P-type Thermoelectric Materials Research Articles

Controlling the thermoelectric properties of organo-metallic coordination polymers through backbone geometry.

Poly(nickel-benzene-1,2,4,5-tetrakis(thiolate)) (Ni-btt), an organometallic coordination polymer (OMCP) characterized by the coordination between benzene-1,2,4,5-tetrakis(thiolate) (btt) and Ni2+ ions, has been recognized as a promising p-type thermoelectric material. In this study, we employed a constitutional isomer based on benzene-1,2,3,4-tetrakis(thiolate) (ibtt) to generate the corresponding isomeric polymer, poly(nickel-benzene-1,2,3,4-tetrakis(thiolate)) (Ni-ibtt). Comparative analysis of Ni-ibtt and Ni-btt reveals several common infrared (IR) and Raman features attributed to their similar square-planar nickel-sulfur (Ni-S) coordination. Nevertheless, these two polymer isomers exhibit substantially different backbone geometries. Ni-btt possesses a linear backbone, whereas Ni-ibtt exhibits a more undulating, zig-zag-like structure. Consequently, Ni-ibtt demonstrates slightly higher solubility and an increased bandgap in comparison to Ni-btt. The most noteworthy dissimilarity, however, manifests in their thermoelectric properties. While Ni-btt exhibits p-type behavior, Ni-ibtt demonstrates n-type carrier characteristics. This intriguing divergence prompted further investigation into the influence of OMCP backbone geometry on the electronic structure and, particularly, the thermoelectric properties of these materials.

Thermoelectric properties of Gd and Se double substituted tetrahedrite.

The compound Cu12Sb4S13, known as tetrahedrite, is an eco-friendly p-type thermoelectric material with earth-abundant, low-cost, and less toxic constituents. This contemporary work studied the thermoelectric properties of Gd and Se double-substituted tetrahedrites. The samples with nominal composition Cu11.95Gd0.05Sb4S13-xSex (where x = 0, 0.2, 0.4, 0.6, and 0.8) were prepared using the solid-state synthesis and sintered using high vacuum hot pressing. The structural analysis using X-ray diffraction revealed a successful tetrahedrite phase formation, and the systematic increase of lattice parameters with the selenium content (x) indicated successful Se substitution. The electron probe microanalysis revealed the presence of secondary phases Cu3SbS4, CuSbS2, and CuGdS2. The Raman spectroscopy showed a weakening Sb-S/Se bond with increased Se content in the samples. The +3 and -2 oxidation states of Gd and Se, respectively, were confirmed from the XPS study. Gd3+, a higher valence substituent at the Cu+/Cu2+ tetrahedral site, helped reduce the carrier concentration. On the other hand, the isoelectronic substitution of Se2- for S2- enhanced the thermopower and power factor by introducing resonant energy states near the Fermi level. Consequently, a maximum power factor of ∼1.35 (±0.08) mW m-1 K-2 at ∼729 K was obtained for the sample x = 0.4. The sample x = 0.4 also exhibited the lowest thermal conductivity ∼ 1.18 (±0.04) W m-1 K-1 at 729 K. The Callaway model indicates that the lowering in the lattice thermal part of conductivity of this sample is due to the combined effect of point defect and Umklapp scattering. The simultaneous improvement of carrier concentration and thermal conductivity resulted in a relatively high zT of ∼0.83 (±0.09) in the x = 0.4 sample.

