Study of congruent-melting composition of langasite and its effects on crystal quality

Congruent-melting composition of langasite (La₃Ga₅SiO₁₄) was studied by a combination of melting-point measurement, crystal growth and compositional characterizations. The melting points of sintered samples with various compositions within the solid solution range determined by X-ray diffraction (XRD) around the stoichiometric composition were measured by differential thermal analysis (DTA). Upon the growth of single crystals from the compositions with the highest melting point, the compositions of various parts of the crystals and residual melts were investigated by X-ray fluorescence spectrum (XFS). The congruent-melting composition was determined to be the composition from which a minimum deviation of composition of both the crystal and the residual melt was obtained.