Phase transition and compressibility study of UOs2 under pressure

High-pressure X-ray diffraction studies on MgCu2 type phase of UOs2 have been carried out up to 36 GPa. The compound remains in its parent phase up to 12 GPa with bulk modulus 261 GPa. Beyond 12 GPa, a first order phase transformation is observed. The phase transition is sluggish in nature and completes at 20.1 GPa. The high-pressure phase is found to be a hexagonal cell with lattice parameters a = 3.013 Å and c = 4.267 Å. Charge density calculations show that uranium tetrahedra in the lattice are responsible for the phase transition. The density of state plots at Fermi level, wherein a pseudogap originates at high pressures, confirms the existence of a high pressure phase and uranium site is found to contribute significantly to such changes in density of state. The retrievable high pressure phase is found to be the least compressible among uranium intermetallic compounds with bulk modulus of 366 GPa.