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The Investigation of PTC Effects of Barium Titanate Prepared from Nano-Structural BaTiO3 by Two Step Sintering Method

Esmaeili Rad, Ahmad | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41475 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Nemati, Ali
  7. Abstract:
  8. The PTC effect which is one of the most important properties of electroceramics is being used in lots of electrical devices. This effect is observed in ceramics based on Barium Titanate. In the present study, the effects of grain size and two-step sintering method on PTC effect of Barium Titanate were investigated and La2O3 was used as an additive to improve the PTC effect and sintering behaviors of BaTiO3. Characterization analysis showed that the BaTiO3 powders had Cubic structure up to 700°C and Tetragonal structure at 1150°C. The FE-SEM analysis and density analysis showed that the samples which were two-step sintered at T1 less than 1200°C only reached 90% of relative density. Under these conditions, samples did not show the PTC effect because the grain size was less than the minimum size required for PTC effect. The samples sintered at T1 of 1250°C reached 96% of relative density. The PTC effect was improved by increasing temperature, time of sintering and grain size up to 1.9 µm. It was also observed that the minimum grain size which showed PTC effect was about 0.4 µm. The sample which was two-step sintered at T1 of 1250°C and T2 of 1150°C for 30 hours reaching relative density about 96%, showed the best PTC effect. This sample exhibited a change in resistivity by a factor of 104.8 or even more
  9. Keywords:
  10. Barium Titanat ; Two Step Sintering ; Positive Temperature Coefficient (PTC)Effect ; Electro Ceramics

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