polarization to temperature dependent energy storage properties of relaxor-ferroelectric capacitors, this study reveals that the dielectric contribution dominates in the PLZT capacitors with smaller thickness, while even contributions from all three components are present in films of larger thickness. These results suggest that the PLZT relaxor-ferroelectric thin film capacitors are promising for energy storage applications and further improvement of performance may be achieved by optimization of the film/electrode interface.