Production of (Fe,Co)Si2 and (Fe.Mn)Si2 Thermoelectric Materials by Spark Plasma Sintering

In this study, FeSi2 bulk specimens were prepared by mechanical alloying, spark plasma sintering, and subsequent annealing. The annealed FeSi2 bulk specimens consisted of the β-FeSi2 phase and exhibited high Seebeck coefficient values. The maximum Seebeck coefficient of 356 μVK−1 was achieved in the FeSi2 bulk specimen annealed at 1173 K for 6 h. However, the power factor of the FeSi2 bulk specimen was quite small due to its high electrical resistivity, and a drastic improvement is required. Therefore, Mn- and Co-substituted specimens, Fe1−xMnxSi2 (x = 0.2–0.8) and Fe1−xCoxSi2 (x = 0.2–0.8), were produced, and their thermoelectric properties were evaluated. The Mn- and Co-substituted specimens exhibited lower electrical resistivity and a higher power factor than the FeSi2 bulk specimen. The Fe1−xMnxSi2 (x = 0.2–0.8) bulk specimens were p-type thermoelectric materials, and a Seebeck coefficient of 262 μVK−1 and a power factor of 339 μWm−1K−2 were achieved in the Fe0.94Mn0.06Si2 bulk specimen. On the other hand, the Fe1−xCoxSi2 (x = 0.2–0.8) bulk specimens were n-type thermoelectric materials, and a Seebeck coefficient of −180 μVK−1 and a power factor of 667 μWm−1K−2 were achieved in the Fe0.96Co0.04Si2 bulk specimen.

Band Engineering Through Pb-Doping of Nanocrystal Building Blocks to Enhance Thermoelectric Performance in Cu3SbSe4.

Developing cost-effective and high-performance thermoelectric (TE) materials to assemble efficient TE devices presents a multitude of challenges and opportunities. Cu3SbSe4 is a promising p-type TE material based on relatively earth abundant elements. However, the challenge lies in its poor electrical conductivity. Herein, an efficient and scalable solution-based approach is developed to synthesize high-quality Cu3SbSe4 nanocrystals doped with Pb at the Sb site. After ligand displacement and annealing treatments, the dried powders are consolidated into dense pellets, and their TE properties are investigated. Pb doping effectively increases the charge carrier concentration, resulting in a significant increase in electrical conductivity, while the Seebeck coefficients remain consistently high. The calculated band structure shows that Pb doping induces band convergence, thereby increasing the effective mass. Furthermore, the large ionic radius of Pb2+ results in the generation of additional point and plane defects and interphases, dramatically enhancing phonon scattering, which significantly decreases the lattice thermal conductivity at high temperatures. Overall, a maximum figure of merit (zTmax) ≈ 0.85 at 653 K is obtained in Cu3Sb0.97Pb0.03Se4. This represents a 1.6-fold increase compared to the undoped sample and exceeds most doped Cu3SbSe4-based materials produced by solid-state, demonstrating advantages of versatility and cost-effectiveness using a solution-based technology.

Enhancement of the thermoelectric performance of half-metallic full-Heusler Mn2VAl alloys via antisite defect engineering and Si partial substitution

A half-metallic full-Heusler Mn2VAl alloy is a potential p-type thermoelectric material that can directly generate electricity from waste heat via the Seebeck effect. For practical use, the Seebeck coefficient S of Mn2VAl should be increased while maintaining a high electrical conductivity σ from its half-metallic character. Herein, we achieved this objective through antisite defect engineering. Theoretically, it was predicted that the S was maximized by regulating partial density of states of majority-spin sp-electrons through the control of the fraction of antisite defect, fAD, between V and Al atoms in Mn2VAl. Experimentally, a significant increase in S and a slight decrease in σ were observed for an Mn2VAl sample with an optimal fAD = 33%, enhancing the thermoelectric power factor PF by 2.7 times from an Mn2VAl sample with fAD = 14%. Furthermore, we combined the antisite defect engineering with a partial substitution method. An Mn2V(Al0.96Si0.04) sample with fAD = 33% exhibited the highest PF = 4.5 × 10−4 W·m−1·K−2 at 767 K among the samples. The maximum dimensionless figure-of-merit zT of the Mn2V(Al0.96Si0.04) sample with fAD = 33% was measured to be 3.4 × 10−2 at 767 K, which is the highest among the p-type half-metallic full-Heusler alloys.

