Growth technology of piezoelectric langasite single crystal

Although langasite (La3Ga5SiO14) is an incongruent material, it can directly grow from the “pseudo-congruent melt” via the Czochralski method using a langasite seed crystal when the appropriate supercooling is provided. This may be explained by the extension of the univariant line of langasite+liquid into the primary phase field of Ga-containing lanthanum silicate. Free energies serving to solute transport, growth kinetics, surface creation and defect generation are summed up to be the total supercooling necessary for growth which may be larger for the formation of Ga-containing lanthanum silicate and smaller for langasite than the actual supercooling. The growth technology of 4-in-size crystal along [0 1 1¯ 1] is optimized by understanding (i) the importance of the prior annealing of the melt to acquire the suitable supercooling for growth, (ii) the transform of the unstable growth interface, (0 1 1¯ 1), into the complex of more stable principal planes, and (iii) the necessity of the accurate evaluation method to examine the homogeneity of the grown crystal. Issues of (i) and (ii) are interrelated. Physical crystal properties at high temperature are also demonstrated.