Improved Thermoelectric Performance of NbCoSb with Intrinsic Nb Vacancies and Ni-Doping-Induced Band Degeneracy

Abstract

Lately, the nominal 19-electron half-Heusler compound NbCoSb, historically viewed as a metal, has attracted reacquaintance and widespread attention because of its unexpected high thermoelectric (TE) performance. Here, the electronic structures of Nb x Co 1−y Ni y Sb (x = 0.8, 1; y = 0, 0.1) have been systematically investigated by using the first-principles method and semiclassical Boltzmann transport theory. We demonstrate that Ni doping at Co sites in NbCoSb with 20% intrinsic Nb vacancies (Nb 0.8 CoSb) leads to a large band degeneracy, and the conduction band edge are mainly provided by the d-orbitals of the Ni, Co, and Nb atoms. The relative localization of the d orbitals not only remarkably increased the density-of-states effective mass near the Fermi energy but also retained a high mobility, which resulted in an optimal electrical conductivity without significant reduction of the Seebeck coefficient (∼−411.08 μV K −1 at 800 K) and thereby a large power factor. Meanwhile, Ni doping still preserved a low lattice thermal conductivity. As a result, a peak zT of 1.18 was achieved at 1100 K in the compound Nb 0.8 Co 0.9 Ni 0.1 Sb with a carrier concentration of 4.35 × 10 20 cm −3 . The present work identifies that Ni doping is an effective method to improve the TE properties of nominally 19-electron NbCoSb compounds with Nb vacancies and demonstrates the great potential for searching of nonstoichiometric 19electron half-Heusler compounds with vacancies.

Target-Induced Photocurrent-Polarity-Switching PEC Sensing Platform Based on In Situ Generation of Oxygen Vacancy-Modulated Energy Band Structures

“…Compared with the loading of new semiconductor materials, the introduction of vacancies to directly modulate the energy band structure of semiconductor materials contributes to the formation of new heterojunctions, which helps to achieve polarization modulation. , On the one side, vacancies can directly and effectively change the energy band structure of semiconductors, construct new energy band matching mechanisms and electron transfer directions effectively, and directly regulate the polarization of the photoelectric interface . On the other side, the introduction of vacancies preserves the original physical contact between the materials, promotes interfacial electron transport, and amplifies the effect of its modulated polarization . In addition, enzyme catalysis may alter the redox conditions at the semiconductor/electrolyte interface, such as the number and type of electron donors and acceptors. – The redox conditions of the PEC system may change under the catalytic action of enzymes, potentially altering the polarity of the photocurrent response.…”

“…19 On the other side, the introduction of vacancies preserves the original physical contact between the materials, promotes interfacial electron transport, and amplifies the effect of its modulated polarization. 20 In addition, enzyme catalysis may alter the redox conditions at the semiconductor/electrolyte interface, such as the number and type of electron donors and acceptors. 21−23 The redox conditions of the PEC system may change under the catalytic action of enzymes, potentially altering the polarity of the photocurrent response.…”

Synergistic Effect of Phonon Localization and Band Convergence in a WSe2–WTe2 Superlattice Leads to High Thermoelectric Performance

“…In the bipolar effect, the σ total and S total from the two types of carriers are calculated from S total = S e σ e + S h σ h σ total σ total = σ e + σ h Here, σ e , S e , σ h , and S h represent the electron electrical conductivity, the electron Seebeck coefficient, hole electrical conductivity, and the hole Seebeck coefficient, respectively. In addition, we have also investigated the variation of S with chemical potential and presented in Figure S6 of the Supporting Information.…”

“…Interestingly, we observe that there is a decrease in S with temperatures for both materials, which could be because of the bipolar conduction effect at higher temperatures. It is a very well-known fact in the literature , that the bipolar effect that occurred due to the thermal excitation of charge carriers becomes more dominating at higher temperatures and leads to a decrease in the Seebeck coefficient at elevated temperatures.…”

“…In the bipolar effect, the σ total and S total from the two types of carriers are calculated from 57…”