New polymorph of HfMo₂O₈ synthesized using a high-pressure and high-temperature toroid anvil setup

Abstract

We report the synthesis and characterization of a new polymorph (β ) of HfMo₂O₈. This phase is synthesized from the trigonal (a) HfMo₂O₈ by application of high pressures and high temperatures. The sample obtained is characterized by powder x-ray diffraction (XRD) and the details of high-pressure and high-temperature phase are explained. The Rietveld analysis of the powder XRD data reveals that the β -HfMo₂O₈ crystallizes in a monoclinic lattice with unit cell parameters a=11.4138(6), b=7.9105(4), c=7.4395(3), and β =122.35(0)° . The β -HfMo₂O₈ is found to be isostructural to the room-temperature phase of β -ZrMo₂O₈. The coordination numbers of Hf and Mo atoms with oxygen atoms are eight and five, respectively. The nature and sharing of Hf and Mo polyhedra are entirely different in β modification compared to that in the α phase.