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The Frequency Domain Thermoreflectance Technique for Thermal Property Measurements
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Local variability in PTC thermistor grain boundary structures.

C Leach1, J Seaton

  • 1Materials Science Centre, School of Materials, University of Manchester, Manchester M1 7HS, UK. Colin.leach@manchester.ac.uk

Scanning
|July 12, 2008
PubMed
Summary
This summary is machine-generated.

Scanning electron microscopy revealed distinct electrical properties at thermistor grain boundaries above the Curie temperature. Different structures, including Schottky barriers and n-i-n interfaces, were identified, influencing conductivity.

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Area of Science:

  • Materials Science
  • Condensed Matter Physics

Background:

  • Positive Temperature Coefficient (PTC) thermistors exhibit a sharp increase in resistance above their Curie temperature (T(C)).
  • Understanding the microstructural and electrical characteristics of grain boundaries is crucial for PTC thermistor performance.

Purpose of the Study:

  • To investigate the electrical properties of grain boundaries in a PTC thermistor using conductive mode (CM) scanning electron microscopy (SEM).
  • To differentiate the mechanisms contributing to CM contrast above and below the Curie temperature.

Main Methods:

  • Conductive mode microscopy with a remote electron beam-induced current (EBIC) configuration was employed.
  • Imaging was performed on a PTC thermistor sample at temperatures below and above its Curie temperature.

Main Results:

  • Below T(C), the thermistor showed low resistance with no significant CM contrast.
  • Above T(C), grain boundaries became resistive, displaying significant CM contrast attributed to three mechanisms.
  • Observed contrast mechanisms included resistive contrast, electron beam-induced current consistent with Schottky barriers, and beta-conductivity suggesting n-i-n structures.

Conclusions:

  • Electrically active grain boundaries with diverse structural characteristics coexist within the PTC thermistor.
  • The identified grain boundary structures (Schottky barrier, n-i-n) explain the observed electrical behavior above T(C).