Low Phonon Group Velocities Research Articles

Ultralow lattice thermal conductivity in K2AuBi and its thermoelectric properties

Thermoelectric materials are best known for their prowess to transform the environment’s waste heat into electricity. In an endeavor to explore new thermoelectric prospects, in the present study, we investigate K2AuBi using density functional theory-based first-principles simulations. From our simulations, we find an intrinsically low lattice thermal conductivity of 0.43 W m−1 K−1 at 300 K in K2AuBi. Based on our detailed analysis, we find the reasons for such a low value of lattice thermal conductivity as, low phonon group velocities, short phonon lifetimes, anharmonicity in the lattice vibrations, and significant mean square displacements of K and Au atoms. The large mean square displacements hint at weak bonding and anharmonicity in the lattice vibrations, favoring more phonons scattering. We also find that the vibrations of K-atoms can be related to rattlers, conducive to low lattice thermal conductivity. Our simulations predict a high value, ∼784 μV K−1, of Seebeck coefficient at 700 K on account of the large density of states in the vicinity of Fermi level. Combining our computed lattice thermal conductivity with electrical transport properties, we obtain a high figure of merit, ZT∼ 1.04, at 700 K in K2AuBi.

Ultralow thermal conductivity and high thermoelectric performance induced by dimensionality reduction in chain-like compounds X2PtSe2 (X=K, rb)

Balancing low lattice thermal conductivity (κL) with a high power factor is a major challenge in the research of thermoelectric (TE) materials. In this paper, we report on a class of chain-like compounds, X2PtSe2(X = K, Rb), characterized by strong lattice anharmonicity, weak bonds, and low phonon group velocities. Using first-principles calculations in conjunction with self-consistent phonon theory and the Boltzmann transport equation, we systematically investigate the thermal and electrical transport properties of X2PtSe2(X = K, Rb). At room temperature, the κL of K2PtSe2 and Rb2PtSe2 in the direction perpendicular to the Pt–Se chains is only 0.15 and 0.10 Wm−1K−1, respectively. Additionally, due to the low-dimensional nature of the Pt–Se chains, these compounds exhibit a ‘pudding-mold type’ band structure, contributing to a TE power factor. At 300K, under n-type doping, K2PtSe2 and Rb2PtSe2 achieve TE figures of merit (ZT) values of 1.66 and 1.67, respectively, in the direction perpendicular to the Pt–Se chains. At 500K, the ZT value of Rb2PtSe2 approaches 4, far surpassing traditional TE materials. These results indicate that the chain-like compounds X2PtSe2(X = K, Rb) exhibit excellent TE performance, achieving energy conversion efficiencies comparable to commercial transducer devices.

High‐Performance CaMg2Bi2‐Based Thermoelectric Materials Driven by Lattice Softening and Orbital Alignment via Cadmium Doping

AbstractZintl compounds such as n‐type Mg3(Sb,Bi)2 show promising thermoelectric applications benefiting from their high valley degeneracy and low lattice thermal conductivity. However, the heavier p‐type AMg2X2 (A = Ca, and Yb; X = Bi and Sb) Zintl counterparts even exhibit a higher κlat due to strong chemical bonding. Reducing κlat of AMg2X2 is an important route for improving thermoelectric performance. Herein, it is found that Cd doping at the Mg site in CaMg2Bi2 can weaken intralayer covalent bonds and soften acoustic phonons, as well as fill the optical phonon gap. These effects result in large atomic displacement, low phonon group velocity, and strong lattice vibration anharmonicity. Doping 10% Cd leads to a reduction of 56% in the κlat of CaMg2Bi2. Moreover, Cd doping promotes orbital alignment and thus increases the density‐of‐states effective mass and Seebeck coefficient. Eventually, in conjunction with carrier concentration optimization by Na doping and band structure engineering by Ba doping, a high ZT of ≈1.3 at 873 K in (Ca0.85Ba0.15)0.995Na0.005Mg1.85Cd0.15Bi2 sample is realized. This work highlights the significant role of manipulating chemical bonding in suppressing phonon propagation of semiconductors.

