Micro-pellet method for infrared absorption spectroscopy using a diamond anvil cell under a quasi-hydrostatic condition

Abstract

A method was proposed for measuring infrared absorption spectra at high pressure under quasi-hydrostatic pressure conditions. Two KBr micro-pellets were prepared as samples, and reference materials were charged in a diamond anvil cell, applying helium as the pressure-transmitting medium. Using this method, the quasi-hydrostatic pressure condition was retained up to approximately 20 GPa. Furthermore, hydrostaticity was much better than conventional pressure-transmitting media used for infrared spectroscopy. Infrared absorption spectra of α -FeOOH at high pressure were measured using the KBr micro-pellet method with a helium pressure-transmitting medium. Downshift of the OH stretching vibration was observed with increasing pressure. Use of the KBr micro-pellet method for infrared absorption spectroscopy at high pressure is a complementary experimental technique to neutron diffraction at high pressure for studying the pressure response of hydrogen bonds.

Keywords:

• infrared spectroscopy
• pressure-transmitting medium
• hydrostatic condition
• hydrogen bonds

Acknowledgements

This study was financially supported by a grant-in-aid for Creative Scientific Research (19GS0205) from the Japan Society for the Promotion of Science.