H - Pa (Hydrogen - Protactinium)

Condensed Phases

The H-Pa system has been investigated at temperatures up to 520°C and pressures up to 10⁷ Pa [84War, 85Has]. Three solid phases have been found in the temperature range 230-520°C: a solid solution of hydrogen in protactinium, a hydride with a homogeneity PaH_1.3-PaH_1.7 and the MgCu₂ type crystal structure, and the hydride with a homogeneity range PaH_2.0-PaH_3.0 and a β-UH₃ type crystal structure. Protactinium hydride with a α-UH₃ type structure was also found at temperatures below 230°C. However, its stability was not determined and it is possibly metastable.