Pressure and temperature dependence of hyperfine field parameters of iron and its compounds by Synchrotron Mössbauer Spectroscopy*

The pressure and temperature dependence of the hyperfine interaction parameters like internal hyperfine magnetic field, isomer shift, and quadrupole splitting have been measured with high precision using a pulsed synchrotron radiation source. The pressure range varied between ambient to 30 GPa, and the temperature range between 10 to 600 K. Taking advantge of a special "hybrid" filling mode of the Advanced Photon Source, we observed the nuclear decay of pure iron and several compounds over 6 lifetimes, reaching an accuracy of better than 0.1%. Relative isomer shift between bcc-iron and hcp iron is also measured with high precision, provining a direct measure of s-electron density at the iron nucleus due to phase change.