MOLECULAR-DYNAMICS STUDIES OF YTTRIA STABILIZED ZIRCONIA .2. MICROSCOPIC MECHANISM OF OXYGEN DIFFUSION

The microscopic mechanism of oxygen diffusion in yttria stabilized zirconia (YSZ) is investigated by means of a polyhedron analysis. It is shown that the probability of finding 0 ion in a tetrahedron increases as Y ions at the comers of the tetrahedron increase, and this tendency becomes marked with increasing dopant concentration, which is consistent with the fact that the oxygen coordination number for Y ion is larger than that for Zr ion. By studying the oxygen migrations between tetrahedra in the [100] direction in detail, it is found that the migrations preferentially occur between tetrahedra having a common Zr-Zr edge, and Y ions restrict the diffusion paths of 0 ions. The restriction by the Y-Y edge causes the decrease of the oxygen diffusion with increasing dopant concentration. It is discussed that the fluorite structure of YSZ is guaranteed by the defective and disordered state of oxygen sublattice.