Crystal Structure of Monoclinic Hafnia and Comparison with Monoclinic Zirconia

Abstract

The crystal structure of monoclinic HfO 2 was determined using Weissenberg techniques. Data were obtained from a needlelike single crystal which was grown from a lithium molybdate melt. The crystal was rotated about the α axis, and reflection data were obtained for nine levels. A three‐dimensional least‐squares refinement confirms that monoclinic hafnia is isomorphous with monoclinic zirconia. The atomic coordinates in the structures agree within one standard deviation. Thus, the fractional coordinates for the metal atom differ by less than 0.0005 and those for the oxygen atoms by no more than 0.01. Whereas three of the seven Hf–O distances are larger than the corresponding Zr–O distances, the average value is approximately 0.01 Å smaller. The average metal‐metal distance is approximately 0.02 Å less in HfO 2 than in ZrO 2 .