The proton conduction behavior in La 3 NbO 7 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 NbO 6 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 NbO 6 chains.

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