Depolarization of ferroelectrics measured by their piezoelectric and elastic response

Along with current efforts to replace toxic lead-based materials, the increasing demand for piezo-devices has led to intensive research to find new materials that are environmentally friendly and suitable for future applications [1, 2]. These applications require knowledge about the thermal evolution of the piezoelectric coefficient (usually d33) as well as the depolarization temperature (Td), which often determines the upper temperature limit for their operation [1, 2]. However, Td of ferroelectrics is often determined by dielectric constant measurements, which provide no information on the thermal evolution of the piezoelectric coefficient. In this talk, Resonant Piezoelectric Spectroscopy (RPS) [3, 4] is demonstrated to be a convenient and complementary method to measure the temperature dependence of the piezoelectric coefficient d33 with reasonable accuracy and determine Td through piezoelectric and elastic anomalies with examples on BaTiO3 and PbSc0.5Ta0.5TaO3. Then, it is applied to lead-free piezoelectric Na0.5Bi0.5+xTiO3+0.15x (x = -0.02, -0.01, 0, 001, 0.015) to investigate the role of Bi-nonstoichiometry on the depolarization temperature in Na0.5Bi0.5TiO3. The sample with minimal concentration of defects (x = 0.01) had a Td depressed by 40°C with respect to other samples. This indicates the role of defects in domain wall pinning in increased Td. Results are particularly important for applications of NBT-based materials, which require tuning of Td depending on whether probed applications are based on piezoelectricity (below Td) or large strains needed in actuators (above Td). [1] A. J. Bell, T. P. Comyn, T. J. Stevenson, Expanding the application space for piezoelectric materials, APL Mater. 9 (2021) 010901. [2] T. Zheng, J. G. Wu, D. Q. Xiao, J. G. Zhu, Recent development in lead-free perovskite piezoelectric bulk materials, Prog. Mater. Sci. 98 (2018) 552-624. [3] O. Aktas , M. Kangama, G. Linyu, G. Catalan , X. Ding, A. Zunger, E. K. H. Salje, Piezoelectricity in nominally centrosymmetric phases, Phys. Rev. Res. 3 (2021) 043221. [4] O. Aktas, M. Kangama, G. Linyu, X. Ding, M. A. Carpenter, E. K. H. Salje, Probing the dynamic response of ferroelectric and ferroelastic materials by simultaneous detection of elastic and piezoelectric properties, J. Alloys and Compounds 903 (2022) 163857.