The ionization of PCl6− in the solid state under pressure. I. Phase diagram of phosphorus pentachloride

It is suggested that the PCl6− ion should ionize to PCl4+ and 2Cl− in the solid under pressure, and evidence has been sought by measuring the phase diagram of phosphorus pentachloride, which has the constitution PCl4+PCl6−. Two new phases were discovered, one of which is wholly metastable relative to the ordinary phase.