Abstract
A crystalline-to-crystalline phase transformation, including chemical decomposition, has been observed in SnO2 nanopowder irradiated by 2.2GeV 197Au ions. X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) were used to characterize the transformation from tetragonal SnO2 (P42/mnm) to tetragonal SnO (P4/nmm), with trace quantities of β-Sn (I41/amd). At a fluence of approximately 2.0×1012ions/cm2, 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 2.4×1013ions/cm2. 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.
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