A High-Pressure Structure in Curium Linked to Magnetism

Abstract

Curium lies at the center of the actinide series and has a half-filled shell with seven 5f electrons spatially residing inside its radon core. As a function of pressure, curium exhibits five different crystallographic phases up to 100 gigapascals, of which all but one are also found in the preceding element, americium. We describe here a structure in curium, Cm III, with monoclinic symmetry, space group C2/c, found at intermediate pressures (between 37 and 56 gigapascals). Ab initio electronic structure calculations agree with the observed sequence of structures and establish that it is the spin polarization of curium's 5f electrons that stabilizes Cm III. The results reveal that curium is one of a few elements that has a lattice structure stabilized by magnetism.

Structural investigation of californium under pressure

“…In the case of curium 6 an additional monoclinic (Cm III) high pressure phase was discovered between 37 and 56 GPa which was found to be stabilized by the spin polarization of curiums 5f electrons. Subsequent investigations into the high pressure behavior of curium-berkelium alloys 16 as well as previous studies on americium-curium alloys 17 have shown the Cm III phase to be unique in the sense that dilution of curium with its near neighbors is sufficient to prevent its formation.…”

“…Previous studies on these elements from americium 4,5 to curium 6 have shown a remarkable diversity of crystallographic structures which appear under pressure due to the influence of this 5f electron participation. Atomic volumes are also affected by 5f electron bonding across the actinide series with smaller volumes observed in the Pa to Pu metals which result from additional 5f bonding already being present at ambient pressure.…”

On the electronic configuration in Pu: spectroscopy and theory

“…As will be discussed below, there is very strong evidence that Am has n = 6. Additionally, recent measurements on Cm [24] indicate that n = 7 for Cm, within an LS like coupling scheme. The return to an LS van der Laan and Thole [25], which has been used to explain the cross-sectional behavior of the lighter actinides.…”

“…This is consistent with a close to 5f 6 configuration in Am as discussed in previous section. Recent high-pressure diamond-anvil-cell experiments for Am and Cm [24] reveal several phase transitions under compression. Am and Cm behave relatively similarly under pressure with the striking exception of a monoclinic (C2/c) phase in Cm (CmIII).…”

First-principles study of surface properties of PuO2: Effects of thickness and O-vacancy on surface stability and chemical activity

“…Besides playing an important role in both technological applications and environmental issues, Pu metal and its oxides show many intricate physical behaviors due to the complex electronic structure properties of 5f states [1][2][3][4]. Therefore, a thorough understanding of the physical and chemical properties of PuO 2 is of great significance, full of challenges and has always attracted attention.…”