> Whereas the magnetic susceptibility includes a small ferromagnetic component (likely due to local magnetic order in the inhomogeneous network of Cu substituents), the magnetic susceptibility exhibits no anomalies indicative of phase transitions (including superconductivity) in a wide range of temperatures up to 800 K. We discuss possible origins of the anomalies reported in phase-impure powder samples. In particular, the impurity phase Cu₂S exhibits two structural phase transitions, with the one at 398 K coinciding with an insulator-to-metal transition that may be mistakenly attributed to superconductivity.