A decrease of the resistance is observed in crystals of the superionic material yttria stabilized zirconia (YSZ) when the crystals are reduced during the application of an electric field. The electric field causes the crystal to lose oxygen and applied temperature accelerates this loss. Essentially, the loss of the oxygen results in the removal of O2-ions from the lattice, each of which is replaced by two electrons and a vacancy which results in a doubly occupied vacancy. Arguments are put forth to show that as the concentration of doubly occupied vacancies increased, the mean energy of this band is raised due to lattice relaxation. Eventually, part of this band decays into valence band which results in its new energy states. In this article, we showed that electrical treatment induces a relaxation in the lattice. This relaxation is associated with a reduction in lattice tetragonality. Hence, generation of the tetragonal metastable phases is proposed as a result of applying an electric field through YSZ material. (C) 2010 Elsevier B.V. All rights reserved.