Formation and electronic properties of palladium hydrides and palladium-rhodium dihydride alloys under pressure.

We present the formation possibility for Pd-hydrides and Pd-Rh hydrides system by density functional theory (DFT) in high pressure upto 50 GPa. Calculation confirmed that PdH in face-centered cubic (fcc) structure is not stable under compression that will decomposition to fcc-PdH and H. But it can be formed under high pressure while the palladium is involved in the reaction. We also indicate a probably reason why PdH can not be synthesised in experiment due to PdH is most favourite to be formed in Pd and H environment from ambient to higher pressure. With Rh doped, the Pd-Rh dihydrides are stabilized in fcc structure for 25% and 75% doping and in tetragonal structure for 50% doping, and can be formed from Pd, Rh and H at high pressure. The electronic structural study on fcc type Pd RhH indicates the electronic and structural transition from metallic to semi-metallic as Pd increased from x = 0 to 1.