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Sb2Te3 alloys are promising thermoelectric materials because of their outstanding electrical transport properties in the midtemperature range of 500–700 K, while codoping with multiple elements has been successful to improve their thermoelectric performance. In this study, enhanced thermoelectric properties with a maximum thermoelectric figure of merit of 0.97 are reported for singly and lightly Pb-doped Sb2Te3 polycrystalline alloys (Sb2– x Pb x Te3). Very light Pb doping in the range 0.005 ≤ x ≤ 0.0125 in the Sb2– x Pb x Te3 alloys yielded significantly improved carrier transport properties and increased electrical conductivity while the Seebeck coefficient is decreased moderately, since the density-of-state effective mass is improved much. As a result, power factor for the Pb-doped Sb2Te3 is largely increased up to 3.7 mW/mK2 at 300 K. The lattice thermal conductivity decreased considerably owing to the additional point defect phonon scattering by the Pb despite slight doping. Consequently, a maximum thermoelectric figure of merit of 0.97 was obtained for Sb1.9875Pb0.0125Te3 (x = 0.0125) at 600 K, which is the highest reported value for singly doped Sb2Te3-based alloys. A maximum energy conversion efficiency was calculated to be 9.0% for a temperature difference of 350 K, which is higher than that for other singly or codoped Sb2Te3 alloys. [ABSTRACT FROM AUTHOR]

Some transition-metal dichalcogenides have been actively studied recently owing to their potential for use as thermoelectric materials due to their superior electronic transport properties. Iron-based chalcogenides, FeTe2, FeSe2 and FeS2, are narrow bandgap (~1 eV) semiconductors that could be considered as cost-effective thermoelectric materials. Herein, the thermoelectric and electrical transport properties FeSe2–FeS2 system are investigated. A series of polycrystalline samples of the nominal composition of FeSe2−xSx (x = 0, 0.2, 0.4, 0.6, and 0.8) samples are synthesized by a conventional solid-state reaction. A single orthorhombic phase of FeSe2 is successfully synthesized for x = 0, 0.2, and 0.4, while secondary phases (Fe7S8 or FeS2) are identified as well for x = 0.6 and 0.8. The lattice parameters gradually decrease gradually with S content increase to x = 0.6, suggesting that S atoms are successfully substituted at the Se sites in the FeSe2 orthorhombic crystal structure. The electrical conductivity increases gradually with the S content, whereas the positive Seebeck coefficient decreases gradually with the S content at 300 K. The maximum power factor of 0.55 mW/mK2 at 600 K was seen for x = 0.2, which is a 10% increase compared to the pristine FeSe2 sample. Interestingly, the total thermal conductivity at 300 K of 7.96 W/mK (x = 0) decreases gradually and significantly to 2.58 W/mK for x = 0.6 owing to the point-defect phonon scattering by the partial substitution of S atoms at the Se site. As a result, a maximum thermoelectric figure of merit of 0.079 is obtained for the FeSe1.8S0.2 (x = 0.2) sample at 600 K, which is 18% higher than that of the pristine FeSe2 sample. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides have being actively studied on the account of their large density‐of‐state effective mass and low lattice thermal conductivity. Herein, thermoelectric and electrical transport properties of MoSe2–MoTe2 system are investigated. A series of Mo(Se1−xTex)2 (x = 0,.25,.5,.75, and 1) polycrystalline samples was synthesized by conventional solid‐state reaction. Single hexagonal phase was identified for each sample without secondary phase, confirming the formation of complete solid solutions between MoSe2 and MoTe2. The electrical conductivity and magnitude of the Seebeck coefficient increased simultaneously with increasing Te content x at high temperatures, with the power factor following the same trend. As results, the MoTe2 sample exhibited the maximum power factor of.014 mW/(m K2) at 823 K. The lattice thermal conductivities of the alloyed samples (x =.25,.5, and.75) significantly decreased compared to MoSe2 and MoTe2 owing to point defect phonon scattering via anion substitution, which is verified by the Debye–Callaway model. A maximum zT of.0044 was obtained for MoTe2 sample at 773 K; however, the calculated quality factor B values of the samples with x =.75 and 1 at 773 K were almost identical, suggesting that a further enhancement of zT can be achieved by optimizing an nH of the Mo(Se0.25Te0.75)2 sample. [ABSTRACT FROM AUTHOR]

