On optical phonons and elasticity in the hcp transition metals Fe, Ru and Re at high pressure

The frequencies of the transverse-optical Gamma -point phonon were determined for the hexagonal transition metals Fe, Ru and Re by high-pressure Raman spectroscopy up to 60 GPa. Comparison is made with available theoretical frequency-data. The elastic shear constants C-44, determined from the Raman frequencies, are consistent with ultrasonic low-pressure data and theoretical high-pressure data and do not support the high-pressure data obtained from lattice-strain experiments.