Total Thermal Conductivity Research Articles

Cu-doping boosts the thermoelectric properties of layered compound LaOBiS2 with weak anisotropy

Layered compounds like Bi2Te3 and SnSe are attracting great interest for applications in thermoelectric devices, mainly due to their low lattice thermal conductivity from large anharmonicity. Herein, we report the thermoelectric properties of the quaternary layered compound LaOBiS2, which is a n-type semiconductor constructed by stacking of fluorite-type [LaO]+ layers and rock-salt-type [BiS2]- layers. Our results reveal that the as-sintered LaOBiS2 sample features weak anisotropy due to the almost random arrangement of crystalline grains with nonpreferred-orientation growth. The pristine LaOBiS2 has high intrinsic electrical conductivity and low Seebeck coefficient as a result of a high electron concentration (n = 3.25 ×1020 cm−3, 300 K) from anionic vacancy. Meanwhile, the total thermal conductivity of LaOBiS2 is as low as 1.10 W m−1 K−1 at 873 K. Cu-doping improve the overall thermoelectric properties, which induces a decrease in both electrical conductivity and thermal conductivity. The maximum zT is 0.24 at 873 K for the sample with dopant Cu of 1 %, indicating a 33 % increase compared with pristine LaOBiS2. Our work demonstrates that constructing semiconductors by functional building blocks is an effective approach to design thermoelectric compounds.

Effect of Annealing on Thermoelectric Properties of Crystals Yb<sub>x</sub>Bi<sub>2-x</sub>Te<sub>3</sub>

The work is devoted to the study of the thermoelectric properties of solid crystal Yb_xBi_2-xTe₃. In the work presents the results of studies of the thermoelectric properties of Yb_xBi_2-xTe₃ (х≤0.10) solid solutions before and after annealing in the temperature range (300-580)K. Regularities of changes in the electrical conductivity, Seebeck coefficient and total thermal conductivity of the samples depending on the content of ytterbium (Yb) are established. Dependences of electrical conductivity, Seebeck coefficient, thermal conductivity on temperature for the crystal under study are plotted. Temperature curves were recorded using a Termoscan-2 low-frequency temperature recorder at a heating rate of 283 K/ min. Temperature measurements of phase transformations were carried out with combined chromel-alumel thermocouples. Studies of conductivity σ, thermoelectric power (S). were carried out by the four-probe method at direct current in the temperature range of 300-600 K. Ohmic contacts were applied using alloys. It has been established that the optimal combination of these thermoelectric characteristics is achieved for the compositions x = 0.1, which are characterized by the maximum thermoelectric index (ZT=0.87) of the