  The structural, superconducting, and electronic phase diagram of
[Tl4]Tl1-xSnxTe3 is reported. Magnetization and specific heat measurements show
bulk superconductivity exists for 0 < x < 0.4. Resistivity measurements
indicate a crossover from a metallic state for low dopings to a doped insulator
at x = 1. Universally, there is a large non-Debye specific heat contribution,
characterized by an Einstein temperature of {\theta}E ~ 35 K. Density
functional theory calculations predict x = 0 to be a topological metal, while x
= 1 is a topological crystalline insulator. The disappearance of
superconductivity correlates with the transition between these distinct
topological states.
