Context
Structural and metal-insulator transition studies on nanocrystalline $La_{1-x}Ba_{x}MnO_{3}$ (0 leq x leq 0.3) manganites
Title:
Structural and metal-insulator transition studies on nanocrystalline $La_{1-x}Ba_{x}MnO_{3}$ (0 leq x leq 0.3) manganites
Archive:
Eprints@iisc
Author(s):
Date:
2005-01-01
Abstract:
Nanocrystalline $La_{1-x}Ba_{x}MnO_{3}$ (0 leq x leq 0.3) powders have been synthesized by a low temperature initiated-self propagating, gas producing solution combustion process. The crystal structure and lattice parameters of the powders obtained from X-ray diffraction studies confirm that the as formed powders are cubic in symmetry. On calcination (900 oC, 6 h) Ba-doped powders retain cubic symmetry, whereas the Ba-free $LaMnO_{3}$ transformed to rhombohedral symmetry. It is observed that with increase of Ba concentration in $LaMnO_{3}$ the diffraction peaks move to lower 2q values indicating that the lattice parameters increase with the increase of Ba doping, which may be caused by higher ionic size of $Ba^{2+}$ ion in comparison with $La^{3+}$ ion. This shift confirms the accommodation of $Ba^{2+}$ ion into the lattice structure. The microstructure and particle size of the compounds were examined by scanning electron microscope and it is observed that agglomerated particle size is around 1mm. The crystallite sizes of the doped lanthanum manganites calculated from broadness of the XRD peaks are in the range 30-50 nm. It is obvious that the particle size increases as calcination temperature increases. The $Mn^{4+}$ content present in the samples was determined by iodometric titration as function of Ba doping. Both undoped and doped lanthanum manganites show two active IR vibrational modes at 400 and 600 $cm^{-1}$. The low temperature resistivity measurements down to 77 K, have been carried out by four probe method. The resistivity slightly increases with Ba-content up to x = 0.2 and there after decreases. We observed that the samples studied in the present work show different metal-insulator transition temperature $(T_{M-I})$ from that of single crystalline as well as the samples prepared by ceramic route. All the samples exhibit $T_{M-I}$ in the range 184-228 K and it is interesting to note that, as the Ba-content increases the $T_{M-I}$ shifts to lower temperature side. The maximum $T_{M-I}$ of 228 K was observed for 10% of Ba doping.
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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/00003825/01/1.pdf
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