Non-ergodicity in α-praseodymium oxide

The alpha phase of PrO2-delta appears to violate the normal tenets of equilibrium thermodynamics in thermogravimetric experiments, in particular Gibbs Phase Rule. Isoplethic (equal concentration) replots of isobaric experiments were found to display four pseudophases in the alpha region instead of one. The opposite experiments - isobaric replots of isoplethic data also showed four unexpected phases . The direct experiments exhibit no subdivision of the a phase into four subphases, but the four pseudophases clearly revealed in each of the two derived plots do not appear to be the same. This unusual behaviour is shown to be due to the existence of several periodic invariant equilibrium states which lead to the violation of the Phase Rule and arise from the ergodic breakdown of the a phase into four pseudophases , each displaying strong path-dependent memory effects.