Volumetric study of the α→α′ phase transformation of cerium and its implications regarding the crystal structure of α′-cerium.

Abstract

The volume change of cerium metal at the α→α′ phase transformation at 51 kbar is found to be (1.5±1) % from macroscopic measurements made in the sliding-anvil apparatus SAD 2. This value supports the proposal by Zachiarasen and Ellinger that the high-pressure forms of cerium above 51 kbar are a stable orthorhombic form with the α-uranium type of structure and a metastable monoclinic body-centered form with a deformed face-centered structure and invalidate all the other crystal structures reported so far for α′-cerium.

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

“…Upon further compression at RT, Ce undergoes a phase transition, at ∼4 GPa. Early x-ray diffraction experiments reported that the transition is to a C-centered orthorhombic structure (oC 4 in Pearson notation and denoted α in the literature), isostructural with that found in α-uranium at ambient conditions [12,13]. Subsequent x-ray studies [14,15], however, concluded that Ce transforms to a C-centered monoclinic structure (mC 4 in Pearson notation and denoted α in the literature), while others observed both the oC 4 and mC 4 structures [16,17].…”

Optimization of stress in the anvils of an opposed-movement multianvil device

“…Under these conditions, calculations show that pressures of 20 GPa can be obtained. Experiments confirmed that pressures of 20 GPa could be reached in this device [21], but this pressure is expected to be the approximate limit for this kind of apparatus with tungsten carbide anvils.…”