The high-pressure, high-temperature phase diagram of cerium

Abstract

We present an experimental study of the high-pressure, high-temperature behaviour of cerium up to ∼22 GPa and 820 K using angle-dispersive x-ray diffraction and external resistive heating. Studies above 820 K were prevented by chemical reactions between the samples and the diamond anvils of the pressure cells. We unambiguously measure the stability region of the orthorhombic oC4 phase and find it reaches its apex at 7.1 GPa and 650 K. We locate the α-cF4–oC4–tI2 triple point at 6.1 GPa and 640 K, 1 GPa below the location of the apex of the oC4 phase, and 1–2 GPa lower than previously reported. We find the α-cF4 → tI2 phase boundary to have a positive gradient of 280 K (GPa)−1, less steep than the 670 K (GPa)−1 reported previously, and find the oC4 → tI2 phase boundary to lie at higher temperatures than previously found. We also find variations as large as 2–3 GPa in the transition pressures at which the oC4 → tI2 transition takes place at a given temperature, the reasons for which remain unclear. Finally, we find no evidence that the α-cF4 → tI2 is not second order at all temperatures up to 820 K.

High-pressure structure of praseodymium revisited: In search of a uniform structural phase sequence for the lanthanide elements

“…As said, the diffraction profiles we observed from the post-oC4 phase were simpler than those from the oC4 phase itself, suggesting they came from a structure with higher symmetry and/or with a smaller unit cell. Previous studies of the high-pressure behavior of Ce have reported similar simplifications of the diffraction profiles at the oC4 → tI2 transition [16,18,30,31], and comparisons of the diffraction profiles from tI2-Ce [16,31,32] with those observed in Pr above 200 GPa [Figs. 4(d) and 4(e)] showed them to be similar.…”

Noninteger Valence in Ce‐Based Compounds

“…with Θ as the Debye temperature. Using relation for entropy change (11) and knowing that Δv ¼ v 0 À v is volume change and ΔT ¼ T À T 0 , temperature change at phase transition relation (13) will be transformed into…”

Revisiting the effect of shear stress on the γ→α phase transition of cerium under shock loading

“…Detailed reviews of theoretical models, previous experiments and simulations can be found in Refs. [1,24,25].…”