LATTICE DYNAMICS OF NIOBIUM .2. KOHN ANOMALIES IN NIOBIUM

The sources of the discrepancies between the experimentally determined phonon frequencies in niobium and the predictions of tensor force-constant models have been investigated. In the regions of reciprocal space where the phonon dispersion is small, the discrepancies are thought to be due to systematic resolution errors. In the rest of reciprocal space, the discrepancies are interpreted in terms of Kohn anomalies, and the shape of portions of the Fermi surface deduced. Of three forms for the Fermi surface in niobium suggested by Mattheiss, the form W2, corresponding to a width (Γ25′H25′) of 0·55 rydbergs for the d bands in niobium, is found to agree best with this interpretation.