Cation vacancy energetics in the gadolinium titanate/zirconate system

Atomistic simulations of coupled anion/cation disorder in the pyrochlore st ructure of Gd-2(ZrxTi1-x)(2)O-7 show that homoatomic cation vacancy migrati on energies range from 3.8 to 7.9 eV, and increase with the addition of ani on defects. For ordered materials, the energies for heteroatomic Ti or Zr v acancy migrations to Gd sites are 1.4 and 1.9 eV, respectively, but the add ition of neighboring oxygen defects generally reduces these energies to les s than 1 eV. The heteroatomic migration of Gd vacancies to Ti or Zr sites r emains rather large (>2.7 eV) even with the presence of oxygen defects.