Band engineering is an effective strategy to improve the electronic transport properties of semiconductors. In thermoelectric materials research, density‐of‐states effective mass is an undoubted key factor in verifying the band engineering effect and establishing a strategy for enhancing thermoelectric performance. However, estimation of the effective mass is demanding or inaccurate depending on the methods taken. A simple equation is proposed, valid for all degeneracy: Log10 (md*T/300) = (2/3) Log10 (n) − (2/3) [20.3 − (0.00508 × |S|) + (1.58 × 0.967|S|)] that utilizes experimentally determined Seebeck coefficient (S) and carrier concentration (n) to determine the effective mass (md*) at a temperature (T). This straightforward equation, which gives an accurate analysis of the band modulation in terms of md*, is indispensable in designing thermoelectric materials of maximized performance. [ABSTRACT FROM AUTHOR]

The formation of secondary phases of NiTe2 and NbTe2 in p-type Bi0.5Sb1.5Te3 thermoelectric alloys was investigated through in situ phase separation by using the melt spinning process. Adding stoichiometric Ni, Nb, and Te in a solid-state synthesis process of Bi0.5Sb1.5Te3, followed by rapid solidification by melt spinning, successfully segregated NiTe2 and NbTe2 in the Bi0.5Sb1.5Te3 matrix. Since heterointerfaces of Bi0.5Sb1.5Te3 with NiTe2 and NbTe2 form potential barriers of 0.26 and 0.08 eV, respectively, a low energy carrier filtering effect can be expected; higher Seebeck coefficients and power factors were achieved for Bi0.5Sb1.5Te3(NiTe2)0.01 (250 μV/K and 3.15 mW/mK2), compared to those of Bi0.5Sb1.5Te3 (240 μV/K and 2.69 mW/mK2). However, there was no power factor increase for NbTe2 segregated samples. The decrease in thermal conductivity was seen due to the possible additional phonon scattering by the phase segregations. Consequently, zT at room temperature was enhanced to 0.98 and 0.94 for Bi0.5Sb1.5Te3(NiTe2)0.01 and Bi0.5Sb1.5Te3(NbTe2)0.01, respectively, compared to 0.79 for Bi0.5Sb1.5Te3. The carrier filtering effect induced by NiTe2 segregations with an interface potential barrier of 0.26 eV effectively increased the Seebeck coefficient and power factor, thus improving the zT of p-type Bi0.5Sb1.5Te3, while the interface potential barrier of 0.08 eV of NbTe2 segregation appeared to be too small to induce an effective carrier filtering effect. [ABSTRACT FROM AUTHOR]

Abstract: Taming electronic and thermal transport properties is the ultimate goal in the quest to achieve unprecedentedly high performance in thermoelectric (TE) materials. Most state‐of‐the‐art TE materials are inherently narrow bandgap semiconductors, which have an inevitable contribution from minority carriers, concurrently decreasing Seebeck coefficient and increasing thermal conductivity. Nevertheless, the restraint control of minority carrier transport is seldom considered as a key element to enhance the TE figure of merit (zT). Herein, it is verified that the localized dislocation arrays at grain boundaries enable the suppression of minority carrier contribution to electronic transport properties, resulting in an increase of the Seebeck coefficient and the carrier mobility in bismuth antimony tellurides. It is also suggested that the suppression of minority carriers via the generation of dislocation arrays at grain boundaries is an effective and noninvasive strategy to optimize overall electronic transport properties without sacrificing predominant characteristics of majority carriers in TE materials. [ABSTRACT FROM AUTHOR]

