We present a relationship between piezoelectric property and crystal structure in melilite-type crystals. Two independent piezoelectric constants, d 14 and d 36 , increase and decrease with the polyhedral distortion, respectively. Based on this knowledge, single crystals made of strontium-substituted calcium magnesium silicate Ca 2 MgSi 2 O 7 (CMS) have been submitted to the Czochralski method, which made them grown. The CMS crystal has a high d 36 ; however, its transition temperature is around 85°C. Therefore, the strontium substitution is conducted to decrease this phase transition temperature. A single crystal of strontium substituted CMS, with nominal chemical composition Ca 1.7 Sr 0.3 MgSi 2 O 7 (CSMS30), shows no phase transition when temperature rises from room to melting temperature. Its piezoelectric d¤ 31 constant is 2.1 pC/N and its compressive strength is 830 MPa on crystal substrate with (ZXt)45°cut. The CSMS30 single crystal is a superior candidate material for pressure sensors at high operating temperatures.
Ba 3 TaGa 3 Si 2 O 14 (BTGS) bulk single crystals were grown by the Czochralski method. The crystal structure of BTGS has been refined using single-crystal X-ray diffraction data with a precision corresponding to an R index of 0.018. The crystal structure is isostructural to La 3 Ga 5 SiO 14 which has the trigonal space group P321 and Z = 1, and the distribution of each cation is ordered in each site. Material constants and resistivity of the crystal were measured up to 550 °C. The results indicate that the BTGS crystal is a good candidate for piezoelectric applications in elevated temperatures.
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