New ordered langasite structure compounds-crystal growth and preliminary investigation of the material properties

Langasite (LGS) and two of its isomorphs, langatate (LGT) and langanite (LGN), have attracted much attention for their potential for SAW and BAW applications. Their major attributes include higher electromechanical coupling than quartz, existence of temperature compensated orientations, high intrinsic acoustic Q, and that they melt congruently, thus feasible for mass production. Unfortunately the crystal structures of these compounds are disordered, leading to degraded (from ideally achievable) acoustic Q and electromechanical coupling, and nonuniform as well as hard-to-reproduce material properties. A new class of langasite isomorphs has recently been reported. These new compounds are totally ordered, and have all the positive attributes of LGS, LGT and LGN. The totally ordered structure promises higher achievable acoustic Q and maximal electromechanical coupling, and readily reproducible material properties. The reduced Ga-content among these crystals promises also lower material cost. This paper describes the crystal growth process and results of some preliminary material property investigation of the four new crystals, CNGS, CTGS, SNGS and STGS. Comparisons with quartz, LGS, LGT and LGN are also made, and device prospects explored.