Temperature Dependence of Permittivity and Loss Tangent of Lithium Tantalate at Microwave Frequencies M. V. Jacob a , J. G. Hartnett b , J. Mazierska a , V. Giordano c , J. Krupka d , and M. E. Tobar b a Electrical and Computer Engineering, James Cook University, Townsville, Q4811, Australia, b School of Physics, University of Western Australia, Perth, WA, Australia, c LPMO CNRS, 32 av. de l’Observatoire, F-25044 Besançon, France, d Instytut Mikroelektroniki i Optoelektroniki Politechniki Warszawskiej, Koszykowa 75, 00-662 Warszawa, Poland. ABSTRACT Lithium Tantalate 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 LiTaO 3 crystals in the temperature range from 14 K to 295 K at a frequency of 11.4 GHz and 10 GHz. Microwave properties of LiTaO 3 were determined by measurements of the resonance frequency and the unloaded Q o -factor of a TE 011 mode cylindrical cavity containing the sample under test and accounting for uncalibrated cables and adaptors inside the cryocooler. The permittivity of LiTaO 3 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 Lithium Tantalate is suitable for microwave applications. Key Words: LiTaO 3 , Tantalates, Dielectric materials, Microwave properties 1. INTRODUCTION Lithium Tantalate (LiTaO 3 ) single crystals possess a combination of unique electro-optic, acoustic, piezoelectric, pyroelectric and non-linear optical properties [1]. They are commercially used in integrated optics as modulators, in pyroelectric detectors and in surface acoustic wave (SAW) devices; TV modulators, video games and wireless alarms, and cordless phones, pagers, wireless handsets and microwave relay link devices. Currently Lithium Tantalate and a similar material, Lithium Niobate, are under consideration for novel nonlinear optical applications such as second harmonic generation and optical parametric oscillations [2]. Lithium Tantalate single crystals are typically produced by the Czochralski method because this is the most effective technique to reduce composition variation [3]. The variation of Li to Ta concentration, as high as 8%, influences all parameters of the material. Basic parameters of LiTaO 3 single crystals are given in Table 1 together with parameters of Lithium Niobate (LiNbO 3 ) for the comparison [1, 4]. LiTaO 3 exhibits a smaller thermal expansion coefficient than LiNbO 3 and is easier to machine. Also it has a higher damage threshold; above 500 MW/cm 2 for nanosecond pulses [5]. Even though Lithium tantalate single crystals have been reported to be used in microwave applications very few data on microwave properties on this dielectric are available. Results of a conducted search on values of the complex permittivity of LiTaO 3 are shown in Table II. 1