Advances in design, growth and application of piezoelectric crystals with langasite structure

Crystals with langasite structure consist of more than one hundred compounds. Only about 20 compounds are grown and characterized. In this work, we first use first-principles calculation to simulate the crystal structure of 29 ordered langasite compounds and then forecast their piezoelectric related properties including dielectric constants, elastic constants, piezoelectric coefficients and electromechanical coefficients. Four known ordered crystals including SNGS, STGS, CTGS, CNGS, and several novel crystals including BTGS, CTAS, CNAS were grown by Czochralski method and characterized at room temperature and at high temperature from 400 to 900°C. The experimental results of piezoelectric properties verified the validity of theoretical forecast and that errors between experimental and theoretical results were in reasonable range. Gallium-free crystals shown good prospect in application of piezoelectric sensors, combining the advantages of low cost of raw materials and high performance. More efforts should be paid to the growth of these novel crystals.