High pressure studies on uranium and thorium silicide compounds: Experiment and theory

Abstract The actinide silicides ThSi, USi and USi 2 have been studied under high pressure using both theory and experiment. High pressure synchrotron X-ray diffraction experiments were performed on polycrystalline samples in diamond anvil cells at room temperature and for pressures up to 54, 52 and 26 GPa, for ThSi, USi and USi 2 , respectively. At ambient conditions, the uranium silicides crystallize in tetragonal structures (space groups: I4/mmm for USi and I4 1 /amd for USi 2 ), while ThSi adopts an orthorhombic structure (space group: Pbnm) (including an anharmonic analysis of the silicon). These structures are found to be stable with no structural transitions observed up to the highest pressures achieved. The zero-pressure bulk modulus B 0 and its pressure derivative B 0 ′ at ambient pressure are obtained from the measured P – V relations. The experiments are accompanied by first principles calculations using the full-potential linear muffin-tin orbital method within the generalized gradient approximation for exchange–correlation effects. Experimental results are well reproduced by the calculated equation of state and ground state properties.