Commericially available BaTiO3 powder was die-pressed to discs, and sintered by a two-stage firing consisting of reducing in low oxygen partial pressures (pO2) and re-oxidizing in a higher pO2 to simulate the
industrial process of manufacturing the multi-layer ceramic capacitors(MLCC). Both undoped and MgO-doped discs as well as commercial MLCC chips, provided by Ferro Electronic Material Systems, have been investigated for sintered microstructures using the scanning electron microscopy (SEM) and transmission electron microscopy (TEM), crystalline phases using the X-ray diffractometry (XRD), and dielectric properties using the frequency response analysis. A comparison between the microstructures is made in order to look for the microstructure origin
of the macroscopic behaviour, e.g. dielectric properties.It is found that the crystalline phases have changed frompredominantly tetragonal to pseudo-cubic with MgO > 0.5 mol.%. Apart from grain growth being effectively suppressed in MgO-doped
compositions, grains containing the characteristic ferroelectric domains in undoped samples have decreased significantly in number. The indication
is that Mg2+ dissolving into the BaTiO3 lattice, substituting for the Ti4+ site reduces the c/a ratio. However, unlike what was reported before, no
direct experimental evidence is found to support that grain growth inhibition is effected by Mg2+ segregation to grain boundaries.Dislocation loops are observed ubiquitously in all samples, although bothMgO doping and low pO2 have decisive effect on their density in sintered grains. In MLCC chips, the microstructure is characterised by core-shell
grains representing the dissolution of solutes, and modulated grains representing the ordering of chemical defects, e.g. substitutional defects
and oxygen vacancies forming defect clusters.Residual pores located intragranularly in the MLCC chips are also observed, and its origin
discussed. The formation of such pores is attributed to vacancy condensation which is enhanced by the increased oxygen vacancies due to MgO doping, as an acceptor, and by low pO2 firing.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0806108-174705 |
| Date | 06 August 2008 |
| Creators | Lee, Hwan-Wen |
| Contributors | Bing-Hwai Hwang, Hong-Yang Lu, Yu-Chuan Wu |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0806108-174705 |
| Rights | campus_withheld, Copyright information available at source archive |
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