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The Effect of an External Electric Field on Phase Equilibria, Nucleation and Growth
Tohoku University, Institute for Materials Research (IMR), 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan
Regarding a new growth method, it may be differentiated into two classes. One is associated with a simply technological improvement and the other is a fundamental reform of crystal growth. The former includes, for the case of melt growth via the Czochralski technique, the optimization of temperature distribution and gas flow in a furnace, rotation and pulling rate, etc., which I would say is a simple manipulation of growth conditions. In contrast the latter could bring a radical change of crystal growth based on scientific principles, which would be more interesting.
Applying an external electric field to the growth system is one of the latter cases and leads to a completely new growth approach since it creates one more freedom in terms of Gibbs phase rule, which would allow us to move from invariant to univariant or univariant to divariant, etc. Such an increase of freedom enables us to change equilibrium phase relationship, that is, the conversion of incongruency to congruency of a compound.
There may be two ways to apply an electric field to the growth system. One is concerned with an electrostatic field applying through the inert gas that is an electrically -insulating phase [1,2]. Because oxide melts or protein solutions show high ionic conductivity, the electric potential distribution is nearly flat in them even if an electric field as large as several-hundred V/cm is electrostatically applied. However, the imposition of such an external electric field would form an electric double layer (EDL) of ~nm width between two different substances, i.e., crystal and melt or solution. This is the place where a large electric field of 104 to 105 V/cm could be sustained, which modifies phase relationship, nucleation and growth .
The other is a direct injection of an electric current to the solid-interface-liquid . Because of the resistivity of the melt or solution, the injected current generates an electrical potential distribution leading to an electric field with the order of ~ 1 V/cm. It should be noted that the current injection also induces the adsorption or rejection of ionic solute at the interface, which would make solute behavior at the interface a little more complicated.
Application of an external electric field on the crystallization process modifies the chemical potentials of associated phases leading to two distinct consequences: (i) thermodynamic effect and (ii) growth-dynamic effect. The former pertains to the macroscopic picture and changes the equilibrium phase relationship, while the latter is on a microscopic scale and modifies the solute transport, nucleation, growth kinetics, surface creation and defect generation related to crystal growth.
We demonstrate the former case that the electric field converted the incongruent-melting state of langasite (LGS: La3Ga5SiO14) into congruent-melting state  and the latter case that the electric field changed the critical nucleation energy resulting in the control of nucleation rates of the hen-egg white lysozyme . It should be also noted that such an energy shift is dominated by the magnitude of electrical permittivities of solid and liquid phases and their compositional dependence. By varying frequency of an applied field, we see that these dominant parameters could change the nucleation of lysozyme .
The current injection to the interface of growing Mn:LiNbO3 controls Mn distribution in the grown crystal for which the equilibrium partition coefficient, k0 of Mn into LiNbO3 crystal should be replaced with the field-modified partition coefficient, kE0.
 S. Uda, X. Huang and S. Koh, J. Cryst. Growth 281 (2005) 481.
 H. Koizumi, S. Uda, K. Fujiwara and J. Nozawa, Langmuir 27 (2011) 8333.
 S. Uda, S. Koh and X. Huang, J. Cryst. Growth 292 (2006) 1.
 S. Uda and T. Tsubota, J. Cryst. Growth 312 (2010) 3650.
Presentation: Invited oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Topical Session 8, by Satoshi Uda
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17
Submitted: 2013-03-22 06:56 Revised: 2013-04-26 01:58