In this research, a thermodynamic model used to describe the growth of  single crystals by chemical vapor transport technique with iodine as the transporting agent. The optimum growth condition in the  system has been predicted theoretically based on partial of different components. Some experiments were carried out for growing  crystals by the chemical vapor transport method using iodine as a transporting agent in the closed ampoule under various conditions. The experimental results showed that the  single crystals, which have been grown with growth parameters close to the theoretically predicted optimum growth conditions, have better quality in comparison with crystals grown under other conditions.