The phonon dispersion curves and the phonon density of states of ${\mathrm{Mo}}_3$Si have been measured by inelastic neutron spectroscopy. In spite of the low $T_c$ of this compound ($T_c$=1.2 K), pronounced electron-phonon coupling effects have been found in some optic branches. The observed features are surprisingly similar to phonon anomalies which previously have been found in the high-$T_c$ A15 compound ${\mathrm{Nb}}_3$Sn, but not in low-$T_c$ compounds ${\mathrm{Nb}}_3$Sb. Apart from the anomalous phonons, which contribute only little to the phonon density of states, the phonon frequencies are rather high. The results have been analyzed with a Born–von Kármán model including axially symmetric forces up to the eighth nearest neighbors. The failure of this model to reproduce the phonon anomalies was overcome by introducing the coupling of an electronic shell around the Mo atoms to the core and to neighboring shells as additional parameters. Selected phonon frequencies have been determined at low temperatures. Upon cooling, a slight increase of the phonon frequencies has been observed for normal as well as for anomalous phonons. Moreover, the width of the phonon groups has been, in all cases, resolution limited.

• Received 3 March 1986

DOI:https://doi.org/10.1103/PhysRevB.34.2751