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.

I. Non-stoichiometry and Defect Structure.- The Control of Stoichiometry in Oxide Systems.- Phase Relations of Metal Oxides by Coulometric Titration.- Defect Structure and the Related Properties of UO2 and Doped UO2.- Defect Interactions, Extended Defects and Non-stoichiometry in Ceramic Oxides.- Computer Simulation Studies of Fe1?xO and Mn1?xO.- Mott-Littleton and Hartree-Fock Calculations on Defects in ?-Quartz.- Point Defect Structure of Chromium (III) Oxide.- Non-stoichiometry and Defect Structure of FeO.- Thermodynamic and Structural Evidence for the Presence of Defect Clusters in Some Non-stoichiometric Oxides.- Defect Chemistry of BaTiO3 and SrTiO3: Practical Aspects and Application to Electronic Ceramics.- Statistical Thermodynamics of Non-stoichiometric Oxides.- Electrical Conductivity Study of Cobalt Molybdate CoMoO4.- Electronic Structure of Transition Metal Impurities and of Surface Defects in SrTiO3.- Cation Distribution and Non-stoichiometry in MnCr2O4-NiCr2O4 Spinel Solid-Solutions.- II. Surface and Grain Boundary Phenomena.- Characterization of Defects on Oxide Surfaces and Their Impact on Surface Reactivity and Catalysis.- Interface Transport in Monoxides.- ZnO Interface Electrical Properties-Role of Oxygen Chemisorption.- Near-Surface Defect Structure of CoO in the Vicinity of the CoO/Co3O4 Phase Boundary.- Grain Boundary Phenomena in Some Electronic and Magnetic Ceramics.- Surface Oxygen Exchange in Bismuth Oxide Based Materials.- Defects and Reactivity at Oxide Surfaces: Experimental Aspects of the Interaction of Hydrogen, CO and CO2 with the NiO ?001? Surface311.- Nuclear Techniques in Surface Studies of Ceramics.- Calculated Grain Boundary Structures in NiO: Comparison with Experiment.- III. Transport Properties.- Oxygen Self Diffusion inSynthetic Rutile under Hydrothermal Conditions.- Short-Circuit Diffusion in ?Al2O3.- Oxygen Self-Diffusion in Volume and in Grain Boundaries of Cu2?xO.- Defect Structure and Diffusion in Mg2SiO4 (Forsterite) at High Temperature.- Influence of Chromium Segregation on the Transport Properties of Iron Monoxide.- Influence of Point Defects on the Near-Surface Diffusion in Some Oxide Systems.- IV. High Tc Oxide Superconductors.- Static Simulation Studies of La2CuO4.- Defects and Transport in YBa2Cu3O7?x.- Oxygen Nonstoichiometry and Chemical Diffusion Coefficient of Oxygen in Ba2YCu3O7?xO.- Point Defects and Transport in Small Polaron Systems.- Electronic Structure of High Tc Cuprates by Electron Spectroscopies.- Nonstoichiometry and Defect Equilibria in YBa2Cu3Ox.- V. Redox Processes.- Model Calculations of Metal Oxidation at Ambient Temperatures.- Point Defects and the Mechanisms Involved in the Reduction of Hematite into Magnetite.- Joining of Metallic Grains by Thermal Oxidation.- Impedance and Voltage Relaxation Studies of the Oxygen Sensor Systems Pt/O2/YSZ, Pt/O2/TiO2 and Pt/O2/?-Bi2O3.