Crystal structures and high-temperature superconductivity in molybdenum-hydrogen binary system under high pressure

Motivated by advances in hydrogen -rich superconductors in the past decades, we conducted variablecomposition structural searches in Mo-H binary system at high pressures. A new composition -pressure phase diagram of thermodynamically stable structures has been derived. Besides all previously discovered superconducting molybdenum hydrides, we also identified series of thermodynamically metastable superconducting structures, including I4/mmm-Mo3H14, I4cm-MoH9, P4/nmm-MoH10 and P4212-MoH10, with the superconducting transition temperatures from 55 to 126 K. In these superconducting molybdenum hydrides, vibrations from the Mo-atoms contributes significantly to the electron-phonon coupling and the superconducting transition temperature, in complementary to the contributions by the vibrations of the H -atoms. Our works highlight compounds with non -integer composition ratio and metastable states could be of importance in material searches for example the potential high temperature superconductors.