Mössbauer Spectrometry

Mössbauer spectrometry gives electronic, magnetic, and structural information from within materials. A Mössbauer spectrum is an intensity of γ-ray absorption versus energy for a specific resonant nucleus such as Fe or Sn. For one nucleus to emit a γ-ray and a second nucleus to absorb it with efficiency, both nuclei must be embedded in solids, a phenomenon known as the “Mössbauer effect.” Mössbauer spectrometry looks at materials from the “inside out,” where “inside” refers to the resonant nucleus. Mössbauer spectra give quantitative information on “hyperfine interactions,” which are small energies from the interaction between the nucleus and its neighboring electrons. The three hyperfine interactions originate from the electron density at the nucleus (the isomer shift), the gradient of the electric field (the nuclear quadrupole splitting), and the unpaired electron density at the nucleus (the hyperfine magnetic field). Over the years, methods have been refined for using these three hyperfine interactions to determine valence and spin at the resonant atom. Even when the hyperfine interactions are not easily interpreted, they can often be used reliably as “fingerprints” to identify the different local chemical environments of the resonant atom, usually with a good estimate of their fractional abundances. Mössbauer spectrometry is useful for quantitative phase analyses or determinations of the concentrations of resonant element in different phases, even when the phases are nanostructured or