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The Change in Oxidation State of Mn Ions in Semiconducting $BaTiO_3$ and $SrTiO_3$ Around the Phase Transition Temperatures

Kutty, TRN and Devi, Gomathi L and Murugaraj, P (1986) The Change in Oxidation State of Mn Ions in Semiconducting $BaTiO_3$ and $SrTiO_3$ Around the Phase Transition Temperatures. In: Materials Research Bulletin, 21 (9). pp. 1093-1102.

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The oxidation states of Mn in low concentration (< 0.1 atom%) in donor doped $BaTiO_3$ and $SrTiO_3$ have been studied using EPR, optical absorption spectra and electrical resistivity measurements. Mn substituting at the Ti-sites exists as $Mn^{2+}$ in the cubic and rhombohedral phases and as $Mn^{3+}$ in the tetragonal and orthorhombic phases of $BaTiO_3$. The change in oxidation state arises from the charge redistribution among singly- or doubly- ionised acceptor states and the conduction electron, depending upon the structural changes in the host lattice. The gain in Jahn-Teller energy stabilises $Mn^{3+}$ in the tetragonal and orthorhombic phases. In $SrTiO_3$, co-existence of $Mn^{2+}$, $Mn^{3+}$ and $Mn^{4+}$, together with $Mn^{2+}$ − $V_O$ is observed. Only $Mn^{2+}$ in $SrTiO_3$ converts to $Mn^{3+}$ as the lattice approaches $T_C$ (106 K). The electron loss (or hole gain) by the corresponding acceptor states may involve vibronic interactions and is influenced by the soft phonon modes. The acceptor states are more sensitive to local structural deviations and the facile redistribution of charges at the acceptors leads to the changes in resistivity around the phase transitions.

Item Type: Journal Article
Publication: Materials Research Bulletin
Publisher: Elsevier Science
Additional Information: Copyright of this article belongs to Elsevier Science.
Keywords: BaTiO3;SrTiO3
Department/Centre: Division of Chemical Sciences > Materials Research Centre
Date Deposited: 03 Apr 2008
Last Modified: 19 Sep 2010 04:44
URI: http://eprints.iisc.ac.in/id/eprint/13583

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