We present experimental evidence of enhancement of thermoelectric properties in tellurium (Te) nanoparticle-embedded bismuth antimony telluride (BiSbTe) alloys. Bi0.5Sb1.5Te3 films with a high density of Te particles of 10–20 nm size were prepared by growth of alternating multilayers of ultrathin Te and Bi0.5Sb1.5Te3. As the amount of Te nanoinclusions increased up to ∼15%, the Seebeck coefficient and thermoelectric power factor were increased. Based on the concept of band bending at heterointerfaces as a carrier energy filter, the energy relaxation calculation was made to confirm that the Te nanoinclusions result in a carrier energy filtering effect in p-type bismuth antimony telluride. In addition, thermal conductivities were reduced in the Te-embedded samples, permitting possible further enhancement of the thermoelectric figure of merit. The advantages of Te nanoinclusions in p-type Bi0.5Sb1.5Te3alloys on thermoelectric performance are experimentally realized by both electron- and phonon scattering. [ABSTRACT FROM AUTHOR]

One means of enhancing the performance of thermoelectric materials is to generate secondary nanoprecipitates of metallic or semiconducting properties in a thermoelectric matrix, to form proper band bending and, in turn, to induce a low-energy carrier filtering effect. However, forming nanocomposites is challenging, and proper band bending relationships with secondary phases are largely unknown. Herein, we investigate the in situ phase segregation behavior during melt spinning with various metal elements, including Ti, V, Nb, Mo, W, Ni, Pd, and Cu, in p-type Bi0.5Sb1.5Te3 (BST) thermoelectric alloys. The results showed that various metal chalcogenides were formed, which were related to the added metal elements as secondary phases. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the BST composite with various secondary phases were measured and compared with those of pristine BST alloys. Possible band alignments with the secondary phases are introduced, which could be utilized for further investigation of a possible carrier filtering effect when forming nanocomposites. [ABSTRACT FROM AUTHOR]

• SnSe 2- x Br x with x = 0, 0.004, 0.008, 0.01, and 0.02 were synthesized. • The valley degeneracy at conduction band minimum is increased by the Br doping. • The conduction band minimum also becomes flatter by the Br doping. • Power factor increased by increase in both carrier concentration and mobility. • Consequently, a thermoelectric figure of merit gradually improved with Br doping. [Display omitted] The effect of Br substitution on enhancing the thermoelectric properties of n -type layered SnSe 2 is investigated characterizing SnSe 2- x Br x synthesized with various Br contents (x = 0, 0.004, 0.008, 0.01, and 0.02). The electrical conductivity systematically increases with an increase in x owing to the simultaneous increase in both the carrier concentration (n) and mobility. As x increases, n increases by ~100 times; however, the magnitude of the Seebeck coefficient (| S|) decreases from 600 to 229 μV/K, resulting in an enhanced power factor at room temperature. The density functional theory calculations support that the valley degeneracy at the conduction band minimum increases with the Br substitution in SnSe 2 , while the conduction band minimum becomes flatter. This finding indicates that the increased density-of-state effective mass leads to the relatively large | S | even under a considerably increased n. Combined with the slight decrease in the thermal conductivity with an increase in x without significant additional phonon scattering, a thermoelectric figure of merit (zT) of 0.62 at 750 K is obtained for SnSe 1.98 Br 0.02 (x = 0.02), which is 50% higher than that for non-doped SnSe 2. [ABSTRACT FROM AUTHOR]

Nanostructuring is considered one of the key approaches to achieve highly efficient thermoelectric alloys by reducing thermal conductivity. In this study, we investigated the effect of oxide (ZnO and SnO2) nanolayers at the grain boundaries of polycrystalline In0.2Yb0.1Co4Sb12 skutterudites on their electrical and thermal transport properties. Skutterudite powders with oxide nanolayers were prepared by atomic layer deposition method, and the number of deposition cycles was varied to control the coating thickness. The coated powders were consolidated by spark plasma sintering. With increasing number of deposition cycle, the electrical conductivity gradually decreased, while the Seebeck coefficient changed insignificantly; this indicates that the carrier mobility decreased due to the oxide nanolayers. In contrast, the lattice thermal conductivity increased with an increase in the number of deposition cycles, demonstrating the reduction in phonon scattering by grain boundaries owing to the oxide nanolayers. Thus, we could easily control the thermoelectric properties of skutterudite materials through adjusting the oxide nanolayer by atomic layer deposition method. [ABSTRACT FROM AUTHOR]

