Atomistic simulations of the coupled anion/cation disorder in this pyrochlore structure showed that the homo-atomic cation-vacancy migration energies ranged from 3.8 to 7.9eV, and increased upon adding anion defects. In the case of ordered materials, the energies for hetero-atomic Ti or Zr vacancy migration to Gd sites were 1.4 and 1.9eV, respectively. The addition of neighbouring O defects tended to reduce these energies to less than 1eV. The hetero-atomic migration of Gd vacancies to Ti or Zr sites remained above 2.7eV; even in the presence of O defects.

Cation Vacancy Energetics in the Gadolinium Titanate/Zirconate System. R.E.Williford, W.J.Weber: Journal of the American Ceramic Society, 1999, 82[11], 3266-8