Context
Structural and transport properties of nanocrystalline $LaMnO_{3}$ powders prepared by low temperature route
Title:
Structural and transport properties of nanocrystalline $LaMnO_{3}$ powders prepared by low temperature route
Archive:
Eprints@iisc
Author(s):
Date:
2005-01-01
Abstract:
Nanocrystalline $LaMnO_{3}$ has been synthesized by a low temperature initiated-self propagating, gas producing solution combustion process using nitrates of lanthanum and manganese as oxidizers while oxalyl dihydrazide (ODH) as a fuel. Combustion synthesis is rather cheap in terms of reactants employed, requires only few minutes without any successive calcination yields nanocrystalline products with large surface area. Studies have been performed on nanocrystalline powders using XRD, SEM, TG-DTA, FTIR and low temperature resistivity down to 77 K. The XRD patterns of as formed $LaMnO_{3}$ shows cubic phase, however on calcination (900 ºC, 6 h) it transforms to rhombohedral phase. The $Mn^{4+}$ content in as made $LaMnO_{3}$ is high (~34 %) and the cubic phase is favored. In calcined (900 ºC, 6 h) $LaMnO_{3}$ sample, $Mn^{4+}$ content is reduced to ~ 28 % and it attains to rhombohedral phase. The surface area of as synthesized compound is 24 $m^{2}/g$, on calcination it decreases to 12.5 $m^{2}/g$. From thermal analysis it is found that there is a broad exothermic peak around 900 0C. TG curve exhibits a gradual weight loss at around 650 ºC onwards corresponding to reduction of $Mn^{4+}$ to $Mn^{3+}$. $LaMnO_{3}$ powder shows two active IR vibrational modes at 400 and 600 $cm^{-1}$. The effect of the ratio of fuel/ oxidizer in the redox mixture has been investigated. XRD data and SEM micrograph show that crystallite size increases with an increase in fuel quantity. The electrical resistivity measurement is carried out on sintered pellets (900 ºC, 6 h) using dc four probe method in the range 77 - 300 K. $LaMnO_{3}$ sample exhibits a distinct metal insulator behavior with $(T_{M-I})$ at 223 K.
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Discipline(s):
Solid State & Structural Chemistry Unit
Subject(s):
Physics
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Type:
Conference Proceedings
Format:
pdf http://eprints.iisc.ernet.in/secure/00003826/01/2.pdf
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