Ionic impurity transport and partitioning at the solid–liquid interface during growth of lithium niobate under an external electric field by electric current injection

Transport of ionic species in the melt and their partitioning at the solid–liquid interface during growth of lithium niobate was studied under the influence of intrinsic and external electric fields. A Mn-doped lithium niobate (Mn:LiNbO3) single crystal was grown via the micro-pulling-down (μ-PD) method with electric current injection at the interface. Mn ions were accumulated or depleted at the interface, depending on the sign of the injected current. The electric current injection induced an interface electric field as well as a Coulomb force between the interface and Mn ions. The electric field modified the transportation of Mn ions and their partitioning into the crystal, while the Coulomb force led to adsorption or rejection of Mn ions at the interface in addition to Mn concentration change due to the electric field. Effect of the Coulomb force was often observed to be larger on Mn concentration at the interface than that of the induced electric field, and dominated the redistribution of Mn in the solid. It has been experimentally and analytically shown that Mn concentration partitioned into the crystal can be obtained by multiplying Mn concentration at the interface by a field-modified partition coefficient, kE0, instead of the conventional equilibrium partition coefficient, k0.