RESUMO
In electrochemical devices, it is important to control the ionic transport between the electrodes and solid electrolytes. However, it is difficult to tune the transport without applying an electric field. This paper presents a method to modulate the transport via tuning of the electrochemical potential difference by controlling the electronic states at the interfaces. We fabricated thin-film solid-state Li batteries using LiTi2O4 thin films as positive electrodes. The spontaneous Li-ion transport between the solid electrolyte and LiTi2O4 is controlled by tuning the electrochemical potential difference via use of an electrically conducting Nb-doped SrTiO3 substrate. This study establishes the foundation for rectifying the ionic transport via electronic energy band alignment.
RESUMO
Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30-70 K in pressure range of 100-170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50-70 K in pressure range of 100-150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system.