Significant bipolar conduction of the carriers in Bi2Te3-based alloys occurs at high temperatures due to their narrow bandgaps. Therefore, at high temperatures, their Seebeck coefficients decrease, the bipolar thermal conductivities rapidly increase, and the thermoelectric figure of merit, zT, rapidly decreases. In this study, band modification of n-type Cu0.008Bi2(Te,Se)3 alloys by sulfur (S) doping, which could widen the bandgap, is investigated regarding carrier transport properties and bipolar thermal conductivity. The increase in bandgap by S doping is demonstrated by the Goldsmid–Sharp estimation. The bipolar conduction reduction is shown in the carrier transport characteristics and thermal conductivity. In addition, S doping induces an additional point-defect scattering of phonons, which decreases the lattice thermal conductivity. Thus, the total thermal conductivity of the S-doped sample is reduced. Despite the reduced power factor due to the unfavorable change in the conduction band, zT at high temperatures is increased by S doping with simultaneous reductions in bipolar and lattice thermal conductivity. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides have being actively studied on the account of their large density‐of‐state effective mass and low lattice thermal conductivity. Herein, thermoelectric and electrical transport properties of MoSe2–MoTe2 system are investigated. A series of Mo(Se1−xTex)2 (x = 0,.25,.5,.75, and 1) polycrystalline samples was synthesized by conventional solid‐state reaction. Single hexagonal phase was identified for each sample without secondary phase, confirming the formation of complete solid solutions between MoSe2 and MoTe2. The electrical conductivity and magnitude of the Seebeck coefficient increased simultaneously with increasing Te content x at high temperatures, with the power factor following the same trend. As results, the MoTe2 sample exhibited the maximum power factor of.014 mW/(m K2) at 823 K. The lattice thermal conductivities of the alloyed samples (x =.25,.5, and.75) significantly decreased compared to MoSe2 and MoTe2 owing to point defect phonon scattering via anion substitution, which is verified by the Debye–Callaway model. A maximum zT of.0044 was obtained for MoTe2 sample at 773 K; however, the calculated quality factor B values of the samples with x =.75 and 1 at 773 K were almost identical, suggesting that a further enhancement of zT can be achieved by optimizing an nH of the Mo(Se0.25Te0.75)2 sample. [ABSTRACT FROM AUTHOR]

FeSe 2 is a p -type semiconductor with a narrow band gap, which can be considered a potential thermoelectric material. Herin, the electrical and thermal properties of Cr-doped FeSe 2 , Fe 1-x Cr x Se 2 (x = 0, 0.03, 0.06, and 0.09), polycrystalline alloys are investigated. All compositions show single-phase marcasite structures of FeSe 2 with gradual decreases in lattice parameters with Cr doping x. With increasing x , the electrical conductivity gradually increases from 13 (x = 0) to 46 S/cm (x = 0.09), owing to a large increase in carrier concentration originated from the substitution of Cr2+ and Cr3+ at the Fe site. However, the magnitude of Seebeck coefficient decreases considerably at 300 K, resulting in decrease in power factor. In addition, the density-of-state effective mass decreases significantly from 6.0 m 0 –1.04 m 0. At 700 K, the decrease in Seebeck coefficient is less severe. Although the total and lattice thermal conductivity decrease at all temperatures owing to additional phonon scattering of the extrinsic Cr ions, a thermoelectric figure of merit, zT , generally decreases compared to that of the pristine sample due to power factor decrease at 300 K. Meanwhile, a slight increase of zT to 0.11 is observed for x = 0.06 at 700 K. • A series of Fe 1-x Cr x Se 2 (x = 0, 0.03, 0.06, and 0.09) alloys was investigated. • Carrier concentration increased by to doping of Cr2+ and Cr3+. • The density-of-state effective mass decreases significantly by Cr doping. • Lattice thermal conductivity decreased owing to additional phonon scattering. • A slight increase of thermoelectric figure of merit zT to 0.11 is observed for x = 0.06 at 700 K. [ABSTRACT FROM AUTHOR]

Cr 2 Se 3 is a layered narrow-bandgap semiconductor with a low lattice thermal conductivity of ∼1 W/mK, which can be considered as a potential thermoelectric material. A solid-solution alloy system with Cr 2 Te 3 can be designed to manipulate the electrical and thermal transport properties. In this study, a series of Cr 2 Se 3 -Cr 2 Te 3 solid-solution alloys (Cr 2 (Se 1- x Te x) 3 , x = 0, 0.33, 0.5, 0.67, 0.83, and 1) were synthesized, and their electrical and thermal transport properties were investigated. Regarding the electrical transport properties, the power factor (∼0.35 mW/mK2) of Cr 2 Se 3 gradually and significantly decreased as the Te content (x) increased owing to the significant decrease in the Seebeck coefficient that resulted from the large increase in the carrier concentration. Regarding the thermal transport properties, the total thermal conductivity increased with x as a result of the large increase in the electrical conductivity, despite the continuous decrease in the lattice thermal conductivity. Consequently, the thermoelectric figure of merit (zT ∼ 0.20) of Cr 2 Se 3 gradually and significantly decreased to 0.009 for Cr 2 Te 3 at 700 K; thus, no enhancement of zT was observed from the experimental results of simple solid-solution alloying. On the other hand, the thermoelectric quality factors of the solid-solution compositions for x = 0.33–0.83 were found to be enhanced compared to that of the Cr 2 Se 3 sample, implying that zT could be further enhanced by optimizing the carrier concentration. Indeed, enhanced zT values were estimated based on a single parabolic band model for the solid-solution compositions with x = 0.33–0.83 if the carrier concentration was optimized to ∼1019 cm−3, which was found to be owing to the increased nondegenerate and weighted mobility (inferring weaker carrier–phonon interaction). Therefore, it is suggested that the solid-solution alloying approach could provide a feasible strategy to enhance the thermoelectric performance by reducing carrier-phonon interaction when further combined with carrier concentration optimization. • A series of Cr 2 (Se 1- x Te x) 3 alloys (x = 0, 0.33, 0.5, 0.67, 0.83, and 1) was investigated. • Solid solution alloy is formed for the Cr 2 (Se 1- x Te x) 3 compositions. • Cr 2 (Se 1- x Te x) 3 showed the degraded thermoelectric properties with x increasing. • However, thermoelectric quality factors for x = 0.33–0.83 were found to be enhanced. • Enhanced thermoelectric properties are analyzed when carrier concentration optimized further. [ABSTRACT FROM AUTHOR]

Metal chalcogenide alloys are considered as electronic materials owing to their adjustable electrical properties either by doping or alloying. In this study, the electrical and thermal properties of the NiS 2 –NiSe 2 system are investigated by synthesizing Ni(S 1- x Se x) 2 (x = 0, 0.25, 0.5, 0.75, and 1.0) compositions. All samples exhibit pyrite-type cubic structures and form complete solid solution alloys. It is found that the NiS 2 –NiSe 2 system exhibits a wide spectrum of electrical characteristics; NiS 2 exhibits semiconducting conduction with low electrical conductivity σ of 7.8 S/cm and a carrier concentration of ∼1019 cm−3 at room temperature, whereas NiSe 2 exhibits metallic conduction with high σ of 11,600 S/cm and ∼1021 cm−3 carriers. As x of Ni(S 1- x Se x) 2 increased, the σ is gradually increased. On the other hand, the magnitude of Seebeck coefficient S is gradually decreased with x at 700 K. Thus, the optimized power factor (S 2∙ σ) of 0.10 mW/mK2 at 700 K is achieved for Ni(S 0.75 Se 0.25) 2 composition. Lattice thermal conductivities of the solid solution samples (x = 0.25, 0.5 and 0.75) range from 2.0 to 3.8 W/mK at 300 K, representing a reduction compared to those of NiS 2 and NiSe 2 (5.5 and 6.1 W/mK, respectively). Consequently, an enhanced thermoelectric performance was achieved in Ni(S 0.75 Se 0.25) 2 benefiting from an optimized solid solution alloying, with a maximum thermoelectric figure of merit of 0.020 at 700 K. [Display omitted] • A series of Ni(S 1- x Se x) 2 (x = 0, 0.25, 0.5, 0.75, and 1.0) was investigated. • NiS 2 and NiSe 2 exhibits semiconducting and metallic conduction, respectively. • The optimized power factor of 0.10 mW/mK2 is achieved for Ni(S 0.75 Se 0.25) 2. • Lattice thermal conductivities of the solid solution samples were reduced. • Optimized zT of 0.02 was obtained for Ni(S 0.75 Se 0.25) 2. [ABSTRACT FROM AUTHOR]

Herein, thermoelectric transport properties of lightly Pb-doped Bi 2- x Pb x Te 3 (x = 0, 0.0025, 0.005, and 0.01) alloys are investigated. Negative Seebeck coefficient (−169 μV/K) of the pristine Bi 2 Te 3 increases to −120 μV/K for x = 0.0025 at 300 K. As Pb further doped, positive Seebeck coefficients of 191 and 157 μV/K are measured for x = 0.005 and 0.01, respectively. P -type power factor increased to 2.32 mW/mK2 by the Pb doping for x = 0.01 at 300 K, compared with n -type power factor of 1.81 mW/mK2 of the pristine Bi 2 Te 3. The decrease in κ lat was observed for x = 0.01 due to additional phonon scattering by point defects. As results, p -type thermoelectric figure of merit zT of 0.42 for x = 0.01 is achieved compared with n -type zT of 0.35 for Bi 2 Te 3 at 300 K. The maximum p -type zT of 0.56 was obtained for Bi 1.99 Pb 0.01 Te 3 (x = 0.01). Therefore, a relative high p -type zT value was successfully achieved by the slight Pb doping in Bi 2 Te 3 by carrier type change from n -type to p -type. [ABSTRACT FROM AUTHOR]

Ti 2 FeNiSb 2 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 Ti 2 FeNiSb 2 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 Ti 2 Fe 0.9 Co 0.1 NiSb 2 is achieved, which is approximately six times higher than that of the pristine Ti 2 FeNiSb 2. The thermoelectric performance of Ti 2 FeNiSb 2 can be improved by selective band engineering to bypass the Seebeck coefficient-electrical conductivity trade-off relation from atomic-site targeted doping. • Atomic site-targeted doping can fine-tune band parameters of double half-Heusler. • Doping at different atomic sites has a different impact on the phonon scattering. • Doping Co at Fe-sites of Ti 2 FeNiSb 2 improves zT of pristine Ti 2 FeNiSb 2 by six times. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides have gained renewed attention as promising thermoelectric materials primarily because of their unique structures and superior electronic properties. In this study, we investigate the electrical transport properties of a series of Hf(Se,Te) 2 samples (Hf(Se x Te 1- x) 2 , x = 0, 0.025, 0.25, 0.375, 0.5, and 1). All the samples form a single phase of a complete solid solution, displaying a wide variety of electrical properties based on the evolution of the composition. HfTe 2 exhibits metallic conduction with very high electrical conductivity of ~1600 S/cm, whereas HfSe 2 exhibits semiconducting conduction with very low electrical conductivity of 0.33 S/cm at room temperature. In contrast, the Seebeck coefficient of the HfTe 2 sample is as low as 17 μV/K, whereas that of HfSe 2 approaches 730 μV/K. Therefore, the power factor for HfTe 2 represents a much higher value of 0.24 mW/mK2 when compared with 0.01 mW/mK2 for HfSe 2 at 600 K. The superior electrical transport properties of HfTe 2 are primarily caused by its high carrier concentration of 1021 cm−3 and high density-of-state effective mass of 0.91 m 0. A comparison of the electronic band dispersion between HfSe 2 and HfTe 2 calculated using the density functional theory indicates that the dispersions of the conduction and valence bands seem to remain unchanged: HfSe 2 exhibits a finite band gap, whereas HfTe 2 exhibits no or a very small band gap. • A series of Hf(Te 1−x Se x) 2 (x = 0, 0.025, 0.25, 0.375, 0.5, and 1) was investigated. • Complete solid solution is formed throughout whole HfSe 2 -HfTe 2 composition. • HfSe 2 -HfTe 2 system provides a wide variety of electrical transport properties from semiconducting to metallic. • Band dispersions were calculated for HfSe 2 and HfTe 2 using the density functional theory. • Power factor for HfTe 2 exhibits 0.24 mW/mK at 600 K. [ABSTRACT FROM AUTHOR]