A Mossbauer study of lattice dynamics in iron and iron salts



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Mossbauer spectra have been measured in metallic iron, sodium nitroprusside, sodium ferrocyanide, and potassium ferrocyanide absorbers at several temperatures between 78°K and 293°K. The Mossbauer fraction f[lowered a] and resonant velocity V[lowered o] in each spectrum were determined. The observed temperature dependences of f[lowered a] and V[lowered o] in each absorber were fitted to both Einstein and Debye lattice vibration models. The characteristic temperatures of the models fitted to f[lowered a] are consistently lower than those fitted to V[lowered o], showing the sensitivity of the Mossbauer fraction to low-frequency modes of vibration. The characteristic temperatures obtained from V[lowered o] are higher for the salts than for the metal, indicating the presence of higher-frequency modes of vibration in the salts. This interpretation is verified semi-quantitatively by comparing the thermal-shift Debye temperatures of the salts to their infrared absorption frequencies. The Mossbauer fraction of potassium ferrocyanide shows a weaker temperature dependence than expected for a harmonic solid. This suggests that potassium ferrocyanide is anharmonic in the temperature range studied. The magnetic field at the Fe[raised 57] nucleus in metallic Fe and the quadrupole splitting in sodium nitroprusside were each measured as a function of temperature. These measurements compare well with results of previous studies.