Microstructure and transport properties of ceria and samaria doped ceria thin films prepared by EBE–IBAD

Ceria and samaria doped ceria thin films were prepared by ion beam assisted electron beam evaporation. Two substrate temperatures were used (200 and 500 °C), together with ion assistance, as preparation parameters to obtain thin films with controlled microstructure. The samaria doped ceria films were grown using a multilayer strategy, alternating deposition of ceria and samaria layers. X-ray diffraction and scanning electron microscopy were used to characterise the evolution of the structure and microstructure of the films. The electrical conductivity of the thin films was studied in pure O2 atmosphere as a function of temperature by two point dc measurements. The transport characteristics of the films (activation energy and conductivity) exhibited clear grain size dependence. The importance of both ionic and electronic contributions to the total conductivity was identified. In particular, the highest electrical conductivity was achieved for ceria samples prepared at 200 °C under Ar+ assistance. These samples had the smallest grain size (∼ 20 nm). Samaria doped ceria films showed the highest conductivity and activation energies consistent with ionic charge transport when they were prepared at 500 °C under Ar+ bombardment and doped with 35 wt.% of Sm2O3.