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Nonlinear Lock-In Infrared Microscopy: A Complementary Investigation Technique for the Analysis of Functional Electroceramic Components

Published online by Cambridge University Press:  14 May 2015

Michael Hofstätter ,
Nadine Raidl ,
Bernhard Sartory  and
Peter Supancic
Michael Hofstätter
Affiliation:
Institut für Struktur- und Funktionskeramik, Montanuniversitaet Leoben, 8700 Leoben, Austria
Nadine Raidl
Affiliation:
Institut für Struktur- und Funktionskeramik, Montanuniversitaet Leoben, 8700 Leoben, Austria
Bernhard Sartory
Affiliation:
Materials Center Leoben Forschung GmbH, Roseggerstraße 12, 8700 Leoben, Austria
Peter Supancic*
Affiliation:
Institut für Struktur- und Funktionskeramik, Montanuniversitaet Leoben, 8700 Leoben, Austria Materials Center Leoben Forschung GmbH, Roseggerstraße 12, 8700 Leoben, Austria
*
*Corresponding author. peter.supancic@unileoben.ac.at
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Abstract

Using lock-in infrared microscopy as a tool for current detection on the micrometer scale in AC-driven specimens in combination with iterative grinding procedure allows preparation of current dominating microstructure regions on well-polished surfaces. This technique is applied successfully on varistor components based on specially doped ZnO-based varistor ceramics. This peculiar electroceramic material exhibits exceptional high nonlinear current–voltage (I-V) characteristics, described by a power law according I~Vα, caused by double Schottky barriers at the grain boundaries. As a novelty the thermographic response is used to evaluate local electrical properties, namely the nonlinearity coefficient α, on basis of higher order harmonics with respect to the basic electrical driving AC-frequency.

To correlate the observed electrical properties to the microstructure, the polar crystal orientation of the relevant ZnO grains is determined by combining electron backscatter diffraction and orientation-dependent patterns as a result of a chemical etching procedure. These findings support a modified new model for describing the grain boundary controlled current flow in a varistor microstructure including orientation-dependent barrier properties. Hence, the experimentally observed current direction-dependent behavior can be described consistently.

Keywords

thermographyelectroceramic materialsSchottky barrierszinc oxidevaristor
Type
EMAS Special Issue
Information
Microscopy and Microanalysis , Volume 21 , Issue 5 , October 2015 , pp. 1145 - 1152
Copyright
© Microscopy Society of America 2015 

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Footnotes

This article is intended for the Special Issue from the EMAS 2014 Workshop on Electron Probe Microanalysis of Materials Today—Rare and Noble Elements: From Ore Deposits to High-Tech Materials.

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