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.

中文翻译：

---

间隙 Ni 的全壳层 d 轨道和基于 Ni 的半 Heusler 热电半导体中的异常电传输


我们系统地研究了 Ni 基半 Heusler XNi1+xZ 半导体中额外间隙 Nii 的全壳层 d10 轨道诱导的异常电子特性和电传输。来自间隙 Nii 的轨道具有独特的 d10 构型，在八面体晶体场下分为高能 eg4 轨道和低能 t2g6 轨道。在 XIVNi1+xZIV （XIV=Ti， Zr， Hf;ZIV=Sn， Pb），定位的 Nii-eg4 状态落在内禀带隙内，导致带隙减小。在 XIIINi1+xZV （XIII=Sc， Y;ZV=Sb， Bi），Nii-eg4 态与本征价带重叠。此外，间隙 Nii 扰乱了最近邻 X 原子配位，导致简并导带最小值的分裂，这在 XIIINi1+xZV 中比 XIVNi1+xZIV 更强。微量的间质 Nii 显着影响电传输特性。额外间隙 Nii 的引入降低了态密度、有效质量、电子群速度和弛豫时间，导致塞贝克系数和中低温下的电导率降低。然而，在带隙中引入局部 Nii-eg4 态作为新的价带最大值，在低载流子浓度区间减弱了高温双极效应，从而在高温下保持高热功率。此外，通过 XIVNi1+xZIV 和 XIIINi1+xZV 的固溶体对 Nii-d10 轨道的调谐有望进一步优化电输运。