High Temperature Thermoelectric Materials Research Articles

Two-dimensional Li-based ternary chalcogenides LiMTe2 (M = Al, Ga, and In): Promising high-temperature thermoelectric materials

High-efficiency thermoelectric materials require two essential characteristics; low lattice thermal conductivity (κl) and high power factor (PF). Although group-III chalcogenides exhibit extremely high PF, their high κl hinders their practical applications. Through first-principles calculations, we have discovered that the LiMTe2 (M = Al, Ga, and In) monolayers, which have a similar structure stacking as the group-III chalcogenides, simultaneously possess the two key characteristics mentioned above. The κl values of the LiMTe2 monolayers are as low as 1.4−2.0 W m−1 K−1 at room temperature. Detailed analysis of bonding characteristics and phonon scattering rates suggests that the ultralow κl can be mainly attributed to the strong bond anharmonicity, which is a result of the cooperative endeavor of bond heterogeneity (coexistence of strong covalent bonds and weak ionic bonds) and the existence of lone-pair electrons. Additionally, the “pudding-mold” type of the conduction band near the Fermi level contributes to the high power factor of LiMTe2 monolayers. Therefore, the ZT values of n-type doped LiMTe2 monolayers exceed 1 at T = 800 K and carrier conentration of 1.71 × 1012–3.32 × 1012 cm−2, indicating the great potential of the 2D LiMTe2-family under n-type doping as high-temperature thermoelectric materials. The current work suggests that increasing bond complexity and the introduction of lone-pair electrons are strategic pathways for designing high-performance thermoelectric materials.

Effects of Magnetic Fe Doping on the Thermoelectric Properties of TiNiSn Nanomaterials prepared via melt spinning method

As a kind of high temperature thermoelectric material, TiNiSn compound has the characteristics of high power factor and high thermal conductivity. Its thermoelectric performance is largely limited by the high thermal conductivity. In this paper, TiNiFexSn(x=0-0.05) samples are prepared by melt spinning combined with spark plasma sintering method. The results show that there are nanocrystals existed in the samples with a size of around 200nm. The grain size of the samples is refined through the melt-spinning process, and the lattice thermal conductivity is lower compared with the arc-melted samples. With the increase of Fe content, the lattice thermal conductivity of TiNiFexSn samples decreases, reaching a minimum value of 3.31W/mK when x=0.02, which is 44% lower than that of TiNiSn matrix. The carrier concentration of TiNiFexSn samples increases due to the doping of Fe, resulting in an increase of electrical conductivity and decrease of Seebeck coefficient and finally improvement of the power factor. The maximum zT value of TiNiFe0.03Sn sample is 0.54 at 900K, which is 35% higher than that of TiNiSn samples. This work shows that the melt spinning and magnetic Fe doping can effectively improve the thermoelectric properties of TiNiSn.

Thermoelectric properties of half-Heusler alloys

Half-Heusler alloys (HHs) as medium- and high-temperature thermoelectric materials have attracted increasing considerable attention, owing to their excellent mechanical properties and thermal stability. Nonetheless, the intercoupling between the Seebeck coefficient and electrical conductivity, and their high thermal conductivity limit the furthermore enhancement of their thermoelectric properties. This review systemically summarizes and analyses the various current strategies for improving thermoelectric properties, such as manipulating band structure, optimizing electron and phonon transports, and constructing high configurational entropy, etc. Moreover, the possible deficiencies of the existing electric-phonon transport mechanisms are highlighted and discussed, which aiming to provide a meaningful guide for future efforts to accelerate the development of HHs. Finally, based on current research, a new potential future for the integration of single crystal technology and high-entropy effect is introduced for HHs.

