Well-known perovskites (cerates, cuprates, manganates): Problems and facts; A review of nontraditional approaches

Abstract

Phenomena and processes either new or not studied in-depth occurring in perovskite oxides and in systems which contain these compounds are reported and summarized. The materials under consideration are well-known for specific properties, e.g., cerates of alkaline earths are high-temperature proton conductors, manganates are electrode materials of SOFCs and show the effect of colossal magnetoresistance or YBa₂Cu₃O₇ cuprates YBa₂Cu₃O₇ are “high-temperature” superconductors. The presented nontraditional approach consists of considering physical and chemical phenomena and processes, which do not relate to the indicated main properties of the compounds. For instance, BaCeO₃ undoped and slightly doped has partially cerium in the form of Ce⁺³, which provides the effect of blue luminescence which is controlled by thermochemical treatment; H₂YBa₂Cu₃O₇ manifests mixed proton-electron conduction at 400–550 K under water vapor of 100–300 Pa; La_0.67Ca_0,33MnO_2.84 can dissolve some part of water vapor as this occurs in traditional HTPC. The electrochemical cells Pd | HTPC | hydrocuprate | HTPC | Pd and the more simple one Pd | HTPC | Pd show e.m.f. values near 1 V under certain conditions after polarization by d.c. currents at 420–520 K under different atmospheres. The system water vapor — membrane of undoped BaCeO₃-hydride is described. Defect chemistry equations are used to describe some of the phenomena which are employed for the production and storage of pure hydrogen.