Neutron diffraction search for the charge density waves in early rare earth metal deuterides RD3 (R = La, Ce)

The results of neutron diffraction measurements performed on CeDsub(x) near the trihydride composition MeD3 at room temperature and on LaDsub(2.9) at liquid nitrogen and room temperatures are presented. Superstructure reflections have been found. The system of additional reflections in lanthanum deuteride is different from that in cerium deuteride. The concentration and temperature boundaries for the transformed phases are reported. The experimental results are discussed on the basis of Kulikov's excitonic dielectric model for metal-to-semiconductor phase transitions. The determination of crystal structures from experimental neutron diffraction patterns is discussed. (Auth.)