Spontaneous polarization and pyroelectric coefficient of lithium niobate and lithium tantalate determined from crystal structure data
Tina Weigel, Christian Ludt, Tilmann Leisegang, Erik Mehner, Sven Jachalke, Hartmut Stöcker, Thomas Doert, Dirk C. Meyer, Matthias Zschornak
Abstract
This work shows an alternative approach to extract the pyroelectric coefficient directly from the response of the crystal structure to temperature variations. The approach uses crystal structure parameters determined at different temperatures and Born effective charges calculated by density functional theory to evaluate the spontaneous polarization. On this basis, the pyroelectric coefficient is calculated using the first derivative of the polarization with respect to temperature. In this work, we utilize laboratory single-crystal x-ray diffraction in a temperature range from 80 to 400 $\mathrm{K}$ to demonstrate this approach on the standard pyroelectric materials lithium niobate and lithium tantalate. The accuracy of the presented method for the spontaneous polarization is on par with reported experimental data and relative errors are below $7\phantom{\rule{0.16em}{0ex}}%$. Our determined pyroelectric coefficients have larger errors, but are within the range of reported literature values. The outlined semitheoretical method is recommended when electrical characterization under temperature change is not feasible, e.g., when the preparation of large area contacts is problematic or only small sample volumes are available ($<100$ $\phantom{\rule{0.16em}{0ex}}\textmu{}{\mathrm{m}}^{3}$).