The imposition of an external electric field on a growth system affects the crystallization process in two manners: (i) the thermodynamic effect and (ii) the growth-dynamic effect. The former modifies the chemical potentials of associated phases in equilibrium which could convert the incongruent-melting state into congruent-melting state. Langasite (La3Ga5SiO14), an incongruent-melting material in the ternary system of La2O3-Ga2O3-SiO2, became congruent-melting under an external electric field of 600V/cm. This conversion was attributed to the inversion of the stability relationship in terms of the molar free energy between the primary phase in equilibrium with liquid and the liquid phase at the composition of langasite. Such a transformation is generally possible when the electrical permittivities of liquid, primary phase and incongruent-melting material increase toward the end component of the primary phase. (c) 2005 Elsevier B.V. All rights reserved.