An understanding of polarization-heat interactions in pyroelectric and electrocaloric thin-film materials requires that the electrothermal response is reliably characterized. While most work, particularly in electrocalorics, has relied on indirect measurement protocols, here we report a direct technique for measuring both pyroelectric and electrocaloric effects in epitaxial ferroelectric thin films. We demonstrate an electrothermal test platform where localized high-frequency (approximately 1 kHz) periodic heating and highly sensitive thin-film resistance thermometry allow the direct measurement of pyrocurrents (<10 pA) and electrocaloric temperature changes (<2 mK) using the "2-omega" and an adapted "3-omega" technique, respectively. Frequency-domain, phase-sensitive detection permits the extraction of the pyrocurrent from the total current, which is often convoluted by thermally-stimulated currents. The wide-frequency-range measurements employed in this study further show the effect of secondary contributions to pyroelectricity due to the mechanical constraints of the substrate. Similarly, measurement of the electrocaloric effect on the same device in the frequency domain (at approximately 100 kHz) allows for the decoupling of Joule heating from the electrocaloric effect. Using one-dimensional, analytical heat-transport models, the transient temperature profile of the heterostructure is characterized to extract pyroelectric and electrocaloric coefficients.
Bibliographical noteFunding Information:
S.P. acknowledges support from the Army Research Office under Grant No. W911NF-14-1-0104. A.R.D. acknowledges support from the National Science Foundation under Grant No. CMMI-1434147. A.D. acknowledges support from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award No.DE-SC-0012375. L.W.M. acknowledges support from the National Science Foundation under Grant No. DMR-1451219. C.M. acknowledges funding from the Swiss National Science Foundation under Grant No. P2ELP2-152177.
© 2017 American Physical Society.