The piezoelectric effect of ZnO has been investigated recently with the goal to modify metal/semiconductor Schottky-barriers and p-n-junctions by application of mechanical stress. This research area called “piezotronics” is so far focused on nano structured ZnO wires. At the same time, ZnO varistor materials are already widely utilized and may benefit from a piezotronic approach. In this instance, the grain boundary potential barriers in the ceramic can be tuned by mechanical stress. Polycrystalline varistors exhibit huge changes of resistivity upon applied electrical and mechanical fields and therefore offer descriptive model systems to study the piezotronic effect. If the influence of temperature is contemplated, our current mechanistic understanding can be interrogated and corroborated. In this paper, we present a physical model based on parallel conducting pathways. This affords qualitative and semi-quantitative rationalization of temperature dependent electrical properties. The investigations demonstrate that narrow conductive pathways contribute to the overall current, which becomes increasingly conductive with application of mechanical stress due to lowering of the barrier height. Rising temperature increases the thermionic current through the rest of the material with higher average potential barriers, which are hardly affected by the piezoelectric effect. Hence, relative changes in resistance due to application of stress are higher at low temperature.
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28 August 2015
Research Article|
August 25 2015
Varistor piezotronics: Mechanically tuned conductivity in varistors
Raschid Baraki;
Raschid Baraki
1Institute of Materials Science,
Technische Universität Darmstadt
, Darmstadt 64287, Germany
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Nikola Novak;
Nikola Novak
1Institute of Materials Science,
Technische Universität Darmstadt
, Darmstadt 64287, Germany
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Michael Hofstätter;
Michael Hofstätter
2
Materials Center Leoben Forschung GmbH
, Leoben 8700, Austria
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Peter Supancic;
Peter Supancic
2
Materials Center Leoben Forschung GmbH
, Leoben 8700, Austria
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Jürgen Rödel;
Jürgen Rödel
1Institute of Materials Science,
Technische Universität Darmstadt
, Darmstadt 64287, Germany
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Till Frömling
Till Frömling
a)
1Institute of Materials Science,
Technische Universität Darmstadt
, Darmstadt 64287, Germany
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a)
Author to whom correspondence should be addressed. Electronic mail: [email protected]
J. Appl. Phys. 118, 085703 (2015)
Article history
Received:
April 24 2015
Accepted:
August 10 2015
Citation
Raschid Baraki, Nikola Novak, Michael Hofstätter, Peter Supancic, Jürgen Rödel, Till Frömling; Varistor piezotronics: Mechanically tuned conductivity in varistors. J. Appl. Phys. 28 August 2015; 118 (8): 085703. https://doi.org/10.1063/1.4929360
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