INTRODUCTONThe development of telecommunication systems based on the application of acoustic waves in informa tion transmission and processing under real time condi tions demands new promising piezoelectric materials with a high electromechanical coupling coefficient and good temperature properties. Recently, significant attention has been paid to crystals of the lanthanum gallium silicate group; these crystals have unique acous tic properties (some crystal cuts have zero temperature coefficients at relatively high electromechanical cou pling coefficients). Over the last few years, we have per formed studies of langasite La 3 Ga 5 SiO 14 and langatate La 3 Ga 5.5 Ta 0.5 O 14 crystals, which are now becoming basic materials for acoustoelectronics [1][2][3][4].In the present work a new piezoelectric material of the lanthanum gallium silicate group (the five com ponent crystal Ca 3 TaGa 3 Si 2 O 14 (CTGS)) has been grown using the Czochralski method and studied. The structural and acoustic properties of the CTGS crystal were studied by means of the X ray diffraction method. Figure 1 presents the CTGS crystal grown along the crystallographic axis [01.0] from a melt using the Czochralski method at a temperature of 1350°С. The crystal pulling speed was about 2 mm/h at a crystal rotation speed of 10 rpm. After growth, the crystals underwent high temperature annealing in air at 1100°С for 2 days. The crystal weight was 460 g with a diameter of the cylindrical part of 38-41 mm and a total length of 100 mm. The crystal had a homoge neous light pink color and was transparent over the entire bulk. Cracks, scattering centers and other visi ble defects were not observed.
SYNTHESIS OF THE Ca 3 TaGa 3 Si 2 O 14 (CGTS) CRYSTAL AND STUDIES OF ITS STRUCTURETo determine the unit cell parameters, the X ray phase analysis method was used. Figure 2 shows a dif fractogram for the CTGS crystal. Based on measure ments of the positions of Bragg peaks for the respective reflections and the Bragg lawwhere d is the interplane distance, θ B is the Bragg angle for the corresponding planes, λ is the the X ray radia tion wavelength, one can easily determine the unit cell parameters. Since the CTGS crystal has the space symmetry group 32 and a hexagonal unit cell, its parameters are as follows: a = 2 = 8.14860 Å, c = 4.98822 Å. B 2 sin , d n θ = λ (110) Abstract-A new promising piezoelectric material Ca 3 TaGa 3 Si 2 O 14 (CTGS) has been grown using the Czo chralski method. Its unit cell parameters have been determined by means of the X ray phase analysis method. The X ray diffractometry method was used to study the crystal acoustic properties; the velocities of surface acoustic wave propagation were measured for the first time and the power flow angles were determined.
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