Thermoelectric properties of heavily Co-doped β-FeSi2

Element doping is a widely employed strategy to enhance the thermoelectric (TE) properties of various materials. β-FeSi2 is a promising low-cost high-temperature TE material with exceptional thermal stability; however, the doping limit of β-FeSi2 is usually very low, which limits the tunability of electrical and thermal properties. Recently, a high doping content of 0.16 in β-FeSi2 has been achieved by the introduction of iridium (Ir), leading to the highest reported figure of merit (zT) of 0.6 in β-FeSi2. Motivated by the successful heavy doping with Ir, this work aims to explore element heavy doping in β-FeSi2 with cobalt (Co), a cheaper, more readily available dopant with a smaller atomic radius and closer electronegativity to iron (Fe). In this study, we successfully obtained a record-high doping content of 0.24 in Co-doped β-FeSi2 through a prolonged annealing process. Despite the absence of a substantial enhancement in the zT of Co-doped β-FeSi2 at high doping levels, with a maximum zT of 0.3 at 900 K in Fe0.92Co0.08Si2, we observed a transition in the carrier transport mechanism as a function of Co doping content, attributed to changes in the band structure. At a low Co doping content (x ≤ 0.12), Fe1–xCoxSi2 demonstrates dominant carrier transport via impurity levels within the band gap, exhibiting hopping conduction. As the Co doping content increases (x > 0.16), the impurity levels overlap and form an impurity band, and the carrier transport turns into the impurity band conduction. The observed band conduction behavior of Fe1–xCoxSi2 (x > 0.16) mirrors that of Ir-doped β-FeSi2, but Fe1–xCoxSi2 shows much lower mobility, which can be attributed to the localized feature of the impurity band introduced by the Co doping. Overall, this study provides insights into the heavy Co doping and its influence on the TE properties and carrier conduction mechanisms in β-FeSi2, helpful for the further development of this TE system.

Decomposed defect formation energy for analysis of doping process: The case of n-type and p-type doping of β-FeSi2

Defect formation energy governs the thermodynamics of a specific dopant within the host material. Here, we introduce an approach to decomposing the defect formation energy into intuitive components, each representing a distinct physical step in the process of defect formation. Through this approach, we illustrate that adhering solely to conventional criteria, such as ionic radius, may overlook potential dopants. Taking β-FeSi2, a promising high-temperature thermoelectric material, as an example, we demonstrate that non-intuitive chemical interactions can play a more significant role in lowering the defect formation energy. As a result, Ir on Fe site is found to exhibit unexpected low defect formation energy among the 26 candidate dopants and has been employed in experiment to enhance the thermoelectric figure of merit of n-type β-FeSi2. The understanding gained from this work could be of general interest for addressing the doping limit issue for other potential thermoelectric materials.

Dopant dependent microstructure of hot-pressed SiGe alloys and its implications on thermoelectric properties

SiGe is a proven high temperature thermoelectric material for space application. We have investigated the role of dopants (P and B) on the densification of SiGe alloys. It was observed that on P doping there is a formation of liquidous SiP phase in the SiGe matrix during hot pressing that improves the diffusion across grain boundaries and as a result ∼98 % of theoretical density was achieved. In case of identically prepared B doped samples, the segregation of B resulted in porous microstructure and low density ∼89 %. Such a difference in microstructure resulted a figure-of-merit of ∼1.29 (at 1100K) for n-type SiGe (P doped) and ∼0.86 (at 1100K) for p-type SiGe (B doped) at a hot press temperature of 1273 K. The study suggests that in case of SiGe apart from doping the densification of materials plays a very important role in improving its thermoelectric performance.

Tweaking the interplay of the layers by substitution in Ca3Co4O9+δ for high efficiency thermoelectric materials

Ca3Co4O9 is a well-known high temperature thermoelectric material owing to its sandwich type layered structure consisting of both conducting and insulating slabs. In the present study we attempt to enhance the electrical conductivity without affecting the thermal conductivity by suitable doping in these layers. Compositions with a general formula Ca3−xSrxCo4−xMgx/2Tix/2O9+δ (0 ≤ x ≤ 0.15) were prepared by conventional solid state method and subjected to routine characterization techniques like XRD, SEM and XPS. Sr substitution in the insulating layer and Mg, Ti substitution in the conductive layer led to a decrease in the electrical resistivity from 17.86 mΩ cm to 9.74 mΩ cm, which resulted in an increase in the power factors. The dimensionless thermoelectric figure of merit ZT is found to be 0.13 at 873 K for x = 0.15, which is ̴2.1 times higher than the parent compound attributed to the excess oxygen in the doped composition.

Impact of Lu-Substitution in Yb14-xLuxZnSb11: Thermoelectric Properties and Oxidation Studies.

