Growth behaviour of potassium sodium niobate single crystals grown by solid-state crystal growth using K4CuNb8O23 as a sintering aid

The effect of addition of 0, 0.5 and 2 mol% K4CuNb8O23 liquid phase sintering aid on the growth of single crystals of (K0.5Na0.5)NbO3 by solid-state crystal growth (SSCG) was studied. Single crystal growth in the samples with 0 and 0.5 mol% K4CuNb8O23 was initially rapid and then tailed off with annealing time, due to matrix grain growth which reduced the driving force for crystal growth. Addition of 0.5 mol% K4CuNb8O23 caused a reduction in both single crystal and matrix grain growth rates. Addition of 2 mol% K4CuNb8O23 caused matrix grain growth to stagnate, resulting in an almost constant driving force and constant crystal growth during annealing. Single crystals grown using 0 and 0.5 mol% K4CuNb8O23 were stoichiometric, but single crystals grown with 2 mol% K4CuNb8O23 were Na-rich. This was due to lowering of the solidus temperature by addition of K4CuNb8O23.