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

The rapidly expanding field of nonaqueous multivalent intercalation batteries offers a promising way to overcome safety, cost, and energy density limitations of state-of-the-art Li-ion battery technology. We present a critical and rigorous analysis of the increasing volume of multivalent battery research, focusing on a wide range of intercalation cathode materials and the mechanisms of multivalent ion insertion and migration within those frameworks. The present analysis covers a wide variety of material chemistries, including chalcogenides, oxides, and polyanions, highlighting merits and challenges of each class of materials as multivalent cathodes. The review underscores the overlap of experiments and theory, ranging from charting the design metrics useful for developing the next generation of MV-cathodes to targeted in-depth studies rationalizing complex experimental results. On the basis of our critical review of the literature, we provide suggestions for future multivalent cathode studies, including a...

Odyssey of Multivalent Cathode Materials: Open Questions and Future Challenges

Chemical deposition method for metal chalcogenide thin films

A theoretical overview of the cooperative Jahn-Teller effect in the insulating phase is given. We obtain an effective Hamiltonian of an interaction between the orbital states of the Jahn-Teller ions through a canonical transformation, which associates each electronic state with a local lattice distortion, and by use of the mean field approximation. The effective Hamiltonian yields a simple unified picture of cooperative distortions of various types. The competing effect of the spin-orbit coupling is discussed also. Electron itinerancy is briefly discussed at the end.

Crystal Distortion in Magnetic Compounds

The co-operative Jahn-Teller effect is a phase transition which is driven by the interaction between localized orbital electronic states and the crystal lattice. The possible origins, symmetries and properties of the electron-lattice interactions and how they lead to possible hamiltonians for the coupled system are discussed. The relation of these interactions with quadrupolar interactions and magnetostriction is included. The methods of solution of the hamiltonians lead to an understanding of the electronic states, the phonon spectrum and the mixed normal modes. The wide variety of experimental techniques used on this problem are reviewed in detail and the results are compared with theoretical expressions whenever possible. The application of external stress and magnetic field is of particular significance in the case of the rare earth compounds, because they can product effects which are larger than the low-temperature spontaneous effects.

http://iopscience.iop.org/article/10.1088/0034-4885/38/1/001/pdf

Co-operative Jahn-Teller effects

A new technique for the preparation of CdS thin films by chemical bath deposition is described. The CdS films prepared by this method have many of the advantages of those made by the spray deposition method, such as the ease of coating large areas and simplicity of the process. The stoichiometry is easy to maintain in both these methods. The films are formed on rotating substrates from a bath containing cadmium salt in a complex form. Electrical, photoconducting, and optical properties such as I--V characteristics, decay of photoconductivity, spectral response of photoconductivity, and optical absorption were studied. Addition of cations like Ag, Cu. In, and Zn to the deposition bath makes the films amorphous. Such amorphous layers have a density of state of the order of 10/sup 19/--10/sup 20//cm/sup 3//eV near the Fermi level, as determined by photodecay and field effect measurements. The films produced are strong, adhering tightly to the substrates, show little or no degradation, and are photosensitive as deposited.

Photoconductive CdS Films by a Chemical Bath Deposition Process

Photoelectron-spectroscopic study of nickel, manganese and cobalt selenides

On the structure of some anganites

Effect of temperature on the structure of manganites

Antimony-doped SnO2 films with a resistivity as low as 9×10−4 Ωcm were prepared by spray pyrolysis. Structural, electrical and optical properties were studied by varying the antimony concentration, film thickness and deposition temperature. About 94% average transmission in the visible region and about 87% infrared reflectance were obtained for antimony-doped SnO2 films by a systematic optimization of the preparation parameters. As the best combination, an average transmission of 88% in the visible region and an infrared reflectance of 76% was possible for the doped SnO2 films.

A.P.B. Sinha

Papers

Photoconductive CdS Films by a Chemical Bath Deposition Process

Photoelectron-spectroscopic study of nickel, manganese and cobalt selenides

On the structure of some anganites

Effect of temperature on the structure of manganites

Deposition of improved optically selective conductive tin oxide films by spray pyrolysis