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

The local density of states at the boron site in TMB2 (TM=Ti, Zr, Hf, and Nb) has been examined using the solid-state 11B NMR technique. The magic angle spinning (MAS) NMR spectra at room temperature and the spin-lattice relaxation rates have been measured as functions of temperature (30-293 K). The resonance line shifts are small and become more negative in the direction from 3d- to 5d-elements. The relaxation rates follow a linear law characteristic of hyperfine magnetic interaction with conduction electrons. With borides of IV group metals the data can be understood in terms of a very low s-electron density of states and absence of a p-character of the conduction electron wave function at the Fermi level while in the case of NbB2 a small partial p-electron density of states is assumed. Then, the results are in good agreement with the earlier theoretical prediction