IMPROVING CRYSTAL RESONATORS WITH NEW MATERIALS.

Accurate time and frequency standards depend critically on crystal resonators made of quartz because this material has extremely low internal dissipation of mechanical energy. This dissipation is measured by the Q of the resonator which is typically about three million for a 5 MHz device. Achievement of this high a Q value was the result of extensive research in the 1950s into the mechanism of energy loss and the development of techniques to eliminate impurities and to grow more perfect crystals of quartz. Recently, a new class of synthetic crystals based on langasite--a lanthanum-galliumsilicate--and its isomorphs, langanite and langatate, have exhibited properties that could make them useful substitutes for quartz in many applications. However, the Q values are seldom as high as in properly prepared quartz. NIST has developed a novel method of measuring the Q of piezoelectric crystals that minimizes energy loss to the surroundings and, hence, can measure the internal dissipation with unusual accuracy. Appli cation of this method at a variety of temperatures and frequencies has exposed several mechanisms of internal loss in the langasite type materials and is being used to guide the development of manufacturing techniques that will insure the consistently high values of Q required for the next generation of crystal resonators.