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EPR evidence for activation of trap centers in PTCR $BaTiO_3$ ceramics

Kutty, TRN and Murugaraj, P and Gajbhiye, NS (1985) EPR evidence for activation of trap centers in PTCR $BaTiO_3$ ceramics. In: Materials Research Bulletin, 20 (5). pp. 565-574.

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Donor-doped $BaTiO_3$ ceramics, exhibiting PTCR, showed an EPR signal with g=1.997 which acquires high intensity above $T_C$. This is indicative of activation of the corresponding defect centers, possibly $V′_{Ba}$.. The intensity of g=1.997 varies with Ba/Ti ratio, rate of cooling from the sintering temperature and the addition of $TiO_2$ as sintering agent. The signal intensity decreases with increase in grain size and is weak in La-doped $BaTiO_3$ single crystals. Therefore the concentration of $V_{Ba}$ is more around the grain boundaries than that in the bulk of grains. Activated trap centers around $T_C$ also arises from background impurities; those with change of electronic state: $M^{n+1}$+ e′ = $M^{n+}$ (eg:-Mn) and those associated with oxygen vacancies: $M^{P+}-V_O(e′)$ $(eg:-Fe^{3+})$. Activation of these trap centers are not dependent on the disappearance of spontaneous polarization but to the structural changes during phase transformation. The trapped charge carriers are not available for conduction and hence the increase in electrical resistivity.

Item Type: Journal Article
Publication: Materials Research Bulletin
Publisher: Elsevier BV.
Additional Information: Copyright of this article belongs to Elsevier BV.
Department/Centre: Division of Chemical Sciences > Materials Research Centre
Date Deposited: 11 Jul 2008
Last Modified: 19 Sep 2010 04:47
URI: http://eprints.iisc.ac.in/id/eprint/14952

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