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 omega decreases whereas the damping gamma increases with increasing temperature and decreasing particle size. Near the Curie temperature in the NPs there appears a kink in omega(T) and gamma(T). The phonon properties are very sensitive especially to the enharmonic spin-phonon interaction. In dependence of the radius of the doping ions compared to the host ones omega 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 enharmonic 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.