Jiyeob Kim1,Djamila Lou1,Abel Fernandez1,Lane Martin1
University of California, Berkeley1
Jiyeob Kim1,Djamila Lou1,Abel Fernandez1,Lane Martin1
University of California, Berkeley1
There is a new demand for the next generation cooling system with the limited use of fluorinated gases that are widely used as coolants in the conventional cooling system that contributes to global warming. There is a growing interest in caloric studies based on solid-state phase transitions that can meet the new demand for cooling in compact spaces such as integrated circuits and batteries. Electrocaloric materials are considered relatively easy to drive with an electric field. They are often studied in thin-film form to achieve a large breakdown field. Thin films have a small thermal mass that limits from direct measurement and many studies use indirect method to report electrocaloric effects. However, this could lead to erroneous values due to substrate clamping and heat dissipation to the substrate.<br/><br/>In this work, we explore indirect and direct methods to study the electrocaloric effect in relaxor ferroelectric 0.68PbMg<sub>1/3</sub>Nb<sub>2/3</sub>O<sub>3</sub>-0.32PbTiO<sub>3</sub> (PMN-32PT) thin films. PMN-32PT is known to have an extremely high electromechanical coupling, especially with compositions near morphotropic phase boundary (MPB). Ba<sub>0.5</sub>Sr<sub>0.5</sub>RuO<sub>3</sub> (30 nm) ∥ PMN-32PT (150 nm) ∥ Ba<sub>0.5</sub>Sr<sub>0.5</sub>RuO<sub>3</sub> (30 nm) heterostructures were grown on NdScO<sub>3</sub> (110) substrates via pulsed-laser deposition providing -0.5% strain on PMN-32PT. Subsequently, a 6-terminal electrothermal testing platform, adapted from a 3-omega device configuration, was fabricated via photolithography. This device allows us to apply an electric field to PMN-32PT and measure polarization and temperature change to study electrocaloric effect using both indirect and direct methods, respectively. Furthermore, we have successfully prepared freestanding versions of these same heterostructure and fabricated them into the testing platform to explore how the removal of the substrate constraints (clamping) impacts the evolution of these properties. This study should clarify the elements that contribute to discrepancies in indirect and direct electrocaloric studies in thin films and provide a guide for indirect studies for accurate calculations.