Role of oxygen vacancy and grain boundary energy in stability of tetragonal and cubic pure zirconia powders

Abstract

The mechanical treatment of monoclinic zirconia in high energy planetary ball mill reduces the grain size, increases microstrain, causes phase transition to metastable nanostructured tetragonal or cubic phases and produce considerable amounts of amorphous phase. Annealing of ball milled zirconia in chlorine atmosphere causes amorphous phase to be crystallised and change into cubic and tetragonal phases and also produces oxygen vacancy in zirconia (ZrO2‐x). Transmission electron microscopy observations suggest that the cubic phase has 19 nm diameter at least and reveal that zirconia particles have plenty of grain boundaries although the surface area measurements (Brunauer–Emmett–Teller) of cubic phase showed a lower critical surface area. Under this condition, the grain boundary energy and oxygen vacancy have an important role in the stability of tetragonal and cubic phases. The chlorine atmosphere increases the stability temperature of cubic and tetragonal phases up to 800 and 1000°C respectively.