NMR study of trialuminide intermetallics

Abstract

We present a systematic study of the DO 22 -structure trialuminide intermetallic alloys using 27 Al NMR spectroscopy. The quadrupole splittings, Knight shifts, and spin-lattice relaxation times on Al 3 Ti, Al 3 V, Al 3 Nb, and Al 3 Ta have been identified. Knight-shift tensors were isolated by observation of quadrupole satellite lines and fitting to the central-transition powder patterns. The results are associated with the local electronic density of states for each crystallographic site. Universally small isotropic Knight shifts and long T 1 's are consistent with low Fermi-surface densities of states indicating the importance of Fermi-surface features for the phase stability of these alloys. Larger anisotropic Knight shifts occurring at aluminum site I indicate strong hybridization at this site, and the electric-field-gradient tensors confirm the strong ab plane bonding configuration. Local-moment magnetism is found in Al 3 V, yet electrically this material appears very similar to the other DO 22 aluminides. ͓S0163-1829͑98͒07112-4͔

and MAS NMR and multiple quantum studies of Ti-doped NaAlH4

“…However, the observed TiAl 3 is paramagnetically shifted, which means that paramagnetic shielding adds to the overall magnetic field experienced by the nucleus. This is similar to other static 27 Al NMR data [24].…”

Comparative NMR study of hybridization effect and structural stability inD022-typeNbAl3andLue1, Su2, Xie3 et al. 2006Phys. Rev. B

“…This interpretation is consistent with the previous 27 Al NMR studies of the D0 22 trialuminides, which pointed to larger directional bonding between transition metal and Al site-I. 7 Thus, due to the covalent interaction between Al/ Ga-p and Nb-d electrons, both NbAl 3 and NbGa 3 should be considered as poor metals with covalent characters. …”

“…Hence, the possible mechanisms driving the atomic ordering have attracted a large number of investigations, focused on electronic properties in the related alloys, to elucidate their structural phase stability. [1][2][3][4][5][6][7][8][9][10][11] Theoretically electronic structure calculations have been performed to understand the stable phase in several D0 22 -type transition metal trialuminides. [12][13][14][15] The calculated total density of states ͑DOS͒ exhibited a deep valley in the vicinity of the Fermi level, attributed to the hybridization between Al-p and M-d playing an important role for the DOS reduction.…”

25Mg NMR site analysis in metals and intermetallics

“…Recent reports [1][2][3][4][5][6][7][8] have highlighted the valuable role that NMR has to play in the identification and quantitation of precipitate phases in lightweight aluminium and magnesium based alloys. Some of these phases, which are binary or ternary intermetallic compounds of the dilute alloying elements with the Al and Mg host, and present in the host lattice in concentrations of order or less than 1 mol%, have been identified by their 27 Al, 45 Sc and 63 Cu NMR spectra [5][6][7][8].…”