Synthesis and X-Ray Structural Analysis by the Rietveld Method of Orthorhombic Hafnia

Abstract

Monoclinic hafnia (HfO₂) powders were treated from 400° to 1100°C and at a pressure from 3 to 6GPa. The products were identified by powder XRD. The results indicated that an orthorhombic phase was synthesized at pressures above 4GPa in the temperature range from 400° to 1000°C. Although the monoclinic-orthorhombic transition pressure is almost the same as that of ZrO₂, orthorhombic HfO₂ is more stable at high temperatures than ZrO₂. The Rietveld analysis showed that the orthorhombic HfO₂ is isostructural with one of the two orthorhombic ZrO₂ (ortho I).