The paper presents an accurate evaluation of the temperature derivatives of elastic stiffness of lithium tantalate on SAW delay-temperature dependence data. We use nonlinear formalism to correct description of SAW propagation on X, Y-cuts of lithium tantalate plates subjected to homogeneous thermally-induced deformation. Least squares method is used to fit the temperature derivatives of the elastic constants of lithium tantalate to the measured SAW temperature coefficients of delay of the first (TCD1) and second (TCD2) orders. For sufficient decrease of computation time, the perturbation procedure is employed. That allows us to fit optimally the constants of crystals in order to get coincidence with experimental SAW delay-temperature data using only one iteration step in a computer. To measure the SAW temperature coefficients of delay we used a new highly sensitive method. The measurement errors of TCD1 and TCD2 are better than 0.15% and 5%, respectively. The sensitivity of the method is about 0.01%.
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