High-throughput screening of potentially ductile and low thermal conductivity ABX3 (X = S, Se, Te) thermoelectric perovskites

Chalcogenide perovskites, renowned for their low lattice thermal conductivity, have emerged as promising candidates for thermoelectric applications. Hence, we leveraged first-principles high-throughput calculations to investigate the electrical and thermal transport properties, as well as the ductility, of the chalcogenide perovskites ABX3 (X = S, Se, Te). Candidates with 30 combinations were initially screened by bandgap screening (Eg > 0.1 eV), stability assessment (Born–Huang criterion), and ductility evaluation (Pugh's ratio: G/K < 0.571, the ratio of shear modulus G to bulk modulus K) from the MatHub-3d database (176 ABX3 crystal structures, 32 kinds of space groups, and number of atoms Natom < 40). Intriguingly, weaker chemical bonding between the A and X site atom pairs gives rise to a higher ductility in the screened quasi-ductile perovskites. Furthermore, it should be noted that the low phonon group velocities confirmed the low lattice thermal conductivity of the materials. In consequence, the identification of quasi-ductile thermoelectrics, characterized by six n-type and six p-type candidates with ZT > 0.3 at 300 K, stands as the most promising candidates for application in thermoelectrics.

Intrinsic ultralow lattice thermal conductivity in lead-free halide perovskites Cs3Bi2X9 (X = Br, I).

Lead-free halide perovskites have recently garnered significant attention due to their rich structural diversity and exceptionally ultralow lattice thermal conductivity (κL). Here, we employ first-principles calculations in conjunction with self-consistent phonon theory and Boltzmann transport equations to investigate the crystal structure, electronic structure, mechanical properties, and κLs of two typical vacancy-ordered halide perovskites, denoted with the general formula Cs3Bi2X9 (X = Br, I). Ultralow κLs of 0.401 and 0.262 W mK-1 at 300 K are predicted for Cs3Bi2Br9 and Cs3Bi2I9, respectively. Our findings reveal that the ultralow κLs are mainly associated with the Cs rattling-like motion, vibrations of halide polyhedral frameworks, and strong scattering in the acoustic and low-frequency optical phonon branches. The structural analysis indicates that these phonon dynamic properties are closely relevant to the bonding hierarchy. The presence of the extended Bi-X antibonding states at the valence band maximum contributes to the soft elastic lattice and low phonon group velocities. Compared to Cs3Bi2Br9, the face-sharing feature and weaker bond strength in Cs3Bi2I9 lead to a softer elasticity modulus and stronger anharmonicity. Additionally, we demonstrate the presence of wave-like κC in Cs3Bi2X9 by evaluating the coherent contribution. Our work provides the physical microscopic mechanisms of the wave-like κC in two typical lead-free halide perovskites, which are beneficial to designing intrinsic materials with the feature of ultralow κL.

Charge-balanced codoping enables exceeding doping limit and ultralow thermal conductivity

Materials with low thermal conductivity are applied extensively in energy management, and breaking the amorphous limits of thermal conductivity to solids has attracted widespread attention from scientists. Doping is a common strategy for achieving low thermal conductivity that can offer abundant scattering centers in which heavier dopants always result in lower phonon group velocities and lower thermal conductivities. However, the amount of equivalent heavy-atom single dopant available is limited. Unfortunately, nonequivalent heavy dopants have finite solubility because of charge imbalance. Here, we propose a charge balance strategy for SnS by substituting Sn<sup>2+</sup> with Ag<sup>+</sup> and heavy Bi<sup>3+</sup>, improving the doping limit of Ag from 2% to 3%. Ag and Bi codoping increases the point defect concentration and introduces abundant boundaries simultaneously, scattering the phonons at both the atomic scale and nanoscale. The thermal conductivity of Ag<sub>0.03</sub>Bi<sub>0.03</sub>Sn<sub>0.94</sub>S decreased to 0.535 W·m<sup>−1</sup>·K<sup>−1</sup> at room temperature and 0.388 W·m<sup>−1</sup>·K<sup>−1</sup> at 275 ℃, which is below the amorphous limit of 0.450 W·m<sup>−1</sup>·K<sup>−1</sup> for SnS. This strategy offers a simple way to enhance the doping limit and achieve ultralow thermal conductivity in solids below the amorphous limit without precise structural modification.

