A Mossbauer study of lattice dynamics in iron and iron salts

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.