Crystal structures and superconductivity of technetium hydrides under pressure.

Guided by a simple strategy in search of new superconducting materials, we have performed extensive simulations on crystal structures and electronic properties of Tc-H compounds at high pressures. Three stoichiometries, namely TcH, TcH, and TcH, were predicted to be stable under high pressure. The chemical bonding characters of Tc-H compounds were investigated by introducing the electron localization function and electronic projected density of states, which show that the stable Tc-H compounds including TcH, TcH and TcH are all classified as ionic crystals as a result of Tc → H charge transfer. Based on the Bardeen-Cooper-Schrieffer theory and estimated from the Allen-Dynes modified McMillan equation, the superconducting critical temperature (T) values of the I4/mmm phase for TcH are 5 K at 100 GPa and 11 K at 200 GPa. Moreover, it is found that Cmcm-TcH and P4/mmc-TcH at 300 GPa have T values of 9 K and 10 K, respectively. Our current results significantly enrich the crystal structures of the Tc-H system and provide a further understanding of their structural features and physical properties.