Nonstoichiometric Oxides discusses the thermodynamic and structural studies of nonstoichiometric oxides. This eight-chapter text also covers the defect-defect interactions in these compounds. The introductory chapters describe the thermodynamic properties of nonstoichiometric oxides in terms of defect complexes using the classical thermodynamic principles and from a statistical thermodynamics point of view. These chapters also include statistical thermodynamic models that indicate the ordered nonstoichiometric phase range in these oxides. The subsequent chapters examine the transport properties, such as diffusion and electrical conductivity. Diffusion theories and experimental diffusion coefficients for several systems, as well as the electrical properties of the highly defective ionic and mixed oxide conductor, are specifically tackled in these chapters. The concluding chapters present the pertinent results obtained in nonstoichiometric oxide structural studies using high-resolution electron microscopy and X-ray and neutron diffraction. Inorganic chemists and inorganic chemistry teachers and students will greatly appreciate this book.

The interrelation among composition, microstructure, and properties of stoichiometric and nonstoichiometric compounds is a major field of research for both scientific and technological reasons. As such, this book focuses on metal oxides, which present a large diversity of electrical, magnetic, optical, optoelectronic, thermal, electrochemical, and catalytic properties, making them suitable for a wide range of applications. By bringing together scientific contributions with special emphasis on the interrelations between materials chemistry, processing, microstructures, and properties of stoichiometric and nonstoichiometric metal oxides, this book highlights the importance of tightly integrating high-throughput experiments (including both synthesis and characterization) and efficient and robust theory for the design of advanced materials.

The material in this book is based on invited and contributed pa pers presented at the NATO Advanced Research Workshop on INon-stoichio l metric Compounds held in Ringberg Castle, Rottach-Egern (Bavarian Alps), Germany, July 3-9, 1988. The workshop followed previous meetings held in Mogilany, Poland (1980), Alenya, France (1982), Penn State, USA (1984) and Keele University, UK (1986). The aim of these workshops is to present and discuss up-to-date knowledge in the study of non-stoichiometry and its effect on materials properties as well as to indicate the most urgent research pathways required in this field. Since the subject of non-stoichiometry is interdisciplinary, the workshops bring together solid state physicists and chemists, surface scientists, materials scientists, ceramists and metallurgists. The present workshop, which gathered 42 scientists of an inter national reputation, mainly considered the effect of surfaces, grain boundaries and structural defects on materials properties. From discus sions during this meeting it emerged that correct understanding of properties of ceramic materials requires urgent studies on the defect structure of the interface region. Progress in this direction requires the development of the interface defect chemistry. This is the task for materials scientists in the near future. The present proceedings includes both theoretical and experimen tal work on general aspects of non-stoichiometry, defect structure and diffusion in relation to the bulk and to the interface region of such materials as high tech ceramics, solid electrolytes, electronic cera mics, nuclear materials and high Tc oxide superconductors.

The advancement of material engineering over the last few decades has allowed for the development of modern metallic and ceramic construction materials, composites, nanomaterials and various kinds of coatings with desired performance characteristics. They form the basis for the development of the automotive industry, the aviation industry, the chemical equipment industry, etc. They can function in ever higher temperatures and aggressive environments. On the other hand, the advancement of electronics requires the development of new and cheaper materials: semiconductors, insulators, materials with magnetic, ferrimagnetic or piezoelectric properties, etc. The desired properties of materials or their surface layers depend on chemical composition, dopants, and the concentration of point defects, through which the transport of ions and electrons takes place. The functional properties also depend on the nuances of production technologies which allow to obtain a specific texture and a desired concentration of ionic and electronic point defects. The monograph follows up on the issues related to the concentration of charge carriers in pure and doped oxides. Based on the diagrams of the concentration of point defects, the calculation results of the concentration of charge carriers and their mobility are presented, using the results of the studies on the electrical conductivity and the thermoelectric power in some specific oxides of 3d metals. In turn, the results of calculations of the ionic defect diffusion coefficients, conducted using the coefficients of self-diffusion and chemical diffusion as well as the concentration of ionic defects in these oxides, are presented. The given material will be useful to a wide range of researchers and developers of new materials with a wide range of required properties.

In the present work, in Part I, new elements widening the bases of the defects theory are shown; particularly, this work discusses the mechanism of the formation of defects as a result of elementary processes; the work also presents a description of the equilibrium state by one equation, taking into account the concentrations of defects and their changes during the process of reaching the equilibrium. The equation relates the concentrations of defects, dependent on the standard Gibbs energies of their formation, with the equilibrium pressure of oxygen. The obtained relations and the discussion have lead to the development of a method for determination of complete diagrams of concentrations of the point defects, which allows taking into account the minority defects. Part II presents the results of the calculations of the diagrams of point defects’ concentrations for a series of pure and doped oxides of transition metals 3d, with different composition (M/O ratio), crystallographic structure and point defects’ structure. A critical analysis of the results of the studies of the deviation from the stoichiometry and the electrical conductivity, obtained (so far) by most research groups has been also performed. A new interpretation of these results, concerning concentrations and types of ionic defects present has been performed and the mobility of electronic defects and its dependence on the temperature and oxygen pressure have been determined.

This unified presentation of the chemistry of non-stoichiometric compounds is the first monograph on the subject for two decades. Based on statistical thermodynamics and structural inorganic chemistry, with descriptions of modern examples and applications, this will be useful to both researchers in industry and undergraduates in solid state chemistry and physics.