Rattling-like behavior and band convergence induced ultra-low lattice thermal conductivity in MgAl2Te4 monolayer

Inspired by the excellent stability exhibited by experimentally synthesized two-dimensional (2D) MoSi2N4 layered material, the thermal and electronic transport, and thermoelectric (TE) properties of MgAl2Te4 monolayer are systematically investigated using the First-principles calculations and Boltzmann transport theory. The mechanical stability, dynamic stability, and thermal stability (900 K) of the MgAl2Te4 monolayer are demonstrated, respectively. The MgAl2Te4 monolayer exhibits a bandgap of 1.35 eV using the HSE06 functional in combination with spin-orbit coupling (SOC) effect. Band convergence in the valence band is favorable to improve the thermoelectric properties. The rattling thermal damping effect caused by the weak bonding of MgTe bonds in MgAl2Te4 monolayer leads to ultra-low lattice thermal conductivity (0.95/0.38 W/(m·K)@300 K along the x-/y-direction), which is further demonstrated by the phonon group velocities, phonon relaxation time, Grüneisen parameters, and scattering mechanisms. The optimal zT of 3.28 at 900 K is achieved for the p-type MgAl2Te4 monolayer, showing the great promising prospect for the excellent p-type thermoelectric material. Our current work not only reveals the underlying mechanisms responsible for the excellent TE properties, but also elaborates on the promising thermoelectric application of MgAl2Te4 monolayer material at high temperature.

High-throughput deformation potential and electrical transport calculations

The deformation potential plays an important role in electrical transport properties, but in the context of high-throughput searches requires a consistent and readily computable reference level. Here, we design a high-throughput method for calculating the deformation potential for semiconductors in the MatHub-3d database. The deformation potential is obtained from the volume-dependent band edge (valence band maximum and conduction band minimum) variations with respect to the reference level. In order to adapt the calculation of reference level to a high-throughput manner, the average value of the first valence electron energy band associated with each compound is used as the reference level. Deformation potentials for 11,993 materials are calculated using the above-mentioned method. By considering the calculated deformation potentials, electronic structures, and bulk moduli, 9957 compounds with converged electrical transport properties are obtained. 332 promising p-type thermoelectric materials, and 321 n-type entries are then proposed. Among them, 156 compounds are screened to having both potentially good n- and p-type thermoelectric transport properties. The band structures and chemical bonding information for several typical compounds are further presented to reveal favorable band and bonding features for thermoelectrics.

Enhancing Thermoelectric Performance of CuInTe2 via Trace Ag Doping at Indium Sites.

Thermoelectric technology can be utilized to directly convert waste heat into electricity, aiming at energy harvesting in an environmentally friendly manner. As a promising p-type thermoelectric material, CuInTe2 possesses a high inherent lattice thermal conductivity, which limits the practical implementation in the field of thermoelectricity. Herein, through the combination of vacuum melting and annealing along with hot-pressure sintering techniques, we demonstrated that CuIn0.95Ag0.05Te2 thermoelectric materials with trace Ag doping can exhibit a notably high Seebeck coefficient of 614 μV/K, arising from the high density-of-states effective mass and reduced carrier concentration. Owing to the diminished lattice thermal conductivity derived from Umklapp scattering induced by point defects and dislocation, stemming from the trace Ag doping at In sites rather than Cu sites, CuIn0.95Ag0.05Te2 exhibited a maximum figure of merit (ZT) of 1.38 at 823 K, an 18% enhancement over pristine CuInTe2, leading to a maximum average ZT of 0.67 across temperatures ranging from 303 to 823 K. In essence, our work underscores the efficacy of doping engineering and point defects in tailoring the thermoelectric performance of CuInTe2-based materials. This study not only contributes to advancing the fundamental understanding of thermoelectric enhancement but also lays out a practical pathway toward the realization of high-performance CuInTe2-based thermoelectric materials.

Realizing the Ultralow Lattice Thermal Conductivity of Cu3SbSe4 Compound via Sulfur Alloying Effect.

