Actinide chalcogenides and pnictides. III. Optical-phonon frequency determination in UX and ThX compounds by neutron scattering

Abstract

For pt. II see abstr. A44356 of 1973. The optical-phonon branch in actinide compounds is flat provided there is both a large mass difference between the actinide ion and the lighter anion and negligible interaction between neighbouring anions. For such a compound the neutron time-of-flight spectrum using a polycrystalline sample will give a sharp peak at the optical frequency. This concept is used here in measuring the mean optical frequency for nine AnX compounds with the rock-salt structure where An=U and Th and X=C, N, P, S and Se. The optical frequency is interpreted in terms of a single nearest-neighbour An-X force constant. It is found that the U-X force constants are 20-30% higher than the corresponding Th-X force constants. In both cases the constants increase with the An-X separation. UC and ThC have anomalously low force constants.