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Effect of the sintering temperature on the properties of nanocrystalline Ca1−x Sm x MnO3 (0≤ x ≤0.4) powders

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Title: Effect of the sintering temperature on the properties of nanocrystalline Ca1−x Sm x MnO3 (0≤ x ≤0.4) powders
Authors: Matos, I.1, Sério, S.2, Lopes, M.E.3, Nunes, M.R.4, Jorge, M.E. Melo4 mdjorge@fc.ul.pt
Source: Journal of Alloys & Compounds. Oct2011, Vol. 509 Issue 40, p9617-9626. 10p.
Subjects: Sintering, Temperature effect, Nanocrystals, Annealing of metals, Crystal growth, Phase transitions, Semiconductors, Chemical bonds, Rietveld refinement, Electric properties of metals
Abstract: Abstract: Nanocrystalline Ca1−x Sm x MnO3 (0≤ x ≤0.4) manganites were prepared by a soft chemical method (Pechini method) followed by auto-combustion and sintering in air at 1073 or 1473K. Single-phase powders with general composition Ca1−x Sm x MnO3 were obtained after 18h annealing. The particle and grain sizes of the substituted Sm-manganites did not exhibit variation with samarium content, but increase with increasing the sintering temperature. All manganites show two active IR vibrational modes near 400 and 600cm−1 characteristic of the BO6 octahedron vibrations. For the samples sintered at T s =1473K, the partial substitution of calcium by samarium in the CaMnO3 phase induces a marked decrease in the electrical resistivity, in the temperature range of 300–900K, and at the same time a metal-to-insulator transition occurs; for T s =1073K all the samples present semiconductor behaviour. With the increase of the annealing temperature the grain size increases and a metal–semiconductor transition appears. The results can be ascribed to the Mn4+/Mn3+ ratio and particle grain size. The effects of particle size on the electrical properties can be attributed to the domain status, changes in the Mn–O–Mn bond angle and Mn–O bond length. [Copyright &y& Elsevier]
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Database: Engineering Source
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Abstract:Abstract: Nanocrystalline Ca1−x Sm x MnO3 (0≤ x ≤0.4) manganites were prepared by a soft chemical method (Pechini method) followed by auto-combustion and sintering in air at 1073 or 1473K. Single-phase powders with general composition Ca1−x Sm x MnO3 were obtained after 18h annealing. The particle and grain sizes of the substituted Sm-manganites did not exhibit variation with samarium content, but increase with increasing the sintering temperature. All manganites show two active IR vibrational modes near 400 and 600cm−1 characteristic of the BO6 octahedron vibrations. For the samples sintered at T s =1473K, the partial substitution of calcium by samarium in the CaMnO3 phase induces a marked decrease in the electrical resistivity, in the temperature range of 300–900K, and at the same time a metal-to-insulator transition occurs; for T s =1073K all the samples present semiconductor behaviour. With the increase of the annealing temperature the grain size increases and a metal–semiconductor transition appears. The results can be ascribed to the Mn4+/Mn3+ ratio and particle grain size. The effects of particle size on the electrical properties can be attributed to the domain status, changes in the Mn–O–Mn bond angle and Mn–O bond length. [Copyright &y& Elsevier]
ISSN:09258388
DOI:10.1016/j.jallcom.2011.07.032