High-Temperature Superconductivity In The Ti-H System At High Pressures

Search for stable high-pressure compounds in the Ti-H system reveals the existence of titanium hydrides with new stoichiometries, including Ibam-Ti2H5, I4/m-Ti5H13, I (4) over bar -Ti5H14, Fddd-TiH4, Immm-Ti2H13, P (1) over bar -TiH12, and C2/m-TiH22. Our calculations predict I4/mmm -> R (3) over barm and I4/mmm -> Cmma transitions in TiH and TiH2, respectively. Phonons and the electron-phonon coupling in all searched titanium hydrides are analyzed at high pressure. It is found that Immm-Ti2H13, rather than the hydrogen-richest C2/m-TiH22, exhibits the highest superconducting critical temperature T-c. The estimated T-c of Immm-Ti2H13 and C2/m-TiH22 are, respectively, 127.4-149.4 K (mu* = 0.1-0.15) at 350 GPa and 91.3-110.2 K at 250 GPa, as found by numerically solving the Eliashberg equations.