High-pressure crystal structure studies of Fe, Ru and Os Original Research Article

In order to reveal structural trends with increasing pressure in d transition metals, we performed full potential linear muffin-tin orbital calculations for Fe, Ru, and Os in the hexagonal close packed structure. The calculations cover a wide volume range and demonstrate that all these hexagonal close-packed metals have non-ideal c/a at low pressures which, however, increases with pressure and asymptotically approaches the ideal value at very high compressions. These results are in accordance with most recent experiment for Ru and Os. The experimental data for iron is not conclusive, but it is believed that the c/a ratio decreases weakly with increasing pressure at moderate compression. Since, the experimental and calculated equations of state for iron are in increasingly good agreement with increasing pressure, it is possible that either the negative c/a trend is valid only for a restricted pressure range, or related to the experimental difficulties (e.g. non-hydrostaticity).