Issue 21, 2017

Tailoring the structure and thermoelectric properties of BaTiO3via Eu2+ substitution

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 BaTiO3via Eu2+ substitution

Supplementary files

Article information

Article type
Paper
Submitted
02 Jan 2017
Accepted
05 Mar 2017
First published
09 Mar 2017

Phys. Chem. Chem. Phys., 2017,19, 13469-13480

Tailoring the structure and thermoelectric properties of BaTiO3via 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, 19, 13469 DOI: 10.1039/C7CP00020K

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