Theoretical study of the phonon properties of pure and ion doped CeO2 nanoparticles

Using a microscopic model taking into account the spin-phonon interactions we have studied the phonon properties of pure and ion doped CeO2 nanoparticles (NPs). The phonon energy ω decreases whereas the damping γ increases with increasing temperature and decreasing particle size. Near the Curie temperature in the NPs there appears a kink in ω(T) and γ(T). The phonon properties are very sensitive especially to the anharmonic spin-phonon interaction. In dependence of the radius of the doping ions compared to the host ones ω could be reduced (Pr,Sm,Nd,La) or enhanced (Co,Y,Cu). The changes of the lattice parameters lead to changes of the exchange interaction and anharmonic spin-phonon interaction constants. The phonon damping is always enhanced by the doped NPs. It is shown that the changes in the phonon energy and damping of ion doped CeO2 NPs are due to combined effects of size, strain or defect effects.