Mössbauer spectroscopy methodology at the cutting-edge of high-pressure research

This paper provides a concise, introductory review intended mainly for Mössbauer spectroscopy (MS) scientists not familiar with the most modern aspects of High Pressure (HP) methodology. Following a short introduction to the 1^st generation HP-MS based on Drickamer's pressure cells, we describe the principles of the 2^nd generation of HP-MS based on the Diamond Anvil Cell (DAC) including in-situ pressure measurements, the use of the high-specific activity ⁵⁷Co(Rh) point sources, and examples of miniature DAC's. Finally, we present recent studies carried out with ⁵⁷Fe HP-MS combined with other HP techniques such as resistivity, and synchrotron-based x-ray diffraction, describing unique cases of the breakdown of magnetism and the Mott transition in hematite (Fe₂O₃), pressure-induced spin crossover in Wüstite (FeO), pressure induced Fe ²⁺ → Fe³⁺ in Fe(OH)₂, and (P,T) induced inverse↔ normal spinel transition in magnetite (Fe₃O ₄).