Iodine defect energies and equilibria in ZrO2

Abstract Incorporation energies and defect equilibria in monoclinic, tetragonal and cubic phases of ZrO 2 are predicted, using density functional theory calculations, for iodine dopant concentrations between 10 − 5 and 10 − 3 atoms per formula unit of ZrO 2 . Data are presented for monoclinic and tetragonal polymorphs, in the form of Brouwer diagrams, to show the defect response at oxygen pressures ranging from 10 − 35 to 10 0 atm. The oxygen pressure required for stoichiometry in monoclinic ZrO 2 is approximately 10 − 7.5 atm, at both low and high iodine concentrations, whereas for tetragonal ZrO 2 , it increases from 10 − 10 to 10 − 6.5 atm as the iodine concentration is increased from 10 − 5 to 10 − 3 atoms/formula unit. The dominant defects in monoclinic ZrO 2 are I O • charge-compensated by I ‴ Zr at low oxygen pressures, and a combination of I ‴ Zr , I O • • • and I i • defects at high oxygen pressures. In tetragonal ZrO 2 , the dominant defects at low oxygen pressures are e ′ , V O • • and I O • . At high oxygen pressures, h • and I ‴ Zr are dominant, with additional charge-compensation from V ″″ Zr defects when iodine concentrations are low. The concentration of I O defects in the tetragonal phase decrease with increasing oxygen pressure above stoichiometry, demonstrating competition between iodine and oxygen for occupancy of the anion site. This has implications for fuel and cladding designs that are resistant to iodine-SCC.