Determination of phase equilibria in complex oxide systems by mass-loss knudsen effusion

The mass-loss Knudsen effusion experiment is described as a primary and efficient means for characterizing, at temperature and under equilibrium conditions, the accurate location of all non-isothermal high temperature phase boundaries in any multicomponent material system that incongruently, and preferentially, vaporizes a single subcomponent.The isothermal equilibrium effusion of the volatile subcomponent is monitored continuously by recording the mass-loss of a Knudsen cell containing a condensed sample of pre-determined composition. The rate of mass-loss is a function of the continuously changing composition of the condensed sample. Consequently, a single experiment can provide several points along either a solidus or liquidus, as well as describing the isothermal nature and extent of single-phase nonstoichiometry.The method is applicable, for example, to a wide range of complex lead, molybdenum, bismuth, lithium, sodium, and tin oxide systems. The ferroelectric PbO-TiO2 binary is selected for illustration.