Determination of Nonlinear Dielectric and Electrostrictive Constants of Lithium Tantalate Single Crystal

To increase telecommunications capacity, surface acoustic wave (SAW) devices have become smaller and have more channels and higher power. However, the intermodulation caused by material nonlinearity has become increasingly apparent. To effectively utilize SAW devices in sixth-generation communication systems, it is necessary to mitigate this nonlinearity.<br/>However, a full set of nonlinear constants (nonlinear elastic, piezoelectric, electrostrictive, and dielectric constants) for piezoelectric single crystals has been measured for only lithium niobate (LiNbO₃) single crystals[1]. The nonlinearity of a single crystal of lithium tantalate (LiTaO₃), the most widely used ferroelectric crystal in SAW devices for communications, has not been quantitatively evaluated.<br/>Against this background, we started research on the measurement of all nonlinear constants of LiTaO₃ single crystals as part of basic research for the realization of next-generation ultra-low-nonlinearity SAW devices.<br/>This paper describes a measurement methods and reports the obtained nonlinear dielectric constants and electrostrictive constants for LiTaO₃. In the experiment, a dynamic measurement method based on capacitance variation with an alternating electric field was employed for the nonlinear dielectric constants [2] and capacitance variation under applied stress was also measured for electrostrictive constants.<br/>We show the measured relative capacitance variation in LiTaO₃ single crystal plate as a functions of an applied electric field and stress, respectively. Using measured five data (for nonlinear dielectric constants) and twenty data (for electrostrictive constants) with different crystal orientation, we have determined three independent nonlinear dielectric constants and eight electrostrictive constants in the stress-free state (d-form) ε^T_ijk and ²d_(ij)k. The corresponding nonlinear constants in the strain-free state (e-form) ε^S_ijk and ²e_(ij)k were also calculated using the d-from constants and will be presented at the meeting.<br/><br/>References:<br/>[1] Y.Cho and K.Yamanouchi:"Nonlinear,Elastic, Piezoelectric, Electrostrictive, and Dielectric Constants of Lithium Niobate ", J. Appl. Phys.,Vol.61 (1987) pp.875-887.<br/>[2] Y.Cho and F.Matsuno:"Dynamic Measuring Method of Capacitance Variation of Piezoelectric Ceramics with Alternating Electric Field", Jpn. J. Appl. Phys., Vol.31 (1992) pp.3627-3631.