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The electrical characteristics of highly dense SnO[sub 2] ceramic varistors are believed to be caused by the existence of potential barriers at the grain boundary. A complex plane analysis technique (to eliminate the influence of trapping activity associated with the conductance term observed via depression angle of a semicircular relaxation in the complex capacitance plane), allied with an approached Mott-Schottky model, are used to demonstrate that the potential barriers at the grain boundary are Schottky-type barriers in SnO[sub 2] varistors such as those observed in the traditional ZnO varistor. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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Mg2TiO4was synthesized by the polymeric precursor method, was doped with 1 mol% of Mn2+, Fe2+or Co2+. The powder precursors were characterized by TG/DTA methods. The mass loss took place in three steps. In the first one water and adsorbed gases were released while the second and third step were representative to the decomposition of the organic substance. The DTA experiments indicated the combustion as well as the decomposition and recrystallization of Mg2TiO4between 800 and 1200°C. XRD results indicated that spinel (AB2O4) which have been observed at 600°C transformed to ilmenite (MgTiO3) over 800°C. [ABSTRACT FROM AUTHOR]

In the recent years, the interest concerning to the synthesis of complex oxides, to be applied as electronic ceramics is continuously increasing. One good example is strontium titanate, displaying a perovskite structure, which favors the occurrence of important electronic properties. In the present study, SrxCo1-xTiO3powders, in which 0≤;x≤;0.3, were synthesized by the polymeric precursor method, achieving good a stoichiometric control and presented a crystalline structure at temperatures as low as 600°C. These systems were thermally and structurally characterized using thermogravimetric analysis (TG/DTA), X-ray diffraction (XRD) and infrared spectroscopy (IR). The TG results of the powder precursors show that the mass loss process observed for the undoped and Co-doped SrTiO3takes place in four well-defined stages. These stages are related to the evaporation of water and to the combustion of the organic matter present in the powder precursors (pyrolysis process). The addition of cobalt to the SrTiO3promotes a decrease in the mass loss and also decreases the final decomposition temperature of the organic matter. The XRD analysis showed a single phase when 10% of Sr2+was replaced by Co2+. When the extent of cobalt substitution was higher than 10 mol% and the substance was heat treated over 900°C, a CoTiO3secondary phase appeared. By means of IR, it was possible to observe the vibration bands related to the Ti-O bonds and to carbonates. [ABSTRACT FROM AUTHOR]