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

TL;DR

This study predicts new titanium hydrides with high-pressure stability and analyzes their superconducting properties, identifying Immm-Ti$_2$H$_{13}$ as having the highest T$_{c}$ around 127-149 K at 350 GPa.

Contribution

The paper reports the discovery of new stable titanium hydrides with novel stoichiometries and provides detailed predictions of their superconducting critical temperatures under high pressure.

Findings

Immm-Ti$_2$H$_{13}$ exhibits the highest T$_{c}$ among studied hydrides.

Predicted T$_{c}$ for Immm-Ti$_2$H$_{13}$ is 127.4--149.4 K at 350 GPa.

Pressure influences T$_{c}$ through phonon softening and hardening.

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$\bar{4}$-Ti$_5$H$_{14}$, Fddd-TiH$_4$, Immm-Ti$_2$H$_{13}$, P$\bar{1}$-TiH$_{12}$, and C2/m-TiH$_{22}$. Our calculations predict I4/mmm $\rightarrow$ R$\bar{3}$m and I4/mmm $\rightarrow$ 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 ($\mu^{*}$=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.