We report the normal-state and superconducting properties of the silver-oxide clathrate Ag6O8AgNO3. Electrical resistivity, specific heat, and DC and AC susceptibility measurements as functions of magnetic field and temperature show phase transitions near 90 and 185 K. We find that Ag6O8AgNO3 is a bulk superconductor with the superconducting transition temperature Tc = 1.04 K. We observe a clear kink structure in the field dependence of the real part of AC susceptibility, suggesting a change in vortex state. Furthermore, we present the H-T phase diagram of this compound and estimate the upper critical field Hc2(0) to be about 770 Oe. We also discuss the superconducting properties in a Ginzburg-Landau framework.
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