According to the theoretical foundations [1-3], let us regard the stable phases of the system Al2O3-Tl2O3.They are TlAl3O6, TlAl7O12, TlAl11O18 and produced with the peritectic transformation from molten state [4] in correspondence with the ionic interactions for Tl3+, Al3+, AlO2.The hexagonal crystal cell of aluminum oxide is characterized with closed packed symmetry and the thallium ion 3+ becomes the place of Al3+, isomorphic exchanging the sub-lattice of Tl3+ + 3· AlO2-.