Peculiar properties of UMB₄ (M = V, Cr, Mo, W) uranium borides

ABSTRACT

UMB₄ (M = V, Cr, Fe, Co, Mo, W, Re, Os) materials prepared by arc-melting have UMB₄ as the main phase, with (V, Cr, Fe, Co) crystallising in the YCrB₄ structure type, while (Mo, W, Re, Os) adopt the ThMoB₄-type. For M = V, Cr, Mo, W the magnetic susceptibility is low and only weakly temperature dependent, but higher than α-U, which can be ascribed to a higher density of states at the Fermi level. Heat capacity results point to a very high Debye temperature for both structures, which is associated with very high lattice stiffness of the boron network. However, for W and Mo the boron vibrations are accompanied by low-energy Einstein modes coming from vibrations of the atoms inside the boron cages that could lead to superconductivity. The electronic structure of UMB₄ is influenced by a strong 5f-d hybridization and by the B-2p states, which explains the observed weak Pauli paramagnetism.

KEYWORDS:

• Uranium borides
• crystal structure
• magnetic susceptibility
• heat capacity
• ab initio calculations

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

S. Mašková http://orcid.org/0000-0002-0154-7951

L. Havela http://orcid.org/0000-0001-9801-7094

M. Diviš http://orcid.org/0000-0001-9425-0171

Additional information

Funding

This work was supported by the Czech Science Foundation under the grant No. 18-02344S and by funds from FCT under the Portuguese projects P2020-PTDC/FIS-NAN/6099/2014 and UID/Multi/04349/2013.