Cu3SbSe4 is a potential p-type thermoelectric material, distinguished by its earth-abundant, inexpensive, innocuous, and environmentally friendly components. Nonetheless, the thermoelectric performance is poor and remains subpar. Herein, the electrical and thermal transport properties of Cu3SbSe4 were synergistically optimized by S alloying. Firstly, S alloying widened the band gap, effectively alleviating the bipolar effect. Additionally, the substitution of S in the lattice significantly increased the carrier effective mass, leading to a large Seebeck coefficient of ~730 μVK-1. Moreover, S alloying yielded point defect and Umklapp scattering to significantly depress the lattice thermal conductivity, and thus brought about an ultralow κlat ~0.50 Wm-1K-1 at 673 K in the solid solution. Consequently, multiple effects induced by S alloying enhanced the thermoelectric performance of the Cu3SbSe4-Cu3SbS4 solid solution, resulting in a maximum ZT value of ~0.72 at 673 K for the Cu3SbSe2.8S1.2 sample, which was ~44% higher than that of pristine Cu3SbSe4. This work offers direction on improving the comprehensive TE in solid solutions via elemental alloying.

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.

Power factor enhancement of β-Zn4Sb3-InSb composites via arrays of p-n junction: Mixing p-type and n-type thermoelectric materials

The lead-free and abundantly available nature of β-Zn4Sb3 makes it a promising thermoelectric material for mid-high temperature applications. We produce composites by embedding 1 wt %, 3 wt %, and 5 wt % of n-type InSb into the p-type β-Zn4Sb3 host, enhancing both electrical conductivity and thermopower. At 600 K, the electrical resistivity decreases to 55 μΩ-m from 71 μΩ-m for the β-Zn4Sb3 host. Surprisingly, the thermopower of the β-Zn4Sb3/3 wt % InSb composite increases to 209 μV/K from 180 μV/K for the β-Zn4Sb3 host, contrary to expectations. This enhancement can be attributed to p-n junctions between the p-type β-Zn4Sb3 and n-type InSb. The power factor of the β-Zn4Sb3/3 wt % InSb composite increased to 787 μW/mK2 from 452 μW/mK2 for the β-Zn4Sb3 host. Despite higher thermal conductivity, the β-Zn4Sb3/3 wt % InSb composite achieved the highest zT value of ∼0.67 at around 600 K, 67.5 % higher than the β-Zn4Sb3 host's zT value of 0.40.

Thermoelectric properties of cement composite analogues from first principles calculations

Buildings are responsible for a considerable fraction of the energy wasted globally every year, and as a result, excess carbon emissions. While heat is lost directly in colder months and climates, resulting in increased heating loads, in hot climates cooling and ventilation is required. One avenue towards improving the energy efficiency of buildings is to integrate thermoelectric devices and materials within the fabric of the building to exploit the temperature gradient between the inside and outside to do useful work. Cement-based materials are ubiquitous in modern buildings and present an interesting opportunity to be functionalized. We present a systematic investigation of the electronic transport coefficients relevant to the thermoelectric materials of the calcium silicate hydrate (C-S-H) gel analogue, tobermorite, using Density Functional Theory calculations with the Boltzmann transport method. The calculated values of the Seebeck coefficient are within the typical magnitude (200-600 μ V/K) indicative of a good thermoelectric material. The tobermorite models are predicted to be intrinsically p-type thermoelectric material because of the presence of large concentration of the Si-O tetrahedra sites. The calculated electronic figure of merit, ZT, for the tobermorite models have their optimal values of 0.983 at (400 K and 1017 cm−3) for tobermorite 9 Å, 0.985 at (400 K and 1017 cm−3) for tobermorite 11 Å and 1.20 at (225 K and 1019 cm−3) for tobermorite 14 Å, respectively.

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.

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.

