Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.

Mixed Valence Chemistry-A Survey and Classification

Publisher Summary The chapter presents a study on relations between the concentrations of imperfections in crystalline solids. Many properties of crystalline solids, such as the electronic or ionic conductivity, the color, the luminescence, and the magnetic susceptibility are determined by the presence of imperfections. Generally, six types of primary imperfections are distinguished; namely phonons, electrons and holes, excitons, vacant lattice sites and interstitial atoms or ions, foreign atoms or ions in either interstitial or substitutional positions, and dislocations. In addition atoms of the base crystal may be present at lattice sites normally occupied by other atoms. Five types of primary imperfections—namely, electrons and holes, vacant lattice sites, interstitials, misplaced lattice atoms, and foreign atoms—are discussed in this chapter. The chapter presents a new treatment of these problems by making use of a graphical representation. This treatment, together with the use of a band scheme for the electronic energy levels, greatly facilitates the application of the theory and the deduction of conclusions from it. Apart from a few exceptions, binary nonmetallic compounds of the formula M X will be considered almost exclusively. Here M indicates an element of a more electropositive character (metal) and X an element of a more electronegative character.

Relations between the Concentrations of Imperfections in Crystalline Solids

Ceria in automotive exhaust catalysts: I. Oxygen storage

Mixed oxides of the type MO2 (fluorite)—M2O3—I oxygen dissociation pressures and phase relationships in the system CeO2Ce2O3 at high temperatures

Ordered intermediate phases in the system CeO2Ce2O3

Die Phasenverhaltnisse der Ceroxyde zwischen CeO2 und Ce2O3 und der Praseodymoxyde zwischen PrO2 und Pr2O3 werden durch Rontgenuntersuchungen bestimmt. Beide Oxydsysteme erweisen sich in der Zahl der beobachteten drei Phasen als vollig ubereinstimmend und hinsichtlich der Ausdehnung dieser Phasen als sehr ahnlich. Die Dioxydphase mit Fluoritstruktur besitzt praktisch keine Homogenitatsbreite, die Sesquioxydphase vom hexagonalen A-Typ vermag ein wenig zusatzlichen Sauerstoff homogen aufzunehmen. Von diesen beiden Phasen getrennt liegt im Gebiet mittlerer Oxydationsgrade eine Zwischenoxydphase mit breitem Existenzbereich und einem Kristallgitter, das kontinuierlich vom Fluorit- zum C-Sesquioxydtyp ubergeht.

Über heterotype Mischphasen bei Seltenerdoxyden. II. Die Oxydsysteme des Cers und des Praseodyms

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Über heterotype Mischphasen bei Seltenerdoxyden. II. Die Oxydsysteme des Cers und des Praseodyms