Phase transformation and chemical decomposition of nanocrystalline SnO2 under heavy ion irradiation

A crystalline-to-crystalline phase transformation, including chemical decomposition, has been observed in SnO2 nanopowder irradiated by 2.2 GeV Au-197 ions. X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) were used to characterize the transformation from tetragonal SnO2 (P4(2)/mnm) to tetragonal SnO (P4/nmm), with trace quantities of beta-Sn (14(1)/amd). At a fluence of approximately 2.0 x 10(12) ions/cm(2), diffraction maxima corresponding to SnO became clearly evident and increased in intensity as fluence increased. The proportion of SnO, as determined by Rietveld refinement of XRD data, reached 23.1 +/- 0.8% at the maximum fluence investigated of 2.4 x 10(13) ions/cm(2). Raman spectra show high photoluminescence (PL) intensity before and during initial SnO formation, indicating the importance of oxygen vacancies in the transformation process. Small-angle X-ray scattering (SAXS) analysis provided evidence of ion tracks, but no tracks were observed using high-resolution TEM (HRTEM). The transformation likely occurs through a multiple-impact mechanism, based on the accumulation of O vacancies, defect ordering, and partially localized Sn reduction. (C) 2017 Elsevier B.V. All rights reserved.