High-performance Sb2Si2Te6 thermoelectric device

High-performance thermoelectric (TE) devices are promising for waste-heat recovery and power generation. Recently, Sb2Si2Te6 has been demonstrated as a promising p-type TE material with high performance and low cost. However, Sb2Si2Te6-based TE devices have not yet been fabricated. The performance of TE devices depends on not only TE materials, but also electrode materials and inner interfaces. Herein, we utilize the high throughput strategy to screen the appropriate electrode material and find that cobalt exhibits a low contact resistance (2.47 μΩ cm−2) and a high shear strength (18.03 MPa). Furthermore, we successfully fabricate one eight-couple Sb2Si1.99Ge0.01Te6 (p-type)/Yb0.3Co4Sb12 (n-type) TE module with optimized geometric parameters by the finite element method. The module exhibits a high output power density (0.92 W cm−2) and a decent energy conversion efficiency (4.2%) under a temperature difference of 500 K. Our studies will promote further development of Sb2Si2Te6 materials and Sb2Si2Te6-based devices.

Change of Conduction Mechanism in Polymer/Single Wall Carbon Nanotube Composites upon Introduction of Ionic Liquids and Their Investigation by Transient Absorption Spectroscopy: Implication for Thermoelectric Applications.

Polymer composites based on polycarbonate (PC) and polyether ether ketone (PEEK) filled with single-walled carbon nanotubes (SWCNTs, 0.5-2.0 wt %) were melt-mixed to investigate their suitability for thermoelectric applications. Both types of polymer composites exhibited positive Seebeck coefficients (S), indicative for p-type thermoelectric materials. As an additive to improve the thermoelectric performance, three different ionic liquids (ILs), specifically THTDPCl, BMIMPF6, and OMIMCl, were added with the aim to change the thermoelectric conduction type of the composites from p-type to n-type. It was found that in both composite types, among the three ILs employed, only the phosphonium-based IL THTDPCl was able to activate the p- to n-type switching. Moreover, it is revealed that for the thermoelectric parameters and performance, the SWCNT:lL ratio plays a role. In the selected systems, S-values between 61.3 μV/K (PEEK/0.75 wt % SWCNT) and -37.1 μV/K (PEEK/0.75 wt % SWCNT + 3 wt % THTDPCl) were reached. In order to shed light on the physical origins of the thermoelectric properties, the PC-based composites were studied using ultrafast laser time-resolved transient absorption spectroscopy (TAS). The TAS studies revealed that the introduction of ILs in the developed PC/CNT composites leads to the formation of biexcitons when compared to the IL-free composites. Moreover, no direct correlation between S and exciton lifetimes was found for the IL-containing composites. Instead, the exciton lifetime decreases while the conductivity seems to increase due to the availability of more free-charge carriers in the polymer matrix.

Improved High Temperature Thermoelectric Properties in Misfit Ca3Co4O9 by Thermal Annealing

Ca3Co4O9, a p-type thermoelectric material based on transition-metal oxides, has garnered significant interest due to its potential in thermoelectric applications. Its unique misfit-layered crystal structure contributes to low thermal conductivity and a high Seebeck coefficient, leading to a thermoelectric figure of merit (zT) of ≥1 at 1000 K. Conventionally, it has been believed that thermopower reaches its upper limit above 200 K. However, our thermopower measurements on polycrystalline Ca3Co4O9 samples have revealed an unexpected increase in thermopower above 380 K. In this study, we investigate the effects of high oxygen pressure annealing on Ca3Co4O9 and provide an explanation based on the mixed oxide states of cobalt and carrier hopping. Our results demonstrate that annealing induces modifications in the defect chemistry of Ca3Co4O9, leading to a decrease in electron hopping probability and the emergence of a thermal activation-like behavior in thermopower. These findings carry significant implications for the design and optimization of thermoelectric materials based on misfit cobaltates, opening new avenues for enhanced thermoelectric performance.

Neutron-irradiated effect on the thermoelectric properties of Bi2Te3-based thermoelectric leg

Thermoelectric (TE) materials working in radioisotope thermoelectric generators are irradiated by neutrons throughout its service; thus, investigating the neutron irradiation stability of TE devices is necessary. Herein, the influence of neutron irradiation with fluences of 4.56 × 1010 and 1 × 1013 n/cm2 by pulsed neutron reactor on the electrical and thermal transport properties of n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 thermoelectric alloys prepared by cold-pressing and molding is investigated. After neutron irradiation, the properties of thermoelectric materials fluctuate, which is related to the material type and irradiation fluence. Different from p-type thermoelectric materials, neutron irradiation has a positive effect on n-type Bi2Te2.7Se0.3 materials. This result might be due to the increase of carrier mobility and the optimization of electrical conductivity. Afterward, the effects of p-type and n-type TE devices with different treatments on the output performance of TE devices are further discussed. The positive and negative effects caused by irradiation can cancel each other to a certain extent. For TE devices paired with p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.7Se0.3 thermoelectric legs, the generated power and conversion efficiency are stable after neutron irradiation.

Colossal figure of merit and compelling HER catalytic activity of holey graphyne

Herein, we have conducted a comprehensive study to uncover the thermal transport properties and hydrogen evolution reaction catalytic activity of recently synthesized holey graphyne. Our findings disclose that holey graphyne has a direct bandgap of 1.00 eV using the HSE06 exchange–correlation functional. The absence of imaginary phonon frequencies in the phonon dispersion ensures its dynamic stability. The formation energy of holey graphyne turns out to be − 8.46 eV/atom, comparable to graphene (− 9.22 eV/atom) and h-BN (− 8.80 eV/atom). At 300 K, the Seebeck coefficient is as high as 700 μV/K at a carrier concentration of 1 × 1010 cm-2. The predicted room temperature lattice thermal conductivity (κl) of 29.3 W/mK is substantially lower than graphene (3000 W/mK) and fourfold smaller than C3N (128 W/mK). At around 335 nm thickness, the room temperature κl suppresses by 25%. The calculated p-type figure of merit (ZT) reaches a maximum of 1.50 at 300 K, higher than that of holey graphene (ZT = 1.13), γ-graphyne (ZT = 0.48), and pristine graphene (ZT = 0.55 × 10–3). It further scales up to 3.36 at 600 K. Such colossal ZT values make holey graphyne an appealing p-type thermoelectric material. Besides that, holey graphyne is a potential HER catalyst with a low overpotential of 0.20 eV, which further reduces to 0.03 eV at 2% compressive strain.

Effects of Sn and In Double-Doping on the Thermoelectric Performance of Cu3Sb1-x-ySnxInyS4 Famatinites

Famatinite (Cu3SbS4 ) is a promising p-type thermoelectric material because of its low lattice thermal conductivity and high Seebeck coefficient. In this study, famatinite powders, double-doped with Sn (a BIV group element) and In (a BIII group element) to give Cu3Sb1-x-ySnxInyS4 (0.02 ≤ x ≤ 0.12 and 0.06 ≤ y ≤ 0.10), were synthesized by mechanical alloying and then consolidated by hot pressing. Phase analysis and microstructure observations were conducted over a range of doping levels, and the charge transport parameters and thermoelectric properties were evaluated. Except for the specimen with y = 0.10, in which the secondary phase CuInS2 was found, all the specimens exhibited a tetragonal famatinite phase without secondary phases. The Sn/In double doping increased the unit cell a-axis to 0.5387–0.5389 nm and changed the c-axis to 1.0744–1.0752 nm. As the temperature increased, the electrical conductivity decreased while the Seebeck coefficient increased, which indicates that the Sn/In double-doped famatinites have degenerate semiconductor characteristics. With increasing Sn and In content, the carrier concentration increased, so that the electrical conductivity increased and the Seebeck coefficient decreased. Cu3Sb0.80Sn0.12In0.08S4 exhibited the highest power factor, 0.87 mW m-1 K-2 at 623 K, with greatly increased thermal conductivity. Cu3Sb0.86Sn0.08In0.06S4 showed the highest value for the dimensionless figure of merit, ZT = 0.53 at 623 K, with a power factor of 0.78 mW m-1 K-2 and thermal conductivity of 0.90 W m-1 K-1.