Nanocrystalline SnO2 and SiO2- doped SnO2 samples prepared by the Sol- gel process have been investigated by X- ray diffraction and positron lifetime spectroscopy. lt was shown that only two kinds of defects were found in the interfaces of both samples

i.e.free volumes and microvoids. lt appeared that when the sintering temperature was lower than the crystallization temperature

the grains grew slowly

and above this temperature the growth became faster. Furthermore

grain growth of the pressurized samples was slower than that of the powder. And SiO2 doping effectively restrained the growth of nanocrystalline SnO2 grains