Limits of Sensitivity of Mössbauer Spectrometry
  
    57Fe Mössbauer spectrometry was carefully applied to Na3Fe2(PO4)2F3, a fluorophosphate crystalline ferric compound. Two structural phase transitions involving very slight motions of Na+ cations were evidenced from the temperature dependence of the quadrupolar splitting (see left figure and note the scale!), in agreement with those observed in isotypic compounds, either by diffraction technique or by calorimetric measurement. Right figure exhibits the different phases involving small structural changes. Consequently, it is important to emphasise the extremely high neighbouring sensitivity of 57Fe Mössbauer spectrometry.