Hematite (α-Fe₂O₃) is a promising and Earth-abundant material for solar fuel production, and Si-doping has been employed as a general strategy to improve its performance. However, an atomistic description that reconciles the modifications that Si-doping induces on the morphology, crystalline lattice, and electronic and magnetic properties of α-Fe₂O₃ has remained elusive. Here we report on the role of electron small polarons in driving the morphological transition from nearly rounded-shaped to nanowire nanocrystals in Si-doped hematite α-Fe₂O₃. Electron small polaron formation is evidenced by the formation of Fe²⁺ and the increase of FeO₆ distortion at increasing Si content. Local analysis via pair distribution function highlights an unreported crossover from small to large polarons, which affects the correlation length of the polaronic distortion from short to average scales. Ferromagnetic double exchange interactions between Fe²⁺/Fe³⁺ species are found to be the driving force of the crossover, constraining the chaining of chemical bonds along the [110] crystallographic direction. This promotes the increase in the reticular density of Fe atoms along the hematite basal plane only, which boosts the anisotropic growth of nanocrystals with more extended [110] facets. Our results show that magnetic and electronic interactions drive preferential crystallographic growth in Si-doped α-Fe₂O₃, thus providing new insights for the nanoscale structural design of efficient solar fuel devices.

中文翻译：

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电子小极化子和磁相互作用直接各向异性生长硅掺杂的赤铁矿纳米晶体

赤铁矿（α-的Fe ₂ ö ₃）为太阳能燃料生产有希望的和地球丰富材料，及Si掺杂已被用作以提高其性能的通用策略。然而，原子论描述该调和修改的Si掺杂的形态，晶格，和的α-Fe的电子和磁性能诱导₂ ö ₃一直难以实现。在这里，我们在从驱动形态过渡上的电子小极化子的作用的报告近圆形形的，以纳米线的纳米晶体中掺杂Si的赤铁矿的α-Fe ₂ ö ₃。Fe ²⁺的形成和FeO ₆的增加证明了电子小极化子的形成Si含量增加时的形变。通过对分布函数进行的局部分析突出显示了从小极化子到大极化子的未报告交叉，这影响了极化子畸变从短到平均尺度的相关长度。发现Fe ²⁺ / Fe ³⁺物种之间的铁磁双交换相互作用是交叉的驱动力，从而限制了沿[110]晶体学方向的化学键链。这仅会促进沿赤铁矿基面的铁原子网状密度的增加，从而促进具有更多[110]晶面的纳米晶体的各向异性生长。我们的研究结果表明，磁性和电子相互作用推动择优晶体生长Si掺杂的α-Fe ₂ ö_参见图3，从而为有效的太阳能燃料装置的纳米级结构设计提供了新的见解。