Exploring the ultra-low lattice thermal conductivity of a two-dimensional compound Tl2Se3

Two-dimensional (2D) materials have attracted extensive attention in the field of thermoelectric (TE) materials, where heat transport properties play an important role in determining the performance of TE devices. In this paper, we investigate the thermal transport properties of novel 2D Tl2Se3 by means of first-principles approach combined with the Boltzmann transport equation (BTE). The small phonon sound group speed and strong anharmonicity are responsible for an ultra-low kl of 0.28 W/mK of 2D Tl2Se3 at room temperature. Meanwhile, the lattice thermal conductivity gradually decreases with the increase of temperature, indicating its potential value at high-temperature. The anti-bonding orbital filling between the Se-4p and Tl-6p states leads to the weak chemical bonds using the crystal orbital Hamiltonian population (COHP) analysis, which results in low phonon group velocities. Also, due to the strong acoustic-optical coupling in 2D Tl2Se3, the scattering processes of different acoustic modes is further studied to analyze how kl is suppressed. These findings demonstrate that 2D Tl2Se3 has potential applications in TE devices, which will motivate Tl2Se3 based experimental investigations.

Low lattice thermal conductivity of two-dimensional monolayers of BxN (x = 2, 3, and 5) induced by complex bonding networks: A comparative study with h-BN

It is well known that different bonding networks could bring a wide variety of physical properties to the materials although they hold analogous element and structure features. In this paper, we present a first-principles calculation about the lattice dynamics and phonon transport properties of two-dimensional (2D) boron-rich material BxN (x = 2, 3, and 5). The calculations show that besides the obvious differences in electrical properties compared to h-BN, the special bonding environment in these boron-rich materials also results in quite different phonon behaviors, where their thermal conductivity is at least one order of magnitude smaller than that of h-BN. By performing bonding and lattice dynamics analysis, we reveal that such dramatic reduction of conductivity is attributed to the synergistic effect of weak bond strength (low phonon group velocity) and complex bonding network (strong phonon scattering). Relative regular residual analysis further indicates that the four-phonon process is limited in BxN, and the three-phonon scattering is sufficient to describe their anharmonicity. Starting from the basic physical mechanism, the present study sheds light on the thermal transport properties of 2D boron-rich BxN compounds, which could provide useful insight for their widespread applications in thermal management.

First-principles study of wrinkled SnTe monolayer as p-type thermoelectric material

Tin telluride compounds are promising thermoelectric (TE) materials on account of the excellent electronic and thermal transport properties. The present work focuses on examining the TE performance of a two-dimensional wrinkled SnTe monolayer by employing the first-principles calculations and Boltzmann transport theory. The SnTe monolayer demonstrates high mechanical, dynamic and thermal stabilities, which have been thoroughly investigated using the elastic modulus, formation energy and ab initio molecular dynamics simulations. The lattice thermal conductivities of the SnTe monolayer along the zigzag- and armchair-direction are 11.29 and 12.40 W/mK at 300K, respectively. Due to the large Grüneisen parameters, short phonon relaxation time and low phonon group velocity, the p-type SnTe monolayer exhibits high TE performance at 900 K, as characterized by a high ZT of 1.44 along the zigzag-direction. Our present study not only offers valuable insights into the TE properties of the wrinkled SnTe monolayer, but also sheds some light on the theoretical designing of the novel SnTe-based material for TE applications.

In-doping induced resonant level and thermoelectric performance enhancement in n-type GeBi2Te4 single crystals with intrinsically low lattice thermal conductivity

Resonant level, the impurity level located inside the valence/conduction band, is an effective strategy for decoupling the electrical conductivity and Seebeck coefficient and enhancing the thermoelectric power factor. In this work, we show that In doping induces resonant level and enhances the thermoelectric performance of GeBi2Te4, a promising n-type thermoelectric material with layered structure. Single crystals grown by Bridgman method were used in this study to take the advantage of its anisotropic transport properties. An ultralow lattice thermal conductivity of ∼0.51 W m−1 K−1 at 323 K was found along the c-axis of GeBi2Te4, driven by intrinsic cation disorder and the low phonon group velocity from the relatively weak chemical bonds as well as the strong lattice anharmonicity caused by hierarchical bond orders. Both enhanced electrical conductivity and Seebeck coefficient were observed in the In-doped samples, indicating that In-doping not only increases the carrier concentration, but also introduces the resonant level that was further confirmed by the first-principles calculation. A maximum zT of ∼0.42 at 523 K and an average zT of 0.36 over 323 to 573 K were achieved in Ge0.97In0.03Bi2Te4 crystal sample, ∼100% and ∼89% enhancement compared to those of pristine single crystal sample, respectively. This study demonstrates another example of resonant level for thermoelectric performance enhancement, which may be applied to other related materials.

The influence of strong anharmonicity on high thermoelectric properties for the ternary compound NaMgX (X = As, Sb)

We theoretically analyzed the thermoelectric characteristics of the tetragonal NaMgX (X = As, Sb) compounds with strongly quartic anharmonicity based on an incorporation of first-principles calculations with self-consistent phonon theory and Boltzmann transport equations. These two materials show the low lattice thermal conductivity due to the low phonon group velocity. Since the flat band and the dispersion band coexist near the Fermi surface, the ZT values of p-type NaMgAs and NaMgSb at 900 K along the a(b) axis are 1.27 and 2.29, respectively. These results show that these two materials have good thermoelectric properties.

Ultra-low lattice thermal conductivity induces high-performance thermoelectricity in Janus group-VIA binary monolayers: A comparative investigation

In this paper, the electrical transport, thermal transport, and thermoelectric properties of two new Janus STe2 and SeTe2 monolayers are systematically studied by first-principles calculations, as well as the comparative with available literature’s results using different methods. It is found that the Seebeck coefficient and conductivity have opposite dependence on temperature, and we illustrate this phenomenon in detail. The decrease of the thermoelectric power factor (PF) with temperature originates from the decrease in conductivity. To obtain accurate and convergent lattice thermal conductivity, the root mean square (RMS) is calculated to obtain a reasonable cutoff radius for the calculation of third-order forces. Janus STe2 and SeTe2 monolayers exhibit ultra-low lattice thermal conductivity of 0.2 and 0.133 W/mK at 300 K, which result from the strong coupling effect between the acoustic mode and the low-frequency optical branch, low phonon group velocity, small phonon lifetime, and large anharmonicity. Consequently, ultra-high ZT values of 2.11 (2.09) and 3.28 (4.24) for n-type(p-type) carrier doping of STe2 and SeTe2 are obtained, indicating that they are promising thermoelectric materials.

High thermoelectric performance of TlInSe3 with ultra-low lattice thermal conductivity

Thermoelectric (TE) materials with an excellent thermoelectric figure of merit (ZT) provide an effective way to alleviate energy pressure and protect the environment. By applying the first-principles method, this paper makes a systematic study of the electronic and phonon transport properties of two-dimensional (2D) novel TlInSe3 utilizing the Boltzmann transport theory (BTE). The calculation results reveal that 2D TlInSe3 has an excellent power factor (0.81 × 10−2 W/mK2) and ultra-low lattice thermal conductivity (0.46 W/mK) at 300 K. We find that the low phonon group velocity and strong anharmonicity are the main factors leading to the ultra-low lattice thermal conductivity of TlInSe3. Meanwhile, by discussing the acoustic-optical scattering, we attribute low phonon group velocity and strong anharmonicity to the increase of scattering rates between acoustic mode and optical mode, which further suppresses the lattice thermal conductivity. In the analysis of electron and phonon transport properties, 2D TlInSe3, as a novel TE material, exhibits a ZT value as high as 4.15 at 500 K. Our research results show that TlInSe3 is a potential TE material, and the relevant analysis is significant in exploring new TE materials.

On-the-fly machine learning potential accelerated accurate prediction of lattice thermal conductivity of metastable silicon crystals

In this paper, we propose a convenient strategy to accelerate the evaluation of lattice thermal conductivity through combining phonon Boltzmann transport equation (PBTE) and on-the-fly machine learning potential (FMLP). The thermal conductivity of diamond silicon ($d\text{\ensuremath{-}}\mathrm{Si}$) is evaluated firstly by density functional theory (DFT), FMLP, and empirical potential with PBTE, respectively. The results demonstrate the proposed strategy integrates the prediction accuracy of DFT and computational speed of empirical potential, breaking the dilemma of traditional thermal conductivity assessment schemes. Based on this, the efficient strategy is applied to predict thermal conductivity of 102 low-energy metastable silicon crystals with energies between $d\text{\ensuremath{-}}\mathrm{Si}$ and experimentally ${\mathrm{Si}}_{24}$. Among them, the $Cmcm\text{\ensuremath{-}}{\mathrm{Si}}_{16}, P6/mmm\text{\ensuremath{-}}{\mathrm{Si}}_{36}$-2, $Pnma\text{\ensuremath{-}}{\mathrm{Si}}_{32}$-2 are predicted to host lowest lattice thermal conductivity in $xx$ (8.213 ${\mathrm{Wm}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$), $yy$ (10.917 ${\mathrm{Wm}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$), and $zz$ (11.807 ${\mathrm{Wm}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$) directions, respectively. Such low lattice thermal conductivity benefits from the combined effect of low phonon group velocity and intense phonon scattering caused by distorted $s{p}^{3}$ hybrid states in these metastable silicon crystals. The findings presented in this work provide new candidates and insights of silicon-based materials with ultra-low thermal conductivity, which will greatly expand the applications in thermoelectric and thermal insulation fields.

The stability, mechanical, electronic and thermoelectric properties of unexplored monolayer Ca4Sb2O and Ca4Bi2O

Thermoelectric materials can directly convert heat gradient into electricity, thus have attracted much attention in the field of clean energy and ecological protection. In this work, we proposed two novel two−dimensional materials, Ca4Sb2O and Ca4Bi2O, and investigated their stability, mechanical, electronic and thermoelectric properties. We revealed that these two monolayers are direct semiconductors with bandgaps of 1.57 and 1.08 eV, respectively. Due to the lower electron effective mass, the electron mobilities (252.90–799.97 cm2/Vs) are significantly higher than those of hole (58.16–59.21 cm2/Vs), leading to high n-type conductivities (106–107 S/m), as well as high thermoelectric power factors of 28.80 and 10.83 mW K−2 m−1 at 300 K. Also, owing to the low phonon group velocities and high phonon-phonon scattering rates, the monolayers also possess low lattice thermal conductivities of 1.86 and 1.01 W/mK at room temperature, which are dominated by acoustic modes. As a result, Ca4Sb2O and Ca4Bi2O deliver high n-type thermoelectric figure of merit of 0.27 and 0.29 at 300 K, and increase even further to 1.50 and 1.67 at 700 K, suggesting that they are candidates for low - medium temperature thermoelectric appliances.

A thermal conductivity switch via the reversible 2H-1T′ phase transition in monolayer MoTe2

The two-dimensional (2D) material-based thermal switch is attracting attention due to its novel applications, such as energy conversion and thermal management, in nanoscale devices. In this paper, we observed that the reversible 2H–1T′ phase transition in MoTe2 is associated with about a fourfold/tenfold change in thermal conductivity along the X/Y direction by using first-principles calculations. This phenomenon can be profoundly understood by comparing the Mo–Te bonding strength between the two phases. The 2H-MoTe2 has one stronger bonding type, while 1T′-MoTe2 has three weaker types of bonds, suggesting bonding inhomogeneity in 1T′-MoTe2. Meanwhile, the bonding inhomogeneity can induce more scattering of vibration modes. The weaker bonding indicates a softer structure, resulting in lower phonon group velocity, a shorter phonon relaxation lifetime and larger Grüneisen constants. The impact caused by the 2H to 1T′ phase transition in MoTe2 hinders the propagation of phonons, thereby reducing thermal conductivity. Our study describes the possibility for the provision of the MoTe2-based controllable and reversible thermal switch device.

NaBeAs and NaBeSb: Novel Ternary Pnictides with Enhanced Thermoelectric Performance

Thermoelectrics is a clean energy technology that converts thermal energy into electrical energy and provides an environmentally friendly and viable route to produce electricity. In this work, we thoroughly explore the thermoelectric performance of two novel ternary pnictide compounds, NaBeAs and NaBeSb, using full ab initio calculations and solving linear Boltzmann transport equations. We predict that both compounds exhibit excellent dynamical and thermal stability. The combined effect of low phonon group velocity and weak bonding interaction results in intrinsic low lattice thermal conductivities of 1.41 and 0.59 W/mK for NaBeAs and NaBeSb, respectively, in the z-axis direction at 600 K. The electronic structure exhibits high conduction band degeneracy, which results in favorable electrical transport characteristics. The unique combination of very low lattice thermal conductivity and good electrical transport properties leads to excellent n-type thermoelectric properties. Furthermore, in n-type doping, the figures of merit reach 1.82 and 4.26 for NaBeAs and NaBeSb at 600 K. Our findings show that both compounds are promising n-type thermoelectric materials at medium temperatures.

Thermoelectric transport properties of orthorhombic RbBaX (X = Sb, Bi) with strong anharmonicity.

The thermoelectric properties of RbBaX (X = Sb, Bi), an anisotropic material with strong anharmonicity, are systematically studied by first-principles calculations, combined with the self-consistent phonon theory and the Boltzmann transport equation. A reasonable lattice thermal conductivity κL is captured by fully handling the phonon frequency shift and four-phonon scattering caused by the quartic anharmonicity. The κL of RbBaSb and RbBaBi along the a-axis is only 0.60 and 0.36W m-1 K-1 at 300K, respectively, which is much lower than that of most thermoelectric materials. The low phonon group velocity resulting from the unusually weak atomic bonding strengths along the a-axis is the origin of the ultralow κL. Furthermore, the high dispersion near the conduction band minimum enables n-type doping with a higher electrical conductivity. The results show that orthorhombic RbbaBi has a ZT as high as 1.04 at 700K along the a-axis direction, indicating its great application potential in the thermoelectric field.

Janus 2H-MXTe (M = Zr, Hf; X = S, Se) monolayers with outstanding thermoelectric properties and low lattice thermal conductivities.

Two-dimensional (2D) materials have been one of the most popular objects in the research field of thermoelectric (TE) materials and have attracted substantial attention in recent years. Inspired by the synthesized 2H-MoSSe and numerous theoretical studies, we systematically investigated the electronic, thermal, and TE properties of Janus 2H-MXTe (M = Zr and Hf; X = S and Se) monolayers by using first-principles calculations. The phonon dispersion curves and AIMD simulations confirm the thermodynamic stabilities. Moreover, Janus 2H-MXTe were evaluated as indirect band-gap semiconductors with band gaps ranging from 0.56 to 0.90 eV using the HSE06 + SOC method. To evaluate the TE performance, firstly, we calculated the temperature-dependent carrier relaxation time with acoustic phonon scattering τac, impurity scattering τimp, and polarized scattering τpol. Secondly, the calculation of lattice thermal conductivity (κl) shows that these monolayers possess relatively poor κl with values of 3.4-5.4 W mK-1 at 300 K, which is caused by the low phonon lifetime and group velocity. After computing the electronic transport properties, we found that the n-type doped Janus 2H-MXTe monolayers exhibit a high Seebeck coefficient exceeding 200 μV K-1 at 300 K, resulting in a high TE power factor. Eventually, combining the electrical and thermal conductivities, the optimal dimensionless figure of merit (zT) at 300 K (900 K) can be obtained, which is 0.94 (3.63), 0.51 (2.57), 0.64 (2.72), and 0.50 (1.98) for n-type doping of ZrSeTe, HfSeTe, ZeSTe, and HfSTe monolayers. Particularly, the ZrSeTe monolayer shows the best TE performance with the maximal zT value. These results indicate the excellent application potential of Janus 2H-MXTe (M = Zr and Hf; X = S and Se) monolayers in TE materials.

Atomic site-targeted doping in Ti2FeNiSb2 double half-Heusler alloys: zT improvement via selective band engineering and point defect scattering

Ti2FeNiSb2 is a promising double half-Heusler thermoelectric compound with intrinsically low thermal conductivity due to low phonon group velocity. Since it is introduced in 2019, many efforts have been focused on further reducing its thermal conductivity via doping. However, the effects of doping on its electronic transport properties have been neglected. Here, we investigate the effects of doping Co and Bi at the Fe- and Sb-sites, respectively, in Ti2FeNiSb2 for the first time. Changes in band parameters due to atomic site-targeted doping are estimated by the Single Parabolic Band model. Bypassing the trade-off relation between the Seebeck coefficient and electrical conductivity is observed when doping Co at Fe-sites. The physics behind the bypass is explained in terms of temperature-dependent reduced chemical potential and non-degenerate mobility. As a result, peak figure of merit zT values of ∼0.69 in Ti2Fe0.9Co0.1NiSb2 is achieved, which is approximately six times higher than that of the pristine Ti2FeNiSb2. The thermoelectric performance of Ti2FeNiSb2 can be improved by selective band engineering to bypass the Seebeck coefficient-electrical conductivity trade-off relation from atomic-site targeted doping.