Yb14ZnSb11 is one of the newest additions to the high-performance Yb14MSb11 (M = Mn, Mg, and Zn) family of p-type high-temperature thermoelectric materials and shows promise for forming passivating oxide coatings. Work on the oxidation of rare earth (RE)-substituted Yb14-xRExMnSb11 single crystals suggested that substituting late RE elements may form more stable passivation oxide coatings. Yb14-xLuxZnSb11 (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7) samples were synthesized, and Lu-substitution's effects on thermoelectric and oxidation properties are investigated. The solubility of Lu within the system was found to be quite low with xmax ∼ 0.3; samples with x > 0.3 contained impurities of LuSb. Goldsmid-Sharp band gap estimations show that introducing Lu reduces the apparent band gap. Because of this, the Lu-substituted samples show a reduction in the maximum Seebeck coefficient, decreasing the high-temperature zT. This contrasts with the impact of Lu3+ substitution in Yb14MnSb11, where the addition of Lu3+ for Yb2+ results in increases in both resistivity and the Seebeck coefficient. Oxidation of the x = 0.3 solid solution was studied by thermogravimetric- differential scanning calorimetry , powder X-ray diffraction, scanning electron microscopy-energy-dispersive spectroscopy, and optical images. The samples show no mass gain before 785 K, and ensuing oxidation reactions are proposed. At the highest temperatures, significant amounts of Yb14-xLuxZnSb11 remained beneath an oxide coating, suggesting that passivation may be achievable in oxygen environments.

The filled tetrahedral compound NaZnP with strong quartic anharmonicity and good thermoelectric properties

Based on first-principles calculations, self-consistent phonon (SCP) theory, and the Boltzmann transport equation, we investigate the thermal transport and thermoelectric properties of the Nowotny-Juza filled tetrahedral compound NaZnP. The effects of anharmonic phonon renormalization and four-phonon scattering on the heat transport of NaZnP are also considered. The weak binding and rattling-like vibrational behavior of Na atoms lead to strong lattice anharmonicity, and the results show that NaZnP has low lattice thermal conductivity. Furthermore, the coexistence of high dispersion and high degeneracy of valence band maxima leads to high power factor under p-type doping. The combination of low lattice thermal conductivity and good electrical transport properties results in high thermoelectric performance. This indicates that NaZnP is a promising p-type high-temperature thermoelectric material.

Enhancement of thermoelectric performance in n-type Si90Ge10-based alloy by metallic Zn doping

Silicon–germanium (SiGe) alloy has become one of the representative high-temperature thermoelectric (TE) materials due to its advantages of stability, non-toxicity, oxidation resistance, and high mechanical strength. However, the high thermal conductivity and expensive Ge greatly limit the enhancement of zT value and its application. In this paper, n-type Si90Ge10P2Znx nanocomposites were prepared by ball milling and spark plasma sintering. By adjusting the Zn content and sintering time, multiple phonon-scattering centers, such as Zn precipitates, nano-pores, and layered structures, have been introduced into the SiGe matrix. The thermal conductivity was significantly reduced to 2.59 W m−1 K−1 without deteriorate power factor (PF), thus leading to a high zT value of 1.23 at 873 K. At 323–873 K, the average zT value (zTavg) also reached 0.6, increased by approximately 25% in comparison to the reported value using the same ratio of Si90Ge10. Compared with the conventional radioisotope TE generator with Si80Ge20 composition, the zTavg value increased by nearly 30% with only half of Ge, giving strong impetus to the application of SiGe-based TE materials.

First-principles studies on the structural, electronic and thermal transport characteristics of half-Heusler compounds LiXN (X=Mg, Zn)

The electronic structures and thermal transport properties of the half-Heusler (HH) compounds LiMgN and LiZnN are calculated in detail by combining first-principles calculations with Boltzmann transport theory. Our phonon calculations showed that LiMgN and LiZnN are dynamic stability. The calculated bulk moduli and equilibrium lattice constants are in good agreement with the experimental and available theoretical data. The electronic band structures obtained by PBE (HSE06) method indicate that both LiMgN and LiZnN are direct bandgap semiconductors with band gaps of 2.33 eV (3.23 eV) and 0.53 eV (1.42 eV), respectively. It is shown that the Li–N，Li–Mg and Li–Zn are ionic bond via ELF analysis. At room temperature, the calculated lattice thermal conductivities of LiMgN and LiZnN compounds are 19.31 Wm−1K−1 and 18.74 Wm−1K−1, respectively; But with the external temperature increases to 1100 K, their lattice thermal conductivities are decrease rapidly to 4.96 Wm−1K−1 and 4.32 Wm−1K−1, respectively. Moreover, we analyzed the mean free paths, phase volume spaces (P3), Gruneisen parameters (γ), scattering rates and group velocities in detail in order to further understand the origins of their relatively low lattice thermal conductivities and corresponding microscopic mechanism. We also investigated thermoelectric performances of LiMgN and LiZnN under different temperatures, and our results showed that with the external temperature increasing from 300 K to 1100 K, the maximum ZT values can increase from 0.05 (0.03) and 1.83 (1.32) for LiMgN (LiZnN), indicating that they are potential high-temperature thermoelectric materials. Our work can offer some theoretical references for improving thermoelectric performance and for future experimental studies.

Evolution of Thermoelectric and Oxidation Properties in Lu-Substituted Yb14MnSb11

Yb14MnSb11 is one of the state-of-the-art high-temperature p-type thermoelectric materials with reported zTs of 1.2–1.3 at 1273 K. Site substitution of Yb14MnSb11 provides a means to control carrier concentration and impacts the oxidation kinetics. Substitution of Lu3+ for Yb2+ in Yb14MnSb11 single crystals has been shown to provide faster oxidation kinetics compared with the pristine phase, and it has been speculated that this may lead to surface passivation. Polycrystalline samples of Yb14–xLuxMnSb11 were synthesized from the elements and through a route utilizing YbH2, MnSb, and Yb4Sb3 as reactive precursors. The solubility of Lu was found to be less than x = 0.5, and at that composition and above LuSb impurities are observed in the powder X-ray diffraction. Because Lu3+ is substituting for Yb2+ in a p-type system, there is an increase in both the electrical resistivity and Seebeck coefficient with Lu substitution. As Yb14MnSb11 has been predicted to be optimally doped ∼1.5 × 1021 h+ cm–3, this reduction in carrier concentration in the solid solution of Yb14–xLuxMnSb11 decreases the peak zT. Oxidation of Yb13.7Lu0.3MnSb11 as a function of temperature was studied. At low temperatures, the Lu-substituted sample may have improved oxidation resistance through forming a passivating oxide film on the surface.

Enhancing thermoelectric properties of MCoSb-based alloys by entropy-driven energy-filtering effects and band engineering

MCoSb-based medium-entropy half-Heusler (HH) alloy with low lattice thermal conductivity (κL) is a promising medium- and high-temperature thermoelectric material. However, the unexpected band structure of the alloy leads to a sudden decrease in the Seebeck coefficient (S), which severely restricts the optimization of the figure-of-merit (ZT). In this study, we demonstrate a new concept for decoupling S and electrical conductivity (σ) based on entropy engineering. This method involves band engineering and the energy-filtering effect, where the entropy-driven quantum confinement effect is manipulated to filter low-energy electrons, and the increasing entropy promotes a rapidly changing density of state near Fermi level. Consequently, an excellent S of ∼ −211.6 μV K−1 at 923 K was achieved for the M0.82Nb0.18CoSb HH alloy, which is 62.3% higher than that of the pristine M0.85N0.15CoSb (M = Ti, Zr, Hf; N= V, Ta; equimolar) HH alloy (∼−130.4 μV K−1). Moreover, benefiting from the optimization of S and κL, a peak ZT was enhanced from ∼0.17 for the pristine M0.85N0.15CoSb medium-entropy HH alloy to 0.58 for the M0.85Nb0.15CoSb high-entropy HH alloy. These results broaden the applications of entropy-engineering to decrease κL and decoupling between S and σ.

In-situ growth of carbon nanotubes on ZnO to enhance thermoelectric and mechanical properties

As a high-temperature thermoelectric (TE) material, ZnO offers advantages of non-toxicity, chemical stability, and oxidation resistance, and shows considerable promise as a true ready-to-use module under air conditions. However, poor electrical conductivity and high thermal conductivity severely hinder its application. Carbon nanotubes (CNTs) are often used as a reinforcing phase in composites, but it is difficult to achieve uniform dispersion of CNTs due to van der Waals forces. Herein, we developed an effective in-situ growth strategy of homogeneous CNTs on ZnO nanoparticles by exploiting the chemical vapor deposition (CVD) technology, in order to improve their electrical conductivity and mechanical properties, as well as reducing the thermal conductivity. Meanwhile, magnetic nickel (Ni) nanoparticles are introduced as catalysts for promoting the formation of CNTs, which can also enhance the electrical and thermal transportation of ZnO matrices. Notably, the electrical conductivity of ZnO is significantly boosted from 26 to 79 S·cm−1 due to the formation of dense and uniform conductive CNT networks. The lattice thermal conductivity (κL) is obviously declined by the intensification of phonon scattering, resulting from the abundant grain boundaries and interfaces in ZnO-CNT composites. Importantly, the maximum dimensionless figure of merit (zT) of 0.04 at 800 K is obtained in 2.0% Ni-CNTs/ZnO, which is three times larger than that of CNTs/ZnO prepared by traditional ultrasonic method. In addition, the mechanical properties of composites including Vickers hardness (HV) and fracture toughness (KIC) are also reinforced. This work provides a valuable reference for dispersing nano-phases in TE materials to enhance both TE and mechanical properties.

Comprehensive investigation of the extremely low lattice thermal conductivity and thermoelectric properties of BaIn2Te4

Recently, an extremely low lattice thermal conductivity value has been reported for the alkali-based telluride material ${\mathrm{BaIn}}_{2}{\mathrm{Te}}_{4}$. The value is comparable with low-thermal conductivity metal chalcogenides, and the glass limit is highly intriguing. Therefore, to shed light on this issue, we performed first-principles phonon thermal transport calculations. We predicted highly anisotropic lattice thermal conductivity along different directions via the solution of the linearized phonon Boltzmann transport equation. More importantly, we determined several different factors as the main sources of the predicted ultralow lattice thermal conductivity of this crystal, such as the strong interactions between low-frequency optical phonons and acoustic phonons, small phonon group velocities, and lattice anharmonicity indicated by large negative mode Gr\"uneisen parameters. Along with thermal transport calculations, we also investigated the electronic transport properties by accurately calculating the scattering mechanisms, namely the acoustic deformation potential, ionized impurity, and polar optical scatterings. The inclusion of spin-orbit coupling (SOC) for electronic structure is found to strongly affect the $p$-type Seebeck coefficients. Finally, we calculated the thermoelectric properties accurately, and the optimal $ZT$ value of $p$-type doping, which originated from high Seebeck coefficients, was predicted to exceed unity after 700 K and have a direction averaged value of 1.63 (1.76 in the $y$-direction) at 1000 K around $2\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ hole concentration. For $n$-type doping, a $ZT$ around $3.2\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ concentration was predicted to be a direction-averaged value of 1.40 (1.76 in the $z$-direction) at 1000 K, mostly originating from its high electron mobility. With the experimental evidence of high thermal stability, we showed that the ${\mathrm{BaIn}}_{2}{\mathrm{Te}}_{4}$ compound has the potential to be a promising mid- to high-temperature thermoelectric material for both $p$-type and $n$-type systems with appropriate doping.

D-Orbital-Driven Low Lattice Thermal Conductivity in TiRhBi: A Root for Potential Thermoelectric and Microelectronic Performance

Half-Heusler (HH) compounds are high-temperature thermoelectric materials with a high power factor upon appropriate doping. However, the efficiency and ZT values are still low due to their high lattice thermal conductivity, κl. It is essential to understand the thermal transport properties to design a potential thermoelectric material such as HH and a microelectronic device in general. At high temperatures, the κl is dominated by intrinsic scattering rates which arise purely from the anharmonic potential of the system. We study theoretically HH compounds, TiRhBi and TiCoBi, with the density functional theory and Boltzmann transport theory for κl calculation. We find that TiRhBi has a much lower κl (2.6 W/mK) than TiCoBi (6.4 W/mK) at 1000 K due to the weaker bond formation capability of diffused Rh 4d-electrons compared to the corresponding narrow band of 3d-electrons of Co in TiCoBi. The diffused Rh 4d-electrons near the valence band maximum participate in the nonbonding and antibonding types of overlap. This leads to an extremely weaker bond strength of TiRhBi, as evident from the COHP analysis. The weaker bond strength corresponds to an anharmonic potential which results in anharmonic effects leading to a lower κl. We discuss in detail several intermediate quantities such as COOP/COHP, heat capacity, phonon entropy, group velocity, Grüneisen parameter, and anharmonic scattering rates to explain the κl magnitudes.

High thermoelectric properties of P-SiGe/Sr0.9La0.1Ti0.9−xZrxNb0.1O3 composite

SrTiO3 is a high temperature thermoelectric material with calcium titanite structure that is environmentally friendly and affordable, but the high thermal conductivity at high temperatures limits its development, so how to maintain high electrical properties while reducing thermal conductivity is the most important problem facing SrTiO3. SiGe and SrTiO3 are both thermoelectric materials in the intermediate and high temperature region and have a lot of commonalities, and it is likely to obtain high thermoelectric properties through the interfacial effect of both, however, there is not any study on the compound regulation of the two. Therefore, in this study, phosphorus (P)-doped SiGe was compounded with Zr, La and Nb co-doped SrTiO3. 3 mol.%SiGe(C)/97 mol.% Sr[Formula: see text]La[Formula: see text]Ti[Formula: see text]Zr[Formula: see text]Nb[Formula: see text]O3(Zr1Si3(C)) obtained by sintering under carbon reducing atmosphere shows a relatively large power factor of and low thermal conductivity of 2.88 Wm[Formula: see text]K[Formula: see text] at 1000 K, achieve a ZT value to 0.42 at 1000 K. This is at a high level in this study of SrTiO3 composite thermoelectric materials and provides a new idea for the subsequent study of composite modulation.

Y2Te3: A New n-Type Thermoelectric Material.

Rare-earth chalcogenides Re3-xCh4 (Re = La, Pr, Nd, Ch = S, Se, and Te) have been extensively studied as high-temperature thermoelectric (TE) materials owing to their low lattice thermal conductivity (κL) and tunable electron carrier concentration via cation vacancies. In this work, we introduce Y2Te3, a rare-earth chalcogenide with a rocksalt-like vacancy-ordered structure, as a promising n-type TE material. We computationally evaluate the transport properties, optimized TE performance, and doping characteristics of Y2Te3. Combined with a low κL, multiple low-lying conduction band valleys yield a high n-type TE quality factor. We find that a maximum figure of merit zT > 1 can be achieved when Y2Te3 is optimally doped to an electron concentration of 1-2 × 1020 cm-3. We use defect calculations to show that Y2Te3 is n-type dopable under Y-rich growth conditions, which suppress the formation of acceptor-like cation vacancies. Furthermore, we propose that optimal n-type doping can be achieved with halogens (Cl, Br, and I), with I being the most effective dopant. Our computational results as well as experimental results reported elsewhere motivate further optimization of Y2Te3 as an n-type TE material.

Unlocking the thermoelectric potential of the Ca14AlSb11 structure type.

Yb14MnSb11 and Yb14MgSb11 are among the best p-type high-temperature (>1200 K) thermoelectric materials, yet other compounds of this Ca14AlSb11 structure type have not matched their stability and efficiency. First-principles computations show that the features in the electronic structures that have been identified to lead to high thermoelectric performances are present in Yb14ZnSb11, which has been presumed to be a poor thermoelectric material. We show that the previously reported low power factor of Yb14ZnSb11 is not intrinsic and is due to the presence of a Yb9Zn4+xSb9 impurity uniquely present in the Zn system. Phase-pure Yb14ZnSb11 synthesized through a route avoiding the impurity formation reveals its exceptional high-temperature thermoelectric properties, reaching a peak zT of 1.2 at 1175 K. Beyond Yb14ZnSb11, the favorable band structure features for thermoelectric performance are universal among the Ca14AlSb11 structure type, opening the possibility for high-performance thermoelectric materials.

Enhanced High-Temperature Thermoelectric Performance by Strain Engineering in BiOCl

Semiconductor BiOCl has a layered structure with ultralow lattice thermal conductivity [Q.D. Gibson et al., Science 373, 1017--1022 (2021)] and has potential applications in the field of thermoelectric materials. In the present study, the thermoelectric properties of BiOCl crystals are accurately predicted using the first-principles calculation combined with Boltzmann transport theory. The dimensionless figure of merit ($ZT$) of $p$-type BiOCl is found to be 0.2 at room temperature, reaching 1.1 at 800 K. In addition, applying in-plane biaxial tensile strain ${ϵ}_{xy}$ can lead to a further increase in the value of $ZT$ to 1.9 at 800 K. This means that $p$ BiOCl is an excellent high-temperature thermoelectric material. And this is due to the fact that biaxial strain drastically reduces the lattice thermal conductivity and the shift of the valence band toward the Fermi level can optimize the carrier concentration. Thus, the present work paves a way for the design of adjustable high-temperature thermoelectric materials.