Temperature coefficients of selected material constants of dilithium tetraborate (Li2B4O7)

Dilithium tetraborate is a promising piezoelectric material for both bulk acoustic wave and surface acoustic wave devices. In order to design temperature compensated devices, it is necessary to know the behavior of the material constants with respect to temperature variations. In this paper, the first and second order temperature coefficients of the material constants c₁₁^E, c₁₂^E, c₆₆^E, and e₁₅ of Li₂B₄O₇ have been measured over a temperature range of 20°C to 150°C. An improved resonator method was used to measure the fundamental zero mass loading antiresonance frequencies of selected pure-mode orientations of Li₂ B₄O₇. Material constants extraction was performed using a linear least squares matrix method. The resulting material constant curves were fit with a third order power series to obtain their corresponding temperature coefficients. The calculated first order temperature coefficients of the material constants show reasonable agreement with previously published values. The calculated second order coefficients do not agree well with the previously published values, and may help to resolve the large discrepancies between predicted and measured behavior of Li₂B₄O ₇ resonators