Proton Channels along Oxygen Octahedral Chains in La3NbO7 - The

Article pubs.acs.org/JPCC

Proton Channels along Oxygen Octahedral Chains in La3NbO7 Kunitada Kato,† Kazuaki Toyoura,*,† Atsutomo Nakamura,† and Katsuyuki Matsunaga†,‡ †

Department of Materials Science and Engineering, Nagoya University, Furo, Chikusa, Nagoya 464-8603, Japan Nanostructures Research Laboratory, Japan Fine Ceramics Center, Atsuta, Nagoya 456-8587, Japan

‡

S Supporting Information *

ABSTRACT: The proton conduction behavior in La3NbO7 is theoretically analyzed by first-principles calculations with the aid of the nudged elastic band method and the kinetic Monte Carlo method. Protons in the crystal migrate over a long range through fast conduction channels along the single NbO6 octahedral chains in the a-axis direction, whose calculated potential barrier is 0.54 eV. The bridging paths connecting the proton channels in the b- and c-axes directions have a higher potential barrier, 0.64 eV, leading to anisotropic proton diffusivity and conductivity, particularly at low temperatures. The preferential bonding of protons to several specific oxide ions is strongly related to the lower potential barrier in the a-axis direction in addition to the presence of the infinite NbO6 chains.

1. INTRODUCTION Acceptor-doped lanthanum niobates, LaNbO4 and La3NbO7, are reported to exhibit predominant proton conductivity at moderate or low temperatures (