Chemical and structural modifications occurring in yttria stabilized zirconia and magnesium aluminate spinel single crystals submitted to Cs ion-implantation and thermal treatments are investigated by RBS/C experiments. Changes of the sample composition, damage created in the crystals and behavior of implanted ions are studied as a function of the Cs fluence and annealing temperature. Variations of the stoichiometry, decrease of the lattice disorder and diffusion of implanted species are observed above 700–800 °C with marked differences for both materials.mechanism is proposed.