Study of the defect formation in KDP crystals grown under extremely high supersaturation

•Defect formation during fast growth.•X-ray topography as a method for studying structural defects in crystals.•Growth from solution at extremely high supersaturation and with a fast growth velocity.•2D nucleation mechanism KDP single crystal growth.

Crystals grown within the supersaturation ranges between σ=0.22 and σ=0.47 were investigated by X-ray topography. Within the supersaturation range between σ=0.22 and σ=0.34 the morphological type of striation was observed, whereas the kinetic type was observed at the supersaturation σ=0.44-0.47, the growth bands and sectorial boundaries being weakened. In case of a uniform seed regeneration the crystal grows almost defect-free. The calculation of the kinetic curves of KDP crystal growth shows that in the presence of dislocations the predominance of the mechanism of two-dimensional (2D) nucleation over the spiral growth is possible if the supersaturation is above σ=0.26 for the {100} faces and above σ=0.44 for the {101} faces. It is assumed that the conditions under which 2D nucleation growth mechanism is predominant have been achieved.