High-pressure structural phase transitions in semiconducting niobium dioxide
Abstract
Niobium dioxide was studied up to 47 GPa by angle-dispersive, x-ray powder diffraction. Semiconducting α-NbO2 (space group I41/a, Z=32) was found to transform to β-NbO2 (space group I41, Z=16) above 5 GPa. Both phases have distorted rutile-type structures and the transition involves a change in the long-range ordering of the metal-metal bonds. A further transition was observed above 8 GPa to a baddeleyite-related structure with a=9.975(1), b=9.963(1), c=9.933(1) Å, β=104.023(4)°, and Z=32 at 12.8 GPa. The doubling of the unit cell along a, b, and c and the larger monoclinic angle with respect to a baddeleyite-type cell are due to the presence of metal-metal bonds. The d1 cation dioxide, NbO2, is thus shown to behave in a similar way to d0 cation dioxides, which follow a phase transition sequence involving the baddeleyite-type structure.
- Publication:
-
Physical Review B
- Pub Date:
- June 1999
- DOI:
- 10.1103/PhysRevB.59.13650
- Bibcode:
- 1999PhRvB..5913650H
- Keywords:
-
- 61.50.Ks;
- 61.10.-i;
- 62.50.+p;
- 81.30.-t;
- Crystallographic aspects of phase transformations;
- pressure effects;
- X-ray diffraction and scattering;
- High-pressure and shock wave effects in solids and liquids;
- Phase diagrams and microstructures developed by solidification and solid-solid phase transformations