Full-shell d-orbitals of interstitial Ni and anomalous electrical transport in Ni-based half-Heusler thermoelectric semiconductors

IF 10 2区 材料科学 Q1 MATERIALS SCIENCE, MULTIDISCIPLINARY Materials Today Physics Pub Date : 2024-09-21 DOI:10.1016/j.mtphys.2024.101558
Yurong Ruan , Tao Feng , Ke Zhong , Bing Wen , Wenqing Zhang
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Abstract

We systematically investigate the anomalous electronic properties and electrical transport induced by full-shell d10-orbitals of the extra interstitial Nii in Ni-based half-Heusler XNi1+xZ semiconductors. The orbitals from the interstitial Nii have the unique d10 configuration, split into high-energy eg4 orbitals and low-energy t2g6 orbitals under the octahedral crystal field. In XIVNi1+xZIV (XIV=Ti, Zr, Hf; ZIV=Sn, Pb), the localized Nii-eg4 states fall within the intrinsic bandgap leading to a reduced bandgap. In XIIINi1+xZV (XIII=Sc, Y; ZV=Sb, Bi), the Nii-eg4 states overlap with the intrinsic valence bands. Additionally, the interstitial Nii perturb the nearest neighbor X atomic coordination, leading to the splitting of degenerate conduction band minimum, which is stronger in XIIINi1+xZV than XIVNi1+xZIV. Trace amounts of interstitial Nii significantly impact the electrical transport properties. The introduction of the extra interstitial Nii reduces the density of states effective mass, the electron group velocity, and the relaxation time, leading to a decrease of the Seebeck coefficient and electrical conductivity at low and medium temperatures. Nevertheless, the introduction of localized Nii-eg4 states within the bandgap as new valence band maximum attenuate the high-temperature bipolar effect at low carrier concentration intervals, thus maintaining a high thermopower at elevated temperatures. Furthermore, the tuning of the Nii-d10 orbitals by solid solution of both XIVNi1+xZIV and XIIINi1+xZV is expected to further optimize the electrical transport.
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镍基半休斯勒热电半导体中间隙镍的全壳 d 轨道和反常电输运
我们系统地研究了镍基半休斯勒 XNi1+xZ 半导体中额外间隙 Nii 的全壳 d10 轨道诱导的异常电子特性和电输运。间隙 Nii 的轨道具有独特的 d10 构型,在八面体晶场下分为高能 eg4 轨道和低能 t2g6 轨道。在 XIVNi1+xZIV (XIV=钛、锆、铪;ZIV=硒、铅)中,局部 Nii-eg4 态落在本征带隙内,导致带隙减小。在 XIIINi1+xZV (XIII=Sc、Y;ZV=Sb、Bi)中,Nii-eg4 态与本征价带重叠。此外,间隙 Nii 会扰动近邻 X 原子的配位,导致退行导带最小值的分裂,XIIINi1+xZV 中的分裂比 XIVNi1+xZIV 中的更强。微量的间隙 Nii 会显著影响电传输特性。引入额外的间隙 Nii 会降低态密度的有效质量、电子群速度和弛豫时间,从而导致低温和中温下的塞贝克系数和电导率下降。不过,在带隙内引入局部 Nii-eg4 态作为新的价带最大值,可以减弱低载流子浓度区间的高温双极效应,从而在高温下保持较高的热功率。此外,通过固溶 XIVNi1+xZIV 和 XIIINi1+xZV 来调整 Nii-d10 轨道,有望进一步优化电传输。
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来源期刊
Materials Today Physics
Materials Today Physics Materials Science-General Materials Science
CiteScore
14.00
自引率
7.80%
发文量
284
审稿时长
15 days
期刊介绍: Materials Today Physics is a multi-disciplinary journal focused on the physics of materials, encompassing both the physical properties and materials synthesis. Operating at the interface of physics and materials science, this journal covers one of the largest and most dynamic fields within physical science. The forefront research in materials physics is driving advancements in new materials, uncovering new physics, and fostering novel applications at an unprecedented pace.
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