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Title: Effect of the sintering temperature on the properties of nanocrystalline Ca1−xSmxMnO3 (0 ≤ x ≤ 0.4) powders
Authors: Lopes, M E
Melo Jorge, M. E.
Sério, S.
Nunes, M. R.
Matos, I.
Keywords: Nanocrystalline manganites
Samarium substituted
Citrate gel method
Rietveld analysis
Electrical properties
Issue Date: 6-Oct-2011
Publisher: Elsevier
Abstract: Nanocrystalline Ca1−xSmxMnO3 (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 1473 K. Single-phase powders with general composition Ca1−xSmxMnO3 were obtained after 18 h 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 600 cm−1 characteristic of the BO6 octahedron vibrations. For the samples sintered at Ts = 1473 K, the partial substitution of calcium by samarium in the CaMnO3 phase induces a marked decrease in the electrical resistivity, in the temperature range of 300–900 K, and at the same time a metal-to-insulator transition occurs; for Ts = 1073 K 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.
Type: article
Appears in Collections:CQE - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica

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