Nuclear Magnetic Resonance in Transition-Metal Diborides

Abstract

Nuclear magnetic-resonance studies of the groups IV, V, and VI transition-metal diborides show that the boron nuclei have a small quadrupole coupling constant, and negative frequency shift of the order of 10—4. The V51 resonance in VB2 provides a measure of the quadrupole coupling constant for V51 as 2.35 Mc/sec and a frequency shift of —3.37×10—3. The frequency shifts are enhanced at low temperatures. These data are explained within the framework of a suggested metal—boron donor—acceptor bonds by proposing s—d exchange polarization and diamagnetic ``ring current'' contributions to the field at the nucleus.

NMR study of B‐2p Fermi‐level density of states in the transition metal diborides

“…As a consequence, no visible quadrupole edges have been detected with our static NMR probe. Such observations are consistent with previously reported results [17,18].…”

“…The observed shift is very small for each studied material, consistent with the published results [17,18]. We also performed the measurements at low temperatures, and no detectable change in NMR spectra and shifts were found, indicating the paramagnetic metallic character in these diborides.…”

“…Nuclear magnetic resonance (NMR) in metals provides a local probe, yielding information about the electronic structure near the Fermi surface. Although NMR results have appeared in some transitional metal diborides [17,18], a systematic study, especially for the spin-lattice relaxation time (T 1 ), is still missing. The aim of our experiment is to relate NMR relaxations to the B-2p Fermi-level DOS of transition metal diborides.…”

Low electron density of states at the boron site of TMB2 (TM = Ti, Zr, Hf, and Nb): a 11B NMR study

“…Besides, the resonance (Knight) shift and the electric field gradient (EFG) are related to the electronic environment of the resonating nucleus. Except of the HfB 2 the EFGs at the boron site have been measured in all present diborides [3] and the theoretical interpretation have been given by Schwartz et al [4] and Medevedeva et al [5].…”

Difference in the outermost layer betweenTaB2(0001)andHfBYamamoto1, Kobayashi2, Kawanowa3 et al. 1999Phys. Rev. B4312261View full textAdd to dashboardCite

“…[3][4][5][6][7] These are layered compounds with a hexagonal AlB 2 -type structure in which a graphitelike boron layer alternates with a close-packed metal layer. 8 Under room temperature and atmospheric pressure crystalline boron in the form of graphite does not exist.…”