Growth of high quality single domain crystals of langasite family compounds

Langasite family compounds have attracted a lot of attention because of the combination of a number of nice material properties such as high piezoelectric coupling, temperature compensation and low acoustic loss. Another very important property is that the compound melts congruently so that large single crystals of langasite can be produced by the conventional Czochralski melt pulling technique similar to that of LiNbO₃ and LiTaO₃. This makes the commercial scale production feasible. Nevertheless, despite the promises, the production of large commercial size langasite single crystal has always been erratic. We reported a year ago that langasite has both twinning and domain structure problems which were not recognized before. We developed the etching technique to reveal these crystal defects. In order to produce single domain crystals, a systematic process is established to screen the seed crystals so that the initial seed is twin-free, domain-free and low in dislocations. We also made special effort to reduce the temperature gradient within the growth chamber, since we have observed evidence of strain induced defects which an due to the growth anisotropy of the crystal. With all the changes in the growth process and growth environment, we are able to produce very high quality single domain crystals of the langasite family compounds including LGS, LGN and LGT