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- Title
The influence of area/volume ratio on microstructure and non-Ohmic properties of SnO<sub>2</sub>-based varistor ceramic blocks.
- Authors
Ramírez, M. A.; Fernández, J. F.; De la Rubia, M.; de Frutos, J.; Bueno, P. R.; Longo, E.; Varela, J. A.
- Abstract
This work deals with the electrical properties of SnO2-based varistor systems with different area–volume (A/V) ratio of the green compact. The influence of A/V ratio specially on microstructural homogeneity and different diameter-thickness (D/t) ratio of sintered compact mainly as a requisite to the existence of non-Ohmic properties is evaluated. The results evidence that, contrary of what is generally observed for ZnO-based varistor system, in the SnO2-based system, the A/V ratio of the green compacts does not influence the non-Ohmic properties, i.e. the homogeneity of the microstructure and the composition after sintering is conserved independently of the A/V ratio employed in the green compacts. Such independence was specifically observed by performing non-Ohmic measurement after cutting the sintered blocks in different slices and observing that the current–voltage curve of the slices are very similar for different A/V ratio of the green compacts before sintering. The observed behavior has its origin on the fact that A/V ratio does not affect the microstructure development during sintering due to the minimal CoO losses by vaporization for SnO2-based system, i.e. the stability of the dopant oxides is high when compared with that used in commercial ZnO · Bi2O3-based varistors in which, for instance, Bi2O3 volatilizes critically. On the other hand, it was found a critical value of A/V = 5.0 cm−1 for the ceramic blocks to effectively served as varistor, below this ratio the ceramics were highly resistive because of a high number of effective barriers ∼85% which is higher than normally found for ZnO-based systems (35%).
- Subjects
VARISTORS; STANNIC oxide; SINTERING; ELECTRONIC ceramics; MICROSTRUCTURE; SEMICONDUCTOR diodes; ZINC oxide; COBALT compounds; BISMUTH trioxide
- Publication
Journal of Materials Science: Materials in Electronics, 2009, Vol 20, Issue 1, p49
- ISSN
0957-4522
- Publication type
Article
- DOI
10.1007/s10854-008-9602-8