抄録
Starting from a viewpoint that melting phenomena are caused by an instability of the lattice vibrations, neutron scattering studies were made on NaF to see how the anharmonic interaction of phonons develops with increasing temperature. The phonon frequency shift and the damping of the [110] TA1 mode were measured as functions of wave number and frequency over a wide range of temperature from 300 to 1250 K. At temperatures very close to the melting point Tm=1266 K, high ω(q) phonons are heavily damped, but low ω(q) phonons are still surprisingly stable. A marked frequency softening was observed only for this mode; no evidence for premelting phenomena could be seen, and Tm appears quite suddenly. It is argued that Tm will be determined not by the bulk but by the surface potential.
