Yurong Ruan , Tao Feng , Ke Zhong , Bing Wen , Wenqing Zhang
{"title":"Full-shell d-orbitals of interstitial Ni and anomalous electrical transport in Ni-based half-Heusler thermoelectric semiconductors","authors":"Yurong Ruan , Tao Feng , Ke Zhong , Bing Wen , Wenqing Zhang","doi":"10.1016/j.mtphys.2024.101558","DOIUrl":null,"url":null,"abstract":"<div><div>We systematically investigate the anomalous electronic properties and electrical transport induced by full-shell <em>d</em><sup>10</sup>-orbitals of the extra interstitial Ni<sub><em>i</em></sub> in Ni-based half-Heusler XNi<sub>1+<em>x</em></sub>Z semiconductors. The orbitals from the interstitial Ni<sub><em>i</em></sub> have the unique <em>d</em><sup>10</sup> configuration, split into high-energy <em>e</em><sub><em>g</em></sub><sup>4</sup> orbitals and low-energy <em>t</em><sub><em>2g</em></sub><sup>6</sup> orbitals under the octahedral crystal field. In X<sup>IV</sup>Ni<sub>1+<em>x</em></sub>Z<sup>IV</sup> (X<sup>IV</sup>=Ti, Zr, Hf; Z<sup>IV</sup>=Sn, Pb), the localized Ni<sub><em>i</em></sub>-<em>e</em><sub><em>g</em></sub><sup>4</sup> states fall within the intrinsic bandgap leading to a reduced bandgap. In X<sup>III</sup>Ni<sub>1+<em>x</em></sub>Z<sup>V</sup> (X<sup>III</sup>=Sc, Y; Z<sup>V</sup>=Sb, Bi), the Ni<sub><em>i</em></sub>-<em>e</em><sub><em>g</em></sub><sup>4</sup> states overlap with the intrinsic valence bands. Additionally, the interstitial Ni<sub><em>i</em></sub> perturb the nearest neighbor X atomic coordination, leading to the splitting of degenerate conduction band minimum, which is stronger in X<sup>III</sup>Ni<sub>1+<em>x</em></sub>Z<sup>V</sup> than X<sup>IV</sup>Ni<sub>1+<em>x</em></sub>Z<sup>IV</sup>. Trace amounts of interstitial Ni<sub><em>i</em></sub> significantly impact the electrical transport properties. The introduction of the extra interstitial Ni<sub><em>i</em></sub> 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 Ni<sub><em>i</em></sub>-<em>e</em><sub><em>g</em></sub><sup>4</sup> 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 Ni<sub><em>i</em></sub>-<em>d</em><sup>10</sup> orbitals by solid solution of both X<sup>IV</sup>Ni<sub>1+<em>x</em></sub>Z<sup>IV</sup> and X<sup>III</sup>Ni<sub>1+<em>x</em></sub>Z<sup>V</sup> is expected to further optimize the electrical transport.</div></div>","PeriodicalId":18253,"journal":{"name":"Materials Today Physics","volume":null,"pages":null},"PeriodicalIF":10.0000,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Materials Today Physics","FirstCategoryId":"88","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S2542529324002347","RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"MATERIALS SCIENCE, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
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.
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.