Comparative NMR study of hybridization effect and structural stability inD022-typeNbAl3and

Chin‐Shan Lue

¹

,

T. H. Su

²

,

Bingxing Xie

³

et al.

Abstract

With the aim of providing experimental information for the correlation between p-d hybridization and phase stability in the D0 22 structure, we performed a comparative investigation on NbAl 3 and NbGa 3 using 93 Nb NMR spectroscopy. The quadrupole splittings, Knight shifts, and spin-lattice relaxation times ͑T 1 's͒ for each individual compound have been identified. The larger quadrupole interaction and higher anisotropic Knight shift have been observed in NbAl 3 , indicative of the stronger hybridization effect for this material, as compared with its isostructural compound NbGa 3 . Results of experimental T 1 together with theoretical band structure calculations provide a measure of d-character Fermi-level density of states N d ͑E F ͒ and an indication of orbital weights. In addition, we found evidence that N d ͑E F ͒ correlates with the structural stability of the studied materials. Our NMR measurements confirm that NbAl 3 is more stable than NbGa 3 with respect to the D0 22 structure, attributed to the stronger p-d hybridization in the former material.

The native point defects in C14 Mg2Ca Laves phase: A first-principles study

“…In the anti-site defect Ca Mg1 structure the pseudo-gap almost disappears. Because the pseudo-gap at Fermi level indicate the presence of the directional covalent bonding and the enhancement of the bonding strength of material in comparison with the pure metallic bonding, the Fermi level closer to the bottom of pseudo-gap implies a stronger stability of system [44]. Therefore, our present results show the eventually weaker stability from Mg Ca to Ca Mg2 and Ca Mg1 , being consistent with the results of the defect formation energy.…”

Defusing Complexity in Intermetallics: How Covalently Shared Electron Pairs Stabilize the FCC Variant Mo2CuxGa6–x(x≈ 0.9)

“…A common feature of most earlier analyses of the TiAl 3 type is the prominence of covalent interactions between the T and E atoms. 18,19,21,48 The raMO functions of Figures 3−6 confirm this conclusion, as each reconstruction of a T atomic orbital appears with substantial in-phase contributions from neighboring E atoms. This observation extends to the shared electron pairs along the T−T contacts, where the bridging E atoms play a key role in stabilizing the electron pairs.…”

“…The Fermi energy (E F ) of the NbGa 3 structure sits comfortably in a pseudogap in the structure's electronic DOS distribution, as has been noted previously. 21 On moving from NbGa 3 to the hypothetical MoGa 3 structure, the DOS distribution is largely unchanged, with an analogous pseudogap still occurring at 14 electrons/T atom. However, the replacement of Nb with Mo has increased the phase's electron count from 14 to 15 electrons/T atom.…”

First-principles study of point defects in C14 MgZn2 Laves phase

“…The hybridization between Mg and Zn is also clear in entire region. Also, Fermi level falls into a small local minimum in the bottom of pseudo-gap in perfect MgZn 2 structure, indicating the presence of the directional covalent bonding and the enhancement of the bonding strength of material in comparison with the pure metallic bonding, so the Fermi level located at the valley bottom of pseudo-gap implies a strong stability [45]. The present results are fairly consistent with other studies [7,14].…”