Extensive Investigation of High‐Pressure Tungsten Dioxide β‐WO2

Red single crystals of β‐WO2 were synthesized under high‐pressure/high‐temperature conditions of 13.1 GPa and 1693 K in a Walker‐type multianvil apparatus. β‐WO2 crystallizes in the space group Pnma (Z=12) with the lattice parameters a=9.7878(5), b=8.4669(4), c=4.7980(2) Å, and V=397.62(3) Å3. The structure consists exclusively of WO6 octahedra, forming a twinned distorted rutile type structure. Temperature dependent X‐ray powder diffraction measurements at normal pressure conditions revealed an irreversible phase transition from β‐WO2 to α‐WO2 between 1173 and 1223 K. Magnetic measurements showed weakly positive susceptibility values which increase to lower temperatures. This is caused by traces of paramagnetic impurities. DFT calculations predict β‐WO2 to be a semiconductor with an indirect band gap of about 0.6 eV.