Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Nanoscale Characterisation of Barriers to Electron Conduction in ZnO Varistor Materials
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science.
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work presented in this thesis is concerned with the microstructure of zinc oxide varistor materials used in surge protecting devices. This class of material has been characterised with special emphasis on the functional microstructure and the development of the microstructure during sintering. Several different techniques have been used for the analysis, especially scanning electron microscopy (SEM) in combination with electron beam-induced current (EBIC) analysis and in-situ studies of heat-treatment experiments and transmission electron microscopy (TEM) in combination with energy dispersive X-ray spectrometry (EDS) and electron holography.

Detailed TEM analyses using primarily centred dark-field imaging of grain boundaries, especially triple and multiple grain junctions, were used to reveal the morphological differences between the various Bi2O3 phases. The triple and multiple grain junctions were found to exhibit distinct differences in morphology, which could be attributed the difference in structure of the crystalline Bi2O3 polymorphs present in the junctions.

Electrical measurements were performed on individual ZnO/ZnO grain boundaries using EBIC in the SEM. The EBIC signal was found to depend strongly on the geometric properties of the interface and also on the symmetry of the depletion region at the interface. A symmetric double Schottky barrier was never observed in the experiments, but instead barriers with clear asymmetry in the depletion region. Experimental results together with computer simulations show that reasonably small differences in the deep donor concentrations between grains could be responsible for this effect.

Electron holography in the TEM was used to image the electrostatic potential variation across individual ZnO/ZnO interfaces. The sign of the interface charge, the barrier height (about 0.8 eV) and the depletion region width (100 to 150 nm) were determined from holography data. Asymmetries of the depletion region were also found with this technique.

The full sintering process of doped ZnO powder granules was studied in-situ in the environmental SEM. The densification and grain growth processes were studied through the sintering cycle. The formation of a functional microstructure in ZnO varistor materials was found to depend strongly on the total pressure.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2002. , p. 73
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 686
Keywords [en]
Materials science, ZnO varistor material, TEM, SEM, EBIC, ESEM, electron holography
Keywords [sv]
Materialvetenskap
National Category
Materials Engineering
Research subject
Solid State Physics
Identifiers
URN: urn:nbn:se:uu:diva-1757ISBN: 91-554-5236-1 (print)OAI: oai:DiVA.org:uu-1757DiVA, id: diva2:161335
Public defence
2002-03-08, Häggsalen, Ångströmlaboratoriet, Uppsala, 09:30
Opponent
Available from: 2002-02-15 Created: 2002-02-15Bibliographically approved

Open Access in DiVA

fulltext(2351 kB)7141 downloads
File information
File name FULLTEXT01.pdfFile size 2351 kBChecksum MD5
f4478d2abaa74151746930326badbc9f377ada7e0a4ecd3d18baaa44a73e5ca7f103f14a
Type fulltextMimetype application/pdf
Buy this publication >>

By organisation
Department of Materials Science
Materials Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 7141 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 1272 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf