The phase diagram of the CeH2 system

A peritectic phase diagram has been proposed by Libowitz et al. based on sparse measurements of several authors. On the contrary Toguchi et al. proposed a critical point of the miscibility gap. We have performed P-T-x measurements in the range of 820–1150°C and constructed the CeH 2 phase diagram. The location of the phase boundaries have been determined by applying a constant slope criterion Δlog P(H 2 )/Δlog x H to the P-x curves. The results confirm the peritectic behaviour, but show appreciable differences in the position of the phase boundaries. The peritectic temperature occurs at 1025°C and reflects a substantial increase in the melting point of cerium (795°C) with increasing dissolution of hydrogen (up to ∼40%). Single crystals of CeH 2.95 have been grown by precipitation from a hydrogen saturated melt above the peritectic point. Optical reemission measurements of CeH 2.95 show an absorption edge corresponding to a band-gap of ΔE = 1.54 eV.