The crystal structure of actinium metal and actinium hydride

Phase transitions of actinium dihydride: Pressure-induced charge transfer driving effect

“…larger than that of the Fm-3m phase. This enthalpy value confirms the stability of the Fm-3m phase under ambientpressure, in consistent with experimental observation [24]. At 200 GPa, the difference between the enthalpies of decomposition and P6/mmm phase, which is the most stable phase at this pressure, increases to 1.894 eV/f.u., thus validating the stability of AcH 2 under high pressure.…”

“…The enthalpies of the decomposition case, combining Fm3m Ac [24] with P6 3 /m H 2 [49], are larger than those of the stable phase at each pressure, as shown in Fig. 1.…”

“…With the only knowledge of chemical compositions, the experimental ambient-pressure fcc Fm-3m structure can be correctly reproduced [24], justifying the validity of CALYPSO methodology used in the structural searches of AcH 2 . In addition to the known Fm-3m structure, five competitive structures with different symmetries were selected from a large set of structures.…”

“…The preparation of actinium hydride has been reported by Farr et al [24] The product was obtained at microgram level as a mixture of Ac metal and KCl after the reduction of AcCl 2 by K at 350 C. By comparing its X-ray diffraction patterns with the LaH 2 analog, actinium hydride has been suggested to adopt a face-centered cubic (fcc) structure with a H/Ac ratio of approximately two. During the hydrogenation reaction to a dihydride, the volume of Ac metal lattice expands by approximately 22%, which is common in fcc rare-earth metal dihydrides [25e28].…”

Preparation, properties, and some recent studies of the actinide metals

“…AcCl_ with K metal vapor [13], on the milligram scale by reducing AcF_ with Li metal [14], and by reduction of Ac^O, by Th metal [15,16].…”