Electrolyte properties of and were studied using single crystals, pressed pellets, and thin films. Ionic conductivity and heat of movement of mobile species were determined for both forms of lead fluoride. In addition, the electronic conductivity and transport number for the cubic were determined. Converison of to was studied by differential thermal analysis, with an observed transition temperature in the range 334°–344° Partial reconversion of back to was effected by pressing the material at pressures above 30,000 psi. A voltage of 1.7 mV ( positive) generated between pellets of and separated by a salt bridge implied that the is the more stable form at room temperature and atmospheric pressure.