[8p-A201-1~7] 15.1 Bulk crystal growth

[8p-A201-1] [INVITED] New Directions of Crystal Growth by Controlling Degrees of Thermodynamic Freedom

〇Satoshi Uda¹ (1.IMR, Tohoku Univ.)

Keywords:oxide, degrees of freedom, stoichiometry

Increasing the degrees of freedom in growth system is useful to develop new crystals and new growth methods, which is not possible by simple replacement of elements in a crystal or design change of growth equipment for better crystal growth. For instance, in addition to conventional phase diagram parameters, i.e., temperature and composition, introducing external forces such as electric field, magnetic field or stress-strain field will bring one more freedom in the system to extend invariant point to univariant line or univariant line to divariant surface, or to change phase equilibrium relationship resulting in, for instance, the transformation of incongruent-melting state to congruent-melting state. The degree of freedom is determined by subtracting number of constraints from that of parameters. When one carefully examines them, one can obtain new understanding of physical phenomena associated with crystal growth.
In this talk, three topics will be presented in association with the degrees of freedom applied to growth system. The conversion of incongruent-melting state langasite (La₃Ga₅SiO₁₄) to congruent-melting state by applying high electric field will be discussed. Next a new concept of stoichiometry has been developed and a new stoichiometric LiNbO₃ doped with MgO having congruent composition has been obtained by finding non-negative freedom in each site of LiNbO₃. Thirdly, it is experimentally proved that the oxygen to metal stoichiometric relation is not valid in the diffusion boundary layer in the oxide melt, which suggests that oxygen is an independent component yielding one more freedom to vary populations of ionic species in the melt at the interface.