paper

High-Temperature Superconductivity in the Ti--H System at High Pressures

arXiv:1911.09293 · doi:10.1103/PhysRevB.101.134108

Abstract

Search for stable high-pressure compounds in the Ti--H system reveals the existence of titanium hydrides with new stoichiometries, including Ibam-Ti $_{2}$ H $_{5}$ , I4/m-Ti $_{5}$ H $_{13}$ , I $4 ˉ$ -Ti $_{5}$ H $_{14}$ , Fddd-TiH $_{4}$ , Immm-Ti $_{2}$ H $_{13}$ , P $1 ˉ$ -TiH $_{12}$ , and C2/m-TiH $_{22}$ . Our calculations predict I4/mmm $\to$ R $3 ˉ$ m and I4/mmm $\to$ Cmma transitions in TiH and TiH $_{2}$ , respectively. Phonons and the electron--phonon coupling of all searched titanium hydrides are analyzed at high pressure. It is found that Immm-Ti $_{2}$ H $_{13}$ rather than the highest hydrogen content C2/m-TiH $_{22}$ , exhibits the highest superconducting critical temperature T $_{c}$ . The estimated T $_{c}$ of Immm-Ti $_{2}$ H $_{13}$ and C2/m-TiH $_{22}$ are respectively 127.4--149.4 K ( $I^¼^{*}$ =0.1-0.15) at 350 GPa and 91.3--110.2 K at 250 GPa by numerically solving the Eliashberg equations. One of the effects of pressure on T $_{c}$ can be attributed to the softening and hardening of phonons with increasing pressure.