Annealing of ZrO2 in a nitrogen atmosphere leads to a nitrogen contain
ing phase called beta '' phase having a trigonally distorted fluorite
structure with ordered anion vacancies. DTA/TG investigations indicate
d that the beta '' phase decomposes into m-ZrO2 above 500 degrees C re
leasing nitrogen during the reaction with oxygen. Prevention of oxygen
uptake by use of closed tantalum tubes instead of open platinum cruci
bles enabled the detection of a new reversible phase transition at sim
ilar to 965 degrees C. The thermoanalytical results have been confirme
d by high temperature-X-ray investigation.