Высокотемпературные фазовые переходы в ZrO-=SUB=-2-=/SUB=-

. Analysis of the primary sources shows that there is only one reliable message about the observation of the cubic phase by x-ray method. This phase is observed at least 2500°C. All other reports on the observation of the phase transition in tetragonal modification at about 2300°C are reliable only regarding the existence of the transition at that temperature. But this is a transition to the t'-tetragonal phase. It should be concluded that at normal pressure ZrO2 has four polymorphic modifications: monoclinic (m), two tetragonal (t and t') and cubic (c), passing one to another with increasing temperature. Work is performed under partial support of RFBR grant 17-08-01227. The author is grateful to A.V. Kuzmin and V.B. Balakireva for valuable comments and assistance in the work.