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Start Over Author "Aldao A" Journal ceramics international
10 results on '"Aldao A"'

5. Different degradation processes in ZnO varistors

Author

Celso Manuel Aldao and Miriam Susana Castro

Subjects
Materials science, Dopant, Process Chemistry and Technology, Ion migration, Varistor, Mineralogy, Schottky diode, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, Chemical physics, Materials Chemistry, Ceramics and Composites, Degradation (geology), Grain boundary, Deformation (engineering), Current density
Abstract

Degradation of ZnO-based varistors has been attributed to ion migration in the depletion layers at intergrains. Experiments can then be explained as the result of the deformation of Schottky barriers present in the grain boundaries. However, the simple lowering of the barriers is not consistent with the observed results. We found that ion migration can change the dopant profile and then the barriers' shape. We found it necessary to distinguish two processes, permanent degradation and reversible degradation to account for the observed experimental results.

Published
1996

9. Resistance and capacitance analysis of Pd-doped and undoped SnO2 thick films sensors exposed to CO atmospheres

Author

Ponce, M.A., Castro, M.S., and Aldao, C.M.

Subjects
*THICK films, *CARBON monoxide, *STANNIC oxide, *PALLADIUM, *OXYGEN
Abstract

Abstract: It was found that resistance and capacitance of Pd-doped SnO2 thick films are largely modified by CO reaction with previous adsorbed oxygen at the grain surface while in undoped SnO2 thick-films adsorption and reaction processes influence the response. In our analysis, the presence of Schottky potential barriers at the grain boundaries was consistent with the observed results. An increasing of sensitivity due to the addition of Pd is found to be related to the enhanced reaction of CO with the previous oxygen adsorbed at the grains surface. Mechanisms responsible for the sensor response are discussed. [Copyright &y& Elsevier]

Published
2006
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10. Electrical and microstructural properties of (Zn, Nb, Fe)-doped SnO2 varistor systems

Author

Parra, R., Varela, J.A., Aldao, C.M., and Castro, M.S.

Subjects
*MICROSTRUCTURE, *PROPERTIES of matter, *VARISTORS, *ELECTRIC fields, *ELECTRIC currents, *SPECTRUM analysis
Abstract

Abstract: The electrical and microstructural properties of SnO2-based varistors with the addition of 0.025 and 0.050mol% of Fe2O3 have been characterised. Electric field (E) versus current density (J) curves showed that the effect of Fe2O3 addition is to increase both the non-linear coefficient and the breakdown voltage. Variations in the potential barrier height were inferred from impedance spectroscopy (IS) analysis. Through transmission electron microscopy (TEM), the presence of precipitates of secondary phases was confirmed. Samples with precipitates displayed poor electrical properties. [Copyright &y& Elsevier]

Published
2005
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