Transition metal oxides (TMOs) have been the most promising candidates for energy conversion and storage applications, such as solar-to-fuel conversion and Li-ion batteries. However, their efficiency has been fundamentally limited by their poor electronic conductivities, mainly due to the strong electron-phonon interactions that cause trapping of free electrons or holes by the local lattice distortion and forming so-called “small polarons”. These small polarons conduct through thermally activated hopping between lattice sites instead of intra-band conduction.<br/><br/>In this talk, we developed a theoretical framework based on Landau-Zener theory extended to non-adiabatic electron transfer, coupled with random walk simulations to obtain the small polaron mobility of pristine and doped TMOs[1]. We found certain dopants that have “repulsive interactions” with polarons can lower the hopping barriers and improve the polaron hopping mobility in TMOs such as Mo and W in BiVO<sub>4</sub>. Interestingly, in magnetic oxides such as CuO, “spin polaron” can form and conduct through spin-flipped hopping conduction[2]. In this case, doping with non-magnetic shallow impurities can further improve the hopping mobility by breaking the magnetic coupling and lower the hopping barriers. Our work shines light on overcoming fundamental limitation of poor electronic conduction in TMOs.

Effects of defects on electron polaron formation and transport in transition metal oxides

2019 Spring National Meeting

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