TY - JOUR
T1 - Effect of Ba substitution on structural, electrical and thermal properties of La0.65Ca0.35-xBaxMnO3(0 ≤ x ≤ 0.25) manganites
AU - Manjunatha, S. O.
AU - Rao, Ashok
AU - Lin, T. Y.
AU - Chang, C. M.
AU - Kuo, Y. K.
N1 - Funding Information:
One of the authors (M.S.O) acknowledges Manipal University for providing the financial support to pursue Ph.D. We thank Dr. Shivakumara C, Solid State and Structural Chemistry Unit, IISc, Bangalore, for providing necessary help in XRD analysis. Authors are grateful to Material processing laboratory, NITK, Surathkal for providing density and hardness measurement facilities. The authors are thankful to Dr. Rajeev Rawat and Mr. Sachin Kumar, UGC-DAE, CSR Indore for resistivity and MR measurement. The transport and thermal measurements are supported by the Ministry of Science and Technology of Taiwan under Grant No. MOST 103-2112-M-259-008-MY3 (Y.K.K.).
Publisher Copyright:
© 2014 Elsevier B.V. All rights reserved.
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2015/1/15
Y1 - 2015/1/15
N2 - In the present communication, the effect of Ba substitution on the structural, mechanical, electrical transport and thermal properties of La0.65Ca0.35-xBaxMnO3(0.00 ≤ x ≤ 0.25) manganites have been investigated. Rietveld refinement of XRD data reveals that all samples are single phase. With increasing Ba content, a transformation of crystal structure from rhombohedral (x = 0.00-0.15) to cubic symmetry (x = 0.25) is observed. In the micro-hardness study, a correlation between the average grain size and micro-hardness is concluded. It is found that all samples exhibit a clear metal-insulator transition, and the transition temperature (TMI) shifts monotonically towards higher temperature. The Seebeck coefficient (S) of the pristine sample is negative in the entire temperature range, whereas for all doped samples the measured S exhibits a crossover from positive to negative values. The analysis of Seebeck coefficient data indicates that the small polaron hopping model is operative in the high temperature region. The room-temperature magnitude of thermal conductivity, κ of the studied samples is in the range of 20-35 mW/cm K and such low value is presumably attributed to the Jahn Teller (J-T) effect. An analysis of κ using Wiedemann-Franz's (W-F) law confirms that the total thermal conductivity is mainly associated with the lattice phonons rather than charge carriers. The change in entropy associated with the transition evaluated from the specific heat measurements is found to decrease with increasing x, most likely due to the enhancement of magnetic inhomogeneity in these manganites.
AB - In the present communication, the effect of Ba substitution on the structural, mechanical, electrical transport and thermal properties of La0.65Ca0.35-xBaxMnO3(0.00 ≤ x ≤ 0.25) manganites have been investigated. Rietveld refinement of XRD data reveals that all samples are single phase. With increasing Ba content, a transformation of crystal structure from rhombohedral (x = 0.00-0.15) to cubic symmetry (x = 0.25) is observed. In the micro-hardness study, a correlation between the average grain size and micro-hardness is concluded. It is found that all samples exhibit a clear metal-insulator transition, and the transition temperature (TMI) shifts monotonically towards higher temperature. The Seebeck coefficient (S) of the pristine sample is negative in the entire temperature range, whereas for all doped samples the measured S exhibits a crossover from positive to negative values. The analysis of Seebeck coefficient data indicates that the small polaron hopping model is operative in the high temperature region. The room-temperature magnitude of thermal conductivity, κ of the studied samples is in the range of 20-35 mW/cm K and such low value is presumably attributed to the Jahn Teller (J-T) effect. An analysis of κ using Wiedemann-Franz's (W-F) law confirms that the total thermal conductivity is mainly associated with the lattice phonons rather than charge carriers. The change in entropy associated with the transition evaluated from the specific heat measurements is found to decrease with increasing x, most likely due to the enhancement of magnetic inhomogeneity in these manganites.
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U2 - 10.1016/j.jallcom.2014.09.042
DO - 10.1016/j.jallcom.2014.09.042
M3 - Article
AN - SCOPUS:84907572359
SN - 0925-8388
VL - 619
SP - 303
EP - 310
JO - Journal of Alloys and Compounds
JF - Journal of Alloys and Compounds
ER -