Chemical vapour transport (CVT) was selected for the crystal growth method as it is appropriate for materials with high melting points and low vapour pressures such as ZnO and Ga 2 O 3 . Advantages include that high purity crystals can be obtained as, due to the closed nature of the growth system, minimal external impurities can be incorporated into the crystals. A sealed quartz ampule was employed using Cl 2 as a transport agent. The Cl 2 was added to the transport ampule via an evacuation rig similar to that described by Binnewies et al. The tube was sealed at a length of 15 cm and placed horizontally at the centre of a two-zone furnace set at 1100 °C and 1000 °C. Since the reaction is endothermic the precursor was placed at the hot end of the ampule. After 200 hr, the powder was fully transported to the cold end in the form of single crystals adhered to the ampule walls.