Thermal stability of Ce0.5Gd0.5O1.75 nanoparticles in contact with an amorphous SiO2

Abstract

Morphology, microstructure and phase evolution of nanocrystalline Ce0.5Gd0.5O1.75 mixed oxide supported on amorphous SiO2 were studied in oxidizing and reducing atmosphere by XRD, TEM and SEM-EDS. The Ce0.5Gd0.5O1.75/SiO2 samples were prepared by two methods: impregnation of the support with an aqueous solution of nitrates and deposition of homogeneous Ce0.5Gd0.5O1.75 nanoparticles synthesized using the microemulsion method. The latter system is structurally and chemically stable in the oxidizing atmosphere up to 1000°C, exhibiting only a small increase of the mean crystallite size of the mixed oxide from 2 to 3nm. Prolonged heating at 1100°C for 24h caused partial decomposition of the mixed oxide and formation of small amount of B-Gd2Si2O7. In the reducing atmosphere the Ce0.5Gd0.5O1.75 underwent amorphization and spreading over SiO2 already at 900°C to form an amorphous silicate. Most of the silicate remained amorphous even after reduction at 1100°C, but certain amount crystallized into particles with strongly defected structure. The system prepared by impregnation exhibited significantly worse thermal stability due to chemical inhomogeneity. The complex systems synthesized in this work, containing nanocrystalline particles of mixed silicate with high concentration of Ce3+ ions, may be interesting as scintillating materials.