Temperature dependence of permittivity and loss tangent of lithium tantalate at microwave frequencies

Lithium tantalate (LiTaO₃) exhibits excellent electro-optical, piezoelectric, and pyroelectric properties and a very low thermal expansion. In this paper, we report measurements of loss tangent and the real part of the relative permittivity ε_r⊥ measured in c-axis LiTaO₃ crystals in the temperature range from 14 K to 295 K at a frequency of 11.4 and 10 GHz. Microwave properties of LiTaO₃ were determined by measurements of the resonance frequency and the unloaded Q_o factor of a TE₀₁₁ mode cylindrical cavity containing the sample under test and accounting for uncalibrated cables and adaptors inside the cryocooler. The permittivity of LiTaO₃ was found to increase from 38.9 to 41.1 and the loss tangent to change from 1.1×10^-4 to 6.5×10^-4 over the full temperature range. Due to its low loss and relatively high permittivity, LiTaO₃ is suitable for microwave applications.