A series of Ba1_xEuxTiO3_d (0.1 < x < 0.9) phases with B40 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 B5 unit cells) deviations from the cubic structure model (Pm%3m) were detected by evaluation of the pair distribution function (PDF). These deviations cannot be explained by a simple symmetry breaking model like in EuTiO3_d. The best fit was achieved in the space group Amm2 allowing for a movement of Ti and Ba/Eu along h110i of the parent unit cell as observed for BaTiO3. Density functional calculations delivered an insight into the electronic structure of Ba1_xEuxTiO3_d. 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 o T o 1123 K) the conduction mechanism of Ba1_xEuxTiO3_d (0.1 r x r 0.9) is a polaron hopping when 0 o x r 0.6 and is a thermally activated process when 0.6 o x o 1. Besides, the thermal conduc tivity increases with increasing Eu2+ concentration. Due to a remarkable improvement of the power factor, Ba0.1Eu0.9TiO3_d showed a ZT value of 0.24 at 1123 K.
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, A. Weidenkaff. - In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS. - ISSN 1463-9076. - 19:21(2017 Jun 07), pp. 13469-13480.
Tailoring the structure and thermoelectric properties of BaTiO3via Eu2+ substitution
M. Scavini;S. Checchia;
2017
Abstract
A series of Ba1_xEuxTiO3_d (0.1 < x < 0.9) phases with B40 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 B5 unit cells) deviations from the cubic structure model (Pm%3m) were detected by evaluation of the pair distribution function (PDF). These deviations cannot be explained by a simple symmetry breaking model like in EuTiO3_d. The best fit was achieved in the space group Amm2 allowing for a movement of Ti and Ba/Eu along h110i of the parent unit cell as observed for BaTiO3. Density functional calculations delivered an insight into the electronic structure of Ba1_xEuxTiO3_d. 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 o T o 1123 K) the conduction mechanism of Ba1_xEuxTiO3_d (0.1 r x r 0.9) is a polaron hopping when 0 o x r 0.6 and is a thermally activated process when 0.6 o x o 1. Besides, the thermal conduc tivity increases with increasing Eu2+ concentration. Due to a remarkable improvement of the power factor, Ba0.1Eu0.9TiO3_d showed a ZT value of 0.24 at 1123 K.File | Dimensione | Formato | |
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