Secondary pyroelectric and electrocaloric effects in thin films

Pyroelectric;electrocaloric;secondary effect;laser-based methods;thermal conductivity;sol-gel;thin films;Heat Transport

Tong, Trong Van

关键词: Pyroelectric;    electrocaloric;    secondary effect;    laser-based methods;    thermal conductivity;    sol-gel;    thin films;    Heat Transport;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/87957/TONG-DISSERTATION-2015.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The pyroelectric and electrocaloric effect play an important role in many applications such as energy harvesting and solid-state cooling. This dissertation focuses on the characterization of the pyroelectric and electric coefficient in thin film using novel laser-based technique. The implementation of the systems is described in detail, and heat transport models are developed to interpret the experimental data. The temperature oscillation caused by the modulated laser power or the entropy change are calculated over a wide range of the modulation frequency. These techniques are applied to characterize Pb(ZrTi)O3 and Ba(SrTi)O3 films growth by Pulse Laser Deposition (PLD) and sol-gel method.The secondary pyroelectric and electrocaloric contributions caused by clamping substrate effect are discussed. A wide range frequency analysis is applied to extract the secondary pyroelectric coefficient.The secondary pyroelectric effect is found to have the same dependence on applied field as the pyroelectric coefficient and is approximately 15% and 20% of the total response for PbZr0.2Ti0.8O3 and Ba0.6Sr0.4TiO3 grown by PLD, respectively. By comparing the pyroelectric and electrocaloric coefficient measured on the same devices, our result shows the secondary contribution to the electrocaloric coefficient has the opposite sign as the primary effect and therefore reduces the overall entropy change of Pb(ZrTi)O3 in an electric field. Finally, the sol-gel method is used to produce Pb(ZrTi)O3 thin films. The sample fabrication is described in detail along with physical characterization and the pyroelectric measurement. Sol-gel PZT films are perovskite phase with (100) orientation. The pyroelectric coefficient is measured to be 135 µC m-2 K-1.