Chapter 14
A Theoretical Study on Proton Conduction
Mechanism in BaZrO 3 Perovskite
Taku Onishi and Trygve Helgaker
Abstract Hybrid Kohn-Sham calculations were performed to clarify the proton
conduction mechanism in BaZrO 3 perovskite, from the viewpoint of energetics and
bonding. The calculated activation energy for proton conduction was much larger
than the experimental one. It is because O–H covalent bonding formation affects the
low-frequency real part in AC impedance spectra. The higher proton conductivity in
wet condition is derived from “proton pumping effect”. We concluded that N-doping
at oxygen site enhances the proton conductivity, due to the existence of much hydrogen atoms. We also investigated hydrogen defect around zirconium vacancy.
14.1 Introduction
The perovskite-type cubic BaZrO 3 shows proton conductivity in high temperature
range (over 500 K) [1]. Many experimental [2–7] and theoretical [8–12] works were
performed to investigate the proton conduction mechanism. Two proton conduction
paths were theoretically proposed [10–12]. However, our previous studies [13, 14]
discovered that three different proton conduction paths exist in cubic SrTiO 3 perovskite.
Figure 14.1 shows three proton conduction paths in BaZrO 3 perovskite: O–O
diagonal path, two-dimensional O–H rotation within Zr 4 O 4 square, and threedimensional (3D) O–H rotation cross Zr 4 O 4 square. The 3D O–H rotation was
neglected in other previous studies. In general, pure Kohn-Sham methods such as
T. Onishi (B)
Department of Chemistry for Materials, Graduate School of Engineering, Mie University,
1577 Kurimamachiya-cho, Tsu, Mie 517-8507, Japan
e-mail: taku@chem.mie-u.ac.jp
T. Onishi
The Center of Ultimate Technology on Nano-Electronics, Mie University (MIE-CUTE),
1577 Kurimamachiya-cho, Tsu, Mie 517-8507, Japan
T. Onishi
The Centre for Theoretical and Computational Chemistry (CTCC), Department of Chemistry,
University of Oslo, Postbox 1033, Blindern 0315 Oslo, Norway
e-mail: taku.onishi@kjemi.uio.no
M. Hotokka et al. (eds.), Advances in Quantum Methods and Applications in
Chemistry, Physics, and Biology, Progress in Theoretical Chemistry and Physics 27,
DOI 10.1007/978-3-319-01529-3_14,
© Springer International Publishing Switzerland 2013
233
A Theoretical Study on Proton Conduction
Mechanism in BaZrO 3 Perovskite
Taku Onishi and Trygve Helgaker
Abstract Hybrid Kohn-Sham calculations were performed to clarify the proton
conduction mechanism in BaZrO 3 perovskite, from the viewpoint of energetics and
bonding. The calculated activation energy for proton conduction was much larger
than the experimental one. It is because O–H covalent bonding formation affects the
low-frequency real part in AC impedance spectra. The higher proton conductivity in
wet condition is derived from “proton pumping effect”. We concluded that N-doping
at oxygen site enhances the proton conductivity, due to the existence of much hydrogen atoms. We also investigated hydrogen defect around zirconium vacancy.
14.1 Introduction
The perovskite-type cubic BaZrO 3 shows proton conductivity in high temperature
range (over 500 K) [1]. Many experimental [2–7] and theoretical [8–12] works were
performed to investigate the proton conduction mechanism. Two proton conduction
paths were theoretically proposed [10–12]. However, our previous studies [13, 14]
discovered that three different proton conduction paths exist in cubic SrTiO 3 perovskite.
Figure 14.1 shows three proton conduction paths in BaZrO 3 perovskite: O–O
diagonal path, two-dimensional O–H rotation within Zr 4 O 4 square, and threedimensional (3D) O–H rotation cross Zr 4 O 4 square. The 3D O–H rotation was
neglected in other previous studies. In general, pure Kohn-Sham methods such as
T. Onishi (B)
Department of Chemistry for Materials, Graduate School of Engineering, Mie University,
1577 Kurimamachiya-cho, Tsu, Mie 517-8507, Japan
e-mail: taku@chem.mie-u.ac.jp
T. Onishi
The Center of Ultimate Technology on Nano-Electronics, Mie University (MIE-CUTE),
1577 Kurimamachiya-cho, Tsu, Mie 517-8507, Japan
T. Onishi
The Centre for Theoretical and Computational Chemistry (CTCC), Department of Chemistry,
University of Oslo, Postbox 1033, Blindern 0315 Oslo, Norway
e-mail: taku.onishi@kjemi.uio.no
M. Hotokka et al. (eds.), Advances in Quantum Methods and Applications in
Chemistry, Physics, and Biology, Progress in Theoretical Chemistry and Physics 27,
DOI 10.1007/978-3-319-01529-3_14,
© Springer International Publishing Switzerland 2013
233