Lattice Dynamics in Covalent Solids: Sn in Sns2_Xsex (0≤X≤2)

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Mössbauer effect studies using the 23.8 keV gamma transition in 119Sn have been carried out on the system SnS2-xSe x (O≤x≤2) on both microcrystalline powders and single crystal samples. The composition dependence of the isomer shift parameter for the single line resonance spectrum shows that the covalency increases as x increases; the 5s electron population of tin in SnSe2 is ∼0.13 greater than it is in SnS2. From the temperature dependence of the area under the resonance curve it is possible to extract a Mössbauer lattice temperature θM which is only weakly dependent on composition for samples prepared in an identical manner. Single crystal orientation experiments with SnS2 and SnSe2 have been carried out at 295 ± 1 K to investigate the anisotropy in the metal atom motion parallel and perpendicular to the crystallographic c axis (perpendicular and parallel to the easy cleavage plane). The vibrational anisotropy ratio, 〈x ∥〉/〈x⊥〉 is found to be 2.25 in SnS2 and 1.58 in SnSe2 at room temperature. The absolute values of the tin atom vibrational amplitudes have been calculated using the recoil-free fraction data for metallic (β) tin under identical conditions.

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