DEFECTS AND DIFFUSION IN PYROCHLORE STRUCTURED OXIDES

We present the results of static lattice energy minimisation calculati ons investigating the defect structure of pyrochlore structured oxides of general formula A(2)B(2)O(7) (A = Gd,Y;B = Zr,Ti). Our calculation s indicate that ionic motion will be effected predominantly by a vacan cy hopping mechanism between 48f sites. We also show that cation disor der is necessary for the thermal generation of anion vacancies on thes e sites. We find low solution energies for certain aliovalent dopants confirming the possibility of generating substantial concentrations of extrinsic defects. Approximate calculations of the electronic band ga ps, based on a small polaron model, give good agreement with measured values. (C) 1998 Elsevier Science B.V. All rights reserved.