Growth habit control of ZnO single crystals in molten hydrous alkali solutions

Hexagonal prism-like and plate-like wurtzite zinc oxide (ZnO) single crystals have been grown in a molten hydrous alkali solution using the spontaneous nucleation method. It has been found that the growth habit of the crystals depends strongly on the basicity of the solution. In molten hydrous KOH solution, the highest growth rate of the crystal is along the +c-axis and slender hexagonal prisms were obtained. In molten hydrous KOH+LiOH or NaOH+LiOH solutions, the growth rate of the +c face slows down as more LiOH is introduced to the solution, resulting in the formation of thin hexagonal plates. This was confirmed by XRD analysis of the single crystals. We conclude that the growth habit of ZnO crystals can be successfully controlled by adjusting the basicity of the solution. It is proposed that there are two individual growth units, [Zn(OH)3(H2O)]− and [Zn(OH)4]2−, in the solution. The growth habit can be explained by the polar structure of the ZnO single crystal and the character of the growth units.

► Zinc oxide single crystals have been grown in a molten hydrous alkali solution.
► The crystals are in the shape of hexagonal prisms or hexagonal plates.
► The growth habit of the crystals depends strongly on the growth units.
► The growth units are [Zn(OH)3(H2O)]− and [Zn(OH)4]2−.
► The growth habit can be successfully controlled.