Abstract
We report the results of a nuclear magnetic resonance (NMR) study of near the ordered composition with at temperatures between 4 and 500 K. All compositions are found to be metallic or semimetallic, though electrical resistivity has indicated a metal-insulator transition at The low-temperature NMR relaxation rates for stoichiometric and nonstoichiometric and compounds follow a Korringa law, associated with a finite density of carriers at the Fermi level. High-temperature relaxation rates for go over to a semiconductorlike activated form, providing information about the gap structure near the Fermi energy. The results are consistent with pseudogap features identified by recent band-structure calculations, although with smaller energy splittings. We analyze pseudogap changes vs composition, and compare the band-filling behavior to a recent coherent potential approximation calculation.
- Received 12 November 1999
DOI:https://doi.org/10.1103/PhysRevB.61.9863
©2000 American Physical Society