V51Quadrupolar Effects in V—Transition-Metal Alloys and Solutions of O and N in V

The ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ NMR in several V-based alloys with $3d$, $4d$, and $5d$ transition metals, and in dilute solid solutions of O and N in V, was used to study quadrupolar effects due to alloying. The results show these effects to be several times smaller for transition-metal (substitutional) solutes than for interstitial O and N in V. The solute dependence suggests that the field gradients around substitutional atoms arise mainly in response to local lattice distortion rather than to the shielding of the excess charge of the solute. A line-shape simulation based on an $r^{-3\mathrm{}}$ radial dependence of $q$ produces good agreement with the observed absorption spectra. The all-or-nothing wipeout model, when applied to the interstitial alloys, yields wipeout numbers $n_1=126\mathrm{}\pm 7$ for N in V, and $n_1=194\mathrm{}\pm 12$ for O in V. The observed magnitude of the effective field gradients in V-based alloys is believed to result from a partial cancellation of the Sternheimer antishielding tendency by the overshielding effect of a large density of states near the Fermi level at the V atoms.