Single crystals of ferroelectric lithium niobate–tantalate LiNb_1–xTa_xO₃ solid solutions for high-temperature sensor and actuator applications

Ferroelectric LiNb_1–xTa_xO₃ solid solutions with various Nb/Ta ratio were grown from the melt by the Czochralski method. The exact composition of the grown crystals was determined by inductively coupled plasma atomic mass spectrometry. The dependence of the crystal composition on the composition of the initial melt was obtained and explained by a wide separation between the phase boundaries of the liquid and solid phases on the LiNbO₃–LiTaO₃ phase diagram. Using high-resolution X-ray diffraction, the parameters a and c of a crystal unit cell were determined (LiNb_0.88Ta_0.12O₃: a = 5.1574 Å and c = 13.8498 Å). Further, the Curie temperature T_C of the crystals was measured using the differential scanning calorimetry technique. T_C was found to depend on the composition of the crystals that allowed conditions for the monodomainization of the grown crystals to be defined (LiNb_0.88Ta_0.12O₃: T_C = 1102°C; LiNb_0.33Ta_0.67O₃: T_C = 794°C). Finally, the velocity of surface acoustic waves was determined by scanning electron microscopy and X-ray diffraction techniques (YZ-cut of a LiNb_0.88Ta_0.12O₃ crystal: V = 3440 m s⁻¹).