B-11 NUCLEAR-QUADRUPOLE INTERACTION IN METAL HEXABORIDES (MB6)

The magnitude of the electric field gradient at the boron nucleus, |eq|, in divalent- and trivalent-metal hexaborides (MB6) as well as in mixed-valent SmB6 has been measured by the nuclear magnetic resonance method. In each group of divalent- and trivalent-metal hexaborides, |eq| decreases remarkably with increasing lattice parameter. At a given lattice parameter, |eq| for the trivalent-metal hexaborides is smaller than that for the divalent-metal hexaborides. The value of |eq| for SmB6 is situated between those for the divalent- and trivalentmetal hexaborides. On the basis of these results, the electronic structure of the hexaborides is discussed. © 1979.