Stable and Metastable Phase Equilibria in the Liquid-State and Solid-State PbO-GeO2 System

A literature review on phase equilibria in the PbO-GeO2 system is reported and the main sources of discrepancies in the results of different authors are considered. Uncontrolled metastable phase formation is shown to be the most probable cause for disagreements about composition and structures of phases formed in the system. The authors' results of investigations of physicochemical properties for stable and metastable phases obtained by various routes, including mechanochemical and thermal (crystallization of a metastable melt) activation, are presented. Similar phenomena are shown to take place in the binary PbO-SiO2 system and under partial substitution Ge Si in the ternary oxide system PbO-GeO2-SiO2. The particular role played by the 6s(2) electron pair a Pb2+ ion in stabilization of intermediate energy-saturated states and meta-stable phase formation is discussed.