Synthesis of superconducting phase of La 0.5 Ce 0.5 H 10 at high pressures.

Clathrate hydride Fm3̄m -LaH 10 has been proven as the most extraordinary superconductor with the critical temperature T c above 250 K upon compression of hundreds of GPa in recent years. A general hope is to reduce the stabilization pressure and maintain the high T c value of the specific phase in LaH 10 . However, strong structural instability distorts Fm3̄m structure and leads to a rapid decrease of T c at low pressures. Here, we investigate the phase stability and superconducting behaviors of Fm3̄m -LaH 10 with enhanced chemical pre-compression through partly replacing La by Ce atoms from both experiments and calculations. For explicitly characterizing the synthesized hydride, we choose lanthanum-cerium alloy with stoichiometry composition of 1:1. X-ray diffraction and Raman scattering measurements reveal the stabilization of Fm3̄m -La 0.5 Ce 0.5 H 10 in the pressure range of 140-160 GPa. Superconductivity with Tc of 175±2 K at 155 GPa is confirmed with the observation of the zero-resistivity state and supported by the theoretical calculations. These findings provide applicability in the future explorations for a large variety of hydrogen-rich hydrides.&#xD.