Phonon measurements in uranium monosulphide

Abstract

The phonon dispersion relations have been measured for the (00 zeta ), ( zeta zeta 0) and ( zeta zeta zeta ) directions for uranium sulphide at 300K by neutron inelastic scattering. In the ( zeta zeta zeta ) direction the LA and TA branches are nearly degenerate in frequency and in the ( zeta zeta 0) direction the LA and TA2 branches are also nearly degenerate. The optical branches exhibit little dispersion. Neither the rigid-ion nor the shell model is capable of giving a satisfactory description of the lattice vibrations. The high-frequency compressional sound velocities are found to be lower than those determined at low frequencies by ultrasound, whereas the high-frequency shear velocities are higher.