High Pressure X-Ray Diffraction Study of

Uranium manganese germanide, UMn2Ge2, crystallizes in body-centered tetragonal ThCr2Si2 structure with space group I4/mmm, a = 3.993Å and c = 10.809Å under ambient conditions. Energy dispersive X-ray diffraction was used to study the compression behaviour of UMn2Ge2 in a diamond anvil cell. The sample was studied up to static pressure of 26 GPa and a reversible structural phase transition was observed at a pressure of ∼16.1 GPa. Unit cell parameters were determined up to 12.4 GPa and the calculated cell volumes were found to be well reproduced by a Murnaghan equation of state with K0 = 73.5 GPa and K ' = 2 11.4. The structure of the high pressure phase above 16.0 GPa is quite complicated with very broad lines and could not be unambiguously determined with the available instrument resolution