Anatase nanoparticles were obtained through a modified sol–gel route from titanium isopropoxide modified with acetic acid in order to control hydrolysis and condensation reactions. The modification of Ti(O i Pr)4 with acetic acid reduces the availability of groups that hydrolyze and condense easily through the formation of a stable complex whose structure was determined to be Ti(OCOCH3)(O i Pr)2 by means of FTIR and 13C NMR. The presence of this complex was confirmed with FTIR in the early stages of the process. A doublet in 1542 and 1440 cm−1 stands for the asymmetric and symmetric stretching vibrations of the carboxylic group coordinated to Ti as a bidentate ligand. The gap of 102 cm−1 between these signals suggests that acetate acts preferentially as a bidentate rather than as a bridging ligand between two titanium atoms. The use of acetic acid as modifier allows the control of both the degree of condensation and oligomerization of the precursor and leads to the preferential crystallization of TiO2 in the anatase phase. A possible reaction pathway toward the formation of anatase is proposed on the basis of the intermediate species present in a 1:1 Ti(O i Pr)4:CH3COOH molar system in which esterification reactions that introduce H2O into the reaction mixture were seen to be negligible. The Rietveld refinement and TEM analysis revealed that the powder is composed of isotropic anatase nanocrystallites.

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Zinc oxide, ZnO, is a very interesting compound in science and electronic ceramics technology. ZnO ceramics containing some additives were reported to show varistor action with excellent nonlinearity in current - voltage characteristics. However, investigations were restricted to the ZnO - Bi2O3 ceramic system. Other type of varistor, which contains praseodymium oxide, also present nonlinear behaviour. In this work, results obtained in the synthesis Zn-Pr-Co powder are shown. In order to determine and control the several stages of the chemical method, potentiometric titration was used. The solid phase obtained was pressed and sintered

Among the mechanisms suggested to account for degradation of varistor materials. ion migration has slrong supprL Mobile. positively charged ions in the depletion layer would be the key element in degradation In this context, we discuss the wnsequenees of an electrical soessing on the cmt-temperature characteristic of a commercial varistor.ZnO-based ceramic varistors are semiconductor devices presenting a highly non-linear current-voltage characteristic. Their electrical behaviour is similar to that of two backto-back Zener diodes but with much greater current and energy capabilities. The advent of