The NMR and electric-field gradients in sigma phase vanadium alloys

Nuclear quadruple effects in the 51V and 59Co NMR in σ phase V-Co and V-Ni are studied for various alloying concentrations. Both 51V and 59Co spectra in V-Co are used to compare the quadrupole moments of the two nuclei and to reconfirm the ratio Q(59Co)/Q(51V) is approximately equal to 10. Local-environment effects are studied in quadrupole splittings of 51V resonance in both V-Co and V-Ni, and are compared with the calculated values taking into account only atoms on the coordinating polyhedron around the specific atomic site. The changes in the asymmetry parameter eta of the electric-field gradient at certain atomic sites sensitively reflect the local arrangement of atoms. The experimental values of e2qQ/h and eta for 51V are 2.6 MHz and about 0 for site II, and 2.2 MHz and about 1 for sites III and V. (author)