Raman scattering by phonons and crystal-field excitations in cerium hydrides

The effect of cerium hydrides (deutrides) stoichiometry, CeH(D)2+x (x = 0–0.90), on the vibrational and Ce+3 crystal-field excitations was studied at room temperature by means of Raman scattering spectroscopy. The assignment of CeH2+x vibrational Raman bands, with x < 0.6, are facilitated by the remarkable similarity of their frequencies to the previously measured inelastic neutron scattering (INS) frequencies for the corresponding LaH2+x. Above x≈0.60 the INS and Raman spectra become increasingly different presumably due to the repulsive H–H interactions, which are also known to increase the magnitude of dispersion in optic-mode vibrations. The intensity of a band at ∼810 cm−1 relative to that of a band at ∼710 cm−1 decreases by an order of magnitude from x≈0.60 to x≈0.72 and remain practically constant up to x = 0.90. Since at room temperature the composition dependent structural tetragonal-cubic and electronic metal-semiconductor transitions occur at x≈0.60 and 0.7 < x < 0.8, respectively, the above spectral changes cannot be clearly assigned to either.