| High temperature piezoelectric crystals are widely used in many fields, such as aerospace field, oil exploration and automobile industry. This paper mainly focuses on the growth and quality of high temperature piezoelectric crystals Yx Gd1-x Ca4O(BO3)3(abbreviated Yx Gd1-x COB). High temperature piezoelectric crystal Yx Gd1-x COB was grown successfully, and the dielectric properties, piezoelectric properties and thermal expansion of this crystal were studied. The main contents and results are as follows:(1)The polycrystalline Yx Gd1-x Ca4O(BO3)3 compounds were synthesized by solid phase method. Calculated from X-ray powder diffraction, the lattice parameters of YCa4O(BO3)3(abbreviated YCOB) were a=8.07?, b=16.01?, c=3.524? and ?=101.16°. Yx Gd1-x Ca4O(BO3)3 crystals were grown by the Czochralski pulling technique using PERI-400 P single crystal furnace produced by Xi an bai rui technology development company. The crystal quality was characterized by using D8 Advance X-ray diffraction instrument(Cu, ?=0.15406 nm) and testing range was 2?=0-70 o, scanning speed was 1o/min, contrasted it to the PDF standard card of YCOB crystal, the position and strength of peaks are unanimous. It indicates that the structure of Yx Gd1-x COB crystal is similar to the structure of YCOB crystal and Gd COB crystal. The lattice parameters were a=8.088?, b=16.006?, c=3.548? and ?=101.34 o, contracted to the lattice parameters of YCOB crystal(a=8.077?, b=16.02?, c=3.534? and ?=101.19o) and the lattice parameters of Gd Ca4O(BO3)3(abbreviated Yx Gd1-x COB) crystal(a=8.104?, b=16.03?, c=3.558? and ?=101.25o).(2)The relative dielectric constants along x-axis, y-axis and z-axis of Y0.145Gd0.855 COB crystal were measured by bridge measurement, the frequency of electric field was 10 KHz, the voltage was 1V, the temperature range was 30 ?-600 ? and temperature rise rate was 5 ?/min. The relation between temperature and dielectric was discussed. The relative dielectric constants of Y0.145Gd0.855 COB crystal was compared to the relative dielectric constants of YCOB crystal and Gd COB crystal. The relative constants of Y0.145Gd0.855 COB crystal is greater, the dielectric properties of Y0.145Gd0.855 COB crystal is greater. The dielectric loss coefficients of Y0.145Gd0.855 COB crystal were tan?11=0.034%,tan?22=0.046%,tan?33=0.03% at 30?. The dielectric loss coefficients of Y0.145Gd0.855 COB crystal has small value.(3)The sample for testing piezoelectric coefficients d26 was ZX-cut. Piezoelectric coefficient d26 of Y0.145Gd0.855 COB crystals was 9 p C/N at room temperature. It can be found that the piezoelectric coefficient d26 of Y0.145Gd0.855 COB crystal is larger than that of YCOB crystal but less than that of Gd COB. It is believed that the radius of Re ions and the disorder distribution of Re3+ and Ca2+ ions contribute to the piezoelectric coefficient d26 of Re COB crystals.(4)There are four independent thermal expansion coefficients(?11, ?22, ?33, ?13) for Y0.145Gd0.855 COB crystal. And the ?13 can be negligible because of smaller value. The thermal expansion coefficients of Y0.145Gd0.855 COB crystal were measured, Temperature range was 20-600 ? and heating speed was 30 ? per hour. The thermal expansion coefficient was determined to be ?11=12.97, ?22=5.94, ?33=8.03(10-6/?) for Y0.145Gd0.855 COB crystal. The thermal expansion coefficient of Y0.145Gd0.855 COB crystal was compared to the relative dielectric constants of YCOB crystal and Gd COB crystal. The anisotropy of Y0.145Gd0.855 COB crystal is more obviously, so we should pay attention to temperature field control when grown crystal and using the crystal. |
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