CDW state in U(Pt,Ir)2Si2

The dual nature of 5f electrons in uranium compounds, partially localised, partially itinerant, has long been known to play a pivotal role in their fundamental behaviours. Recently, a charge density wave (CDW) state was found in UPt2Si2 where 5f localisation is expected and is similar to REPt2Si2 analogues. The isostructural compound UIr2Si2 with delocalised 5f states does not exhibit a CDW state indicating a Mott transition between the Pt and Ir terminal phases, an observation seen in bulk studies. As such, the CDW state is a sensitive indicator of the 5f character. An investigation of the U(Pt,Ir)2Si2 series should provide a unique window into 5f (de)localisation and the effect on charge ordering mechanism, which has not been conclusively determined. Preliminary diffuse scattering studies for 5at.% Ir show that the CDW state is preserved. The planned experiments will investigate behaviour in the 5,10,15,20 at.% systems using both diffuse and inelastic x-ray scattering.