ROLE OF ANION VACANCIES IN NITROGEN-STABILIZED ZIRCONIA

Introduction of nitrogen into zirconia creates oxygen vacancies in the anion sublattice as required by charge neutrality when N3- replaces for O2- in the structure, being similar to those obtained by lower valency cation substitution for zirconium. There is no essential structural difference between the cation-related vacancy and the anion-related vacancy, and their effects on the stabilization or zirconia are additive. The zirconia structure can, when formed in the Zr-Y-O-N system, tolerate a total of 6% of vacancies in the anion lattice without deviating from the original fluorite structure; above this limit, ZrN precipitates. Therefore, both partially and fully stabilized zirconia can dissolve a certain amount of nitrogen when these phases react with either atmospheric nitrogen or a solid nitride at high temperatures.