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Crystal structure, thermal expansion and electrical conductivity of $Nd_{0.7} Sr_{0.3} Fe_{1-x}Co_xO_3$ (0 \leq x \leq 0.8)

Dasgupta, Niladri and Krishnamoorthy, R and Jacob, KT (2001) Crystal structure, thermal expansion and electrical conductivity of $Nd_{0.7} Sr_{0.3} Fe_{1-x}Co_xO_3$ (0 \leq x \leq 0.8). In: High Temperature Materials and Processes, 20 (5-6). pp. 367-376.

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Abstract

The crystal structure, thermal expansion and electrical conductivity of the solid solutions $Y_{0.8}Ca_{0.2}Fe_{1-x} MnxO_3$ + \delta (0 \leq x \leq 1.0) were investigated. All compositions had the $GdFeO_3$-type orthorhombic perovskite structure with trace amounts of a second phase present in case of x = 0.8 and 1.0. The lattice parameters were determined at room temperature by using X-ray powder diffraction (XRPD). The pseudo-cubic lattice constant decreased with increasing x. The average linear thermal expansion coefficient (a,,) in the temperature range from 673 to 973 K showed negligible change with x up to x = 0.4. The thermal expansion curve for x = 1 had a slope approaching zero in the temperature range from 648 to 948 K. The calculated activation energy values for electrical conduction indicate that conduction occurs primarily by the small polaron hopping mechanism. The drastic drop in electrical conductivity for a small addition of Mn (0 less than or equal to x less than or equal to 0.2) is caused by the preferential foil-nation of $Mn^{4+}$ ions (rather than $Fe^{4+}$)which act as carrier traps. This continues till the charge compensation for the divalent ions on the A-site is complete. The results indicate that with further increase in manganese content (beyond x = 0.4) in the solid solutions, there is an increase in excess oxygen and consequently, a small increase in Mn4+ ions which are charge compensated by the formation of cation vancancies.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Freund Publishing House.
Department/Centre: Division of Chemical Sciences > Materials Research Centre
Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 11 Aug 2008
Last Modified: 27 Aug 2008 13:42
URI: http://eprints.iisc.ernet.in/id/eprint/15523

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