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

Periodicity in the band gap variation of Ln2X3 (X = O, S, Se) in the lanthanide series

The normal tungstates (R2O3·3WO3) of all rare‐earth elements have been prepared as well as the 1:1 oxytungstates (R2O3·WO3) of all except Sc and Ce. Physical properties were studied with particular emphasis on luminescence.

Rare-earth tungstates and 1 :1 oxytungstates

Publisher Summary This chapter focuses on the full range of binary rare earth oxide phases known to exist together with their concomitant structural, thermodynamic, and dynamic characteristics. The rare earths used here include the fifteen lanthanide elements and scandium and yttrium. This large group of elements with measured differences provides one of the best sources available for studying developing chemical and physical characteristics. They do not possess the full range of solid-state properties but they will be appreciated as one of the best model systems because they provide subtle variations in properties that may be utilized to test hypotheses or theories. In addition to their intrinsic theoretical interest and as models for other systems, the oxides of the rare earths have many practical uses. They receive attention in industry because of their potential use as control rods for nuclear reactors where samarium, gadolinium, and europium oxides are incorporated into cermets or are used in fuel elements as burnable poisons.

Chapter 27 The binary rare earth oxides

The reflectance spectra of forty metallic oxides and oxide-like materials have been obtained in the spectral region from 300 to 1000 millimicrons. The data are discussed in relation to the electronic structure of the materials.

The Reflectance Spectra of Metallic Oxides in the 300 to 1000 Millimicron Region

Reflectance spectra of praseodymium oxides in the composition range Pr2O3 to Pr6O11

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Reflectance spectra of praseodymium oxides in the composition range Pr2O3 to Pr6O11