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

The development of a quantitative model that correlates conduction in and sensing with p-type gas sensitive metal oxides is presented here. The theoretical results are confronted with the experimental data and found to be in very good agreement. The model also explains the differences between the performance of gas sensors based on n and p-type metal oxides and indicates the possible improvement routes.

Modeling of sensing and transduction for p-type semiconducting metal oxide based gas sensors

Publisher Summary This chapter discusses electronic processes in zinc oxide. Zinc oxide, ZnO, occurs in nature as the mineral zincite. It is produced in large quantities in the smelting of zinc ores and can be prepared in pure form by burning of zinc in air or by calcining zinc hydroxide, zinc carbonate, or zinc nitrate. It has been used for a long time as a pigment for paints and in enamel coatings, as an activator for the acceleration of vulcanization of rubber and as a pharmaceutical in zinc salves. Of the applications which depend in a direct way on the electronic processes in zinc oxide, one should mention, first of all, its use as a catalyst and as a photocatalyst for a series of chemical reactions. Its use in the vulcanization of rubber mentioned above is a good example (“active zinc oxide”). Zinc oxide crystallizes in the hexagonal wurtzite lattice in which the oxygen ions are arranged in closest hexagonal packing and the zinc ions occupy half of the tetrahedral interstitial positions and have the same relative arrangement as the oxygen ions.

Electronic Processes in Zinc Oxide

Publisher Summary The transition metals are interesting because, in addition to the s and p electrons found on each atom of ordinary metals, their atoms each possess from one to nine d electrons When these transition metal atoms overlap to form a solid, the d orbitals spread to form a relatively narrow d band This d band is partially full, and is primarily responsible for the magnetic properties of the materials The next higher s band is quite wide, and overlaps the entire d band Thus, there is always a partially full s band that results in metallic conductivity This chapter discusses the oxides of the transition metals The main part of this chapter is a discussion of the models that have been presented to explain the nonconductivity of the ground state It also reviews in detail, the experimental results on a number of specific materials, and then considers how successful the models are in explaining the actual observations

Insulating and Metallic States in Transition Metal Oxides

Über die Sauerstoffdruckabhängigkeit der elektrischen Leitfähigkeit einiger Mischoxyde

Fehlordnungsmodell eines Eigenstörstellen-Halbleiters am Beispiel des Chromoxyds

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Über die Sauerstoffdruckabhängigkeit der elektrischen Leitfähigkeit einiger Mischoxyde

Fehlordnungsmodell eines Eigenstörstellen-Halbleiters am Beispiel des Chromoxyds