| Abstrakt: |
Divalent tin fluorides and chloride fluorides appear to be stable relative to oxidation to tetravalent tin at ambient temperature. X-ray diffraction shows only the line of the tin(II) compound, however the 119Sn Mössbauer spectrum of all tin(II) polycrystalline samples has a small broad peak at ca. 0 mm/s. This is the case of polycrystalline α −SnF2, while the spectrum of a large single crystal polished sufficiently thin shows only the tin(II) doublet, with no SnO2 peak at 0 mm/s. This shows that there is surface oxidation of each solid particle, to give a thin amorphous layer of SnO2 stannic oxide. However, the Mössbauer peak of SnO2 does not grow with prolonged exposure to air at ambient temperature, therefore it must be assumed that the layer of SnO2 has a passivating effect, however oxidation increases at higher temperatures. We have investigated in this work the passivating effect of a layer of SnO2 in two types of solid solutions: (i) in the fluorite type M1−xSnxF2, where the amount of tin at low x values is not sufficient to provide full coverage of the surface of the particles, and (ii) in the PbClF type doubly disordered solid solution, Ba1−xSnxCl1+yF1−y. It was found that passivation works well in the M1−xSnxF2 solid solution, however most of the time, it does not work so well for Ba1−xSnxCl1+yF1−y where it is strongly dependent on the method of preparation and the bonding strength, as shown by the variation versus the tin(II) recoil-free fraction. [ABSTRACT FROM AUTHOR] |
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