SIMS analysis using O-18(2) gas was applied to investigate the effects of oxygen diffusion from the atmosphere on thermal properties of a float glass. It was revealed that a phase separation was induced by the oxygen diffusion, resulting in degradation of the optical properties of the glass. The same analysis was performed for fluorine-doped SnO2 films grown by atmospheric chemical vapor deposition (APCVD). It was found that the amount of diffused O-18 into the film was larger for the film with lower resistivity when the films were heat-treated in O-18(2)/N-2 atmosphere. Based on the results obtained, the roles of oxygen in the electrical properties of the films are discussed. (C) 2004 Elsevier B.V All rights reserved.