  Various tin hydrides SnHx (x = 4, 8, 12, 14) have been theoretically
predicted to be stable at high pressures and to show high-critical-temperature
superconductivity with Tc ranging from about 70 to 100 K. However, experimental
verifications for any of these phases are still lacking to date. Here, we
report on the in-situ synthesis, electrical resistance, and synchrotron x-ray
diffraction measurements of SnHx at ~ 200 GPa. The main phase of the obtained
sample can be indexed with the monoclinic C2/m SnH12 via comparison with the
theoretical structural modes. A sudden drop of resistance and the systematic
downward shift under external magnetic fields signals the occurrence of
superconductivity in SnHx at Tc = ~ 70 K with an upper critical field u0Hc2(0)
= ~ 11.2 T, which is relatively low in comparison with other reported high-Tc
superhydrides. Various characteristic superconducting parameters are estimated
based on the BCS theory.
