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Tailoring the structure and thermoelectric properties of BaTiO3 via Eu2+ substitution

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Abstract

A series of Ba1−xEuxTiO3−δ (0.1 ≤ x ≤ 0.9) phases with ∼40 nm particle size were synthesized via a Pechini method followed by annealing and sintering under a reducing atmosphere. The effects of Eu2+ substitution on the BaTiO3 crystal structure and the thermoelectric transport properties were systematically investigated. According to synchrotron X-ray diffraction data only cubic perovskite structures were observed. On the local scale below about 20 Å (equal to ∼5 unit cells) deviations from the cubic structure model (Pm[3 with combining macron]m) were detected by evaluation of the pair distribution function (PDF). These deviations cannot be explained by a simple symmetry breaking model like in EuTiO3−δ. The best fit was achieved in the space group Amm2 allowing for a movement of Ti and Ba/Eu along 〈110〉 of the parent unit cell as observed for BaTiO3. Density functional calculations delivered an insight into the electronic structure of Ba1−xEuxTiO3−δ. From the obtained density of states a significant reduction of the band gap by the presence of filled Eu2+ 4f states at the top of the valence band was observed. The physical property measurements revealed that barium–europium titanates exhibit n-type semiconducting behavior and at high temperature the electrical conductivity strongly depended on the Eu2+ content. Activation energies calculated from the electrical conductivity and Seebeck coefficient data indicate that at high temperatures (800 K < T < 1123 K) the conduction mechanism of Ba1−xEuxTiO3−δ (0.1 ≤ x ≤ 0.9) is a polaron hopping when 0 < x ≤ 0.6 and is a thermally activated process when 0.6 < x < 1. Besides, the thermal conductivity increases with increasing Eu2+ concentration. Due to a remarkable improvement of the power factor, Ba0.1Eu0.9TiO3−δ showed a ZT value of 0.24 at 1123 K.

Graphical abstract: Tailoring the structure and thermoelectric properties of BaTiO3 via Eu2+ substitution

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Publication details

The article was received on 02 Jan 2017, accepted on 05 Mar 2017 and first published on 09 Mar 2017


Article type: Paper
DOI: 10.1039/C7CP00020K
Citation: Phys. Chem. Chem. Phys., 2017, Advance Article
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    Tailoring the structure and thermoelectric properties of BaTiO3 via Eu2+ substitution

    X. Xiao, M. Widenmeyer, W. Xie, T. Zou, S. Yoon, M. Scavini, S. Checchia, Z. Zhong, P. Hansmann, S. Kilper, A. Kovalevsky and A. Weidenkaff, Phys. Chem. Chem. Phys., 2017, Advance Article , DOI: 10.1039/C7CP00020K

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