The flourishing metal clathrate superhydrides is a class of recently discovered materials that possess record breaking near-room-temperature superconductivity at high pressures, because hydrogen atoms behave similarly to the atomic metallic hydrogen. While series of rare-earth clathrate superhydrides have been realized, the superconductivity of the first proposed clathrate calcium superhydride that initiates this major discovery has not been observed yet and remains of fundamental interest in the field of high-pressure physics. Here, we report the synthesis of calcium superhydrides from calcium and ammonia borane precursors with a maximum superconducting temperature of 215 K at 172 GPa, confirmed by the observation of zero resistance through four-probe electrical transport measurements. An exceedingly high upper critical magnetic field was estimated to be 203 T at zero temperature in the WHH model. Inferred from the synchrotron X-ray diffraction, together with the consistency of superconducting transition temperature and equation of states between experiment and theory, sodalite-like clathrate CaH6 is one of the best candidates for this high-Tc CaHx.
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