Hydrogen bond conversion and near room temperature superconductivity in oxygen hydrides

The discovery of hydrogen-rich high ${T}_{c}$ superconducting materials, such as ${\mathrm{H}}_{3}\mathrm{S}$ and ${\mathrm{LaH}}_{10}$ under the ultrahigh pressures of more than one million atmospheres is constantly refreshing the record of superconducting critical temperature, ushering the era of room temperature superconductivity. Herein, we investigate the role of the hydrogen bond in the superconductivity of the superhydrides of oxygen, as the hydrogen bond reflects an electronic structure of oxygen in terms of the polarity of the lone pair of electrons. In an extensive exploration of the structures and superconductivity in oxygen hydrides, we predict a high ${T}_{c}$ superconducting transition in $Im\text{\ensuremath{-}}3m$ phase of ${\mathrm{H}}_{3}\mathrm{O}$ with first-principles calculations combined with swarm-structure search. A high ${T}_{c}$ of 301.5 K is obtained, as the $Im\text{\ensuremath{-}}3m$ phase of ${\mathrm{H}}_{3}\mathrm{O}$ is dynamically stabilized at the pressure as high as 670 GPa. It is found that a significant contribution to superconduction arises from the oxygen $s$-state electrons. With increasing the pressure, the orbital hybridization brings the essential rise of the coordination unsaturation that is favorable for the emergence of the superconductivity, whereas the superhydride compound reaches the stability at a much higher pressure than that for the isoelectric compounds of the sulfur, selenium, and tellurium due to the difficulty in orbital hybridization for the larger energy-level spacing in oxygen. Considering the difference in the hydrogen bond, we also investigate the isotope effect and obtain ${T}_{c}$ values up to 247 K for ${\mathrm{D}}_{3}\mathrm{O}$. Our work deepens the understanding of the relationship between superconductivity and coordination unsaturation in the presence of the strong hydrogen bond and can be instructive for the design of superconducting materials under pressurization.