Characteristic Temperatures of the Mössbauer Fraction and Thermal-Shift Measurements in Iron and Iron Salts

Abstract

M\"ossbauer spectra have been measured in metallic iron, sodium nitroprusside, sodium ferrocyanide, and potassium ferrocyanide absorbers between 78 and 293 \ifmmode^\circ\else\textdegree\fi{}K. The temperature dependences of the M\"ossbauer fraction ${f}_{a}$ and the resonant velocity ${V}_{0}$ were fitted to Einstein and Debye lattice-vibration models. The characteristic temperatures of the models fitted to ${f}_{a}$ are consistently lower than those fitted to ${V}_{0}$, showing the sensitivity of ${f}_{a}$ to low-frequency modes of vibration. The characteristic temperatures obtained from ${V}_{0}$ are higher for the salts than for the metal, indicating the presence of higher-frequency modes in the salts. This interpretation is verified semiquantitatively by comparing the thermal-shift Debye temperatures of the salts to their infrared absorption frequencies. The M\"ossbauer fraction of potassium ferrocyanide shows a weaker temperature dependence than expected for a harmonic solid which suggests potassium ferrocyanide is anharmonic in the temperature range studied.