A direct view on Ni substitution in Sc2Ir6-xNixB as probed by NMR

Abstract

Intermetallic borides, such as the Sc2Ir6-xNixB (x = 0–6) series, exhibit technologically relevant physicochemical properties, that are all associated to boron ordering. X-ray diffraction has not yet fully investigated the effect of Ir substitution by Ni on the boron arrangement of these borides, primarily due to its weak scattering factor. Herein we employ 11B-NMR to probe the boron ordering of Sc2Ir6-xNixB series at atomic scale, overcoming limitations on low-Z materials. Across the Ni-substitution range, the spectral parameters and spin-lattice relaxation rates (T1−1) were responsive to changes in crystal symmetry and valence charges. The spectral analysis and T1−1 vs. x reveal that Ni substitution causes phase separation at the nanoscale between ordered and disordered borides. For x = 3, T1−1 is T-independent, indicating a relaxation mechanism caused by paramagnetic centers whereas x = 5 follows a T2-dependence that is consistent with band structure predictions of a reduction in the density of states, correlated with sharp features near the Fermi level.