Doping Bottleneck in Hematite: Multipole Clustering by Small Polarons
Doping Bottleneck in Hematite: Multipole Clustering by Small Polarons
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DOI：
10.1021/acs.chemmater.1c00304
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发表时间：
2021-06
影响因子：
8.6
通讯作者：
T. Smart;Valentin Urena Baltazar;Mingpeng Chen;Bin Yao;Kiley Mayford;F. Bridges;Yat Li;Y. Ping-Y.-P
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文献类型：
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作者：
T. Smart;Valentin Urena Baltazar;Mingpeng Chen;Bin Yao;Kiley Mayford;F. Bridges;Yat Li;Y. Ping-Y.-P
过渡金属氧化物中的高效掺杂对于从根本上克服由于小极化子形成而导致的低载流子电导率并达到其用于能量转换应用的理想效率至关重要。然而，在诸如赤铁矿的极化离子氧化物中的最佳掺杂浓度非常低，例如小于百分之一，这阻碍了掺杂对于实际应用的益处。在这项工作中，我们通过第一性原理计算研究了IV族（Ti、Zr和Hf）和XIV族（Si、Ge、Sn和Pb）掺杂剂的低最佳掺杂浓度的潜在机制。我们发现，即使在非常低的掺杂剂浓度，新的掺杂剂极化子集群发生，类似于电多极。这些多极子在室温下可以非常稳定，并且与单独的掺杂剂相比难以完全掺杂，因此它们不利于载流子浓度的提高。这使我们能够揭示赤铁矿中掺杂瓶颈的奥秘，并为优化极化氧化物中的掺杂和载流子电导率提供指导，以实现高效的能量转换应用。
Highly effective doping in transition metal oxides is critical to fundamentally overcome low carrier conductivity due to small polaron formation and reach their ideal efficiency for energy conversion applications. However, the optimal doping concentration in polaronic oxides such as hematite has been extremely low, for example, less than a percent, which hinders the benefits of doping for practical applications. In this work, we investigate the underlying mechanism of low optimal doping concentration with group IV (Ti, Zr, and Hf) and XIV (Si, Ge, Sn, and Pb) dopants from first-principles calculations. We find that novel dopant-polaron clustering occurs even at very low dopant concentrations and resembles electric multipoles. These multipoles can be very stable at room temperature and are difficult to fully ionize compared to separate dopants, and thus they are detrimental to carrier concentration improvement. This allows us to uncover mysteries of the doping bottleneck in hematite and provide guidance for optimizing doping and carrier conductivity in polaronic oxides toward highly efficient energy conversion applications.