Interface field-modified solute partitioning during Mn: LiNbO₃ crystal fiber growth by micro-pulling down method I. Axial distribution analysis

During the growth of Mn : LiNbO₃ crystal fiber by the micro-pulling down method, the solute partitioning is greatly influenced by the interface electric field mainly caused by the large temperature gradient at the interface. This was experimentally and analytically studied for the initial transient, steady-state and terminal transient solute redistribution based on the concept of a field-modified partition coefficient, k_E0, and an effective growth velocity, V_EL. The field-modified effective partition coefficient, k_E, becomes larger than unity in the steady state although its equilibrium partition coefficient, k₀ < 1.0, which consequently leads to the Mn concentration deficiency in the solid during the terminal transient. There is a critical growth velocity, V*, below which the effective growth velocity, V_EL, and the field-modified equilibrium partition coefficient, k_E0, take negative value in which cases the positive ions such as Mn⁴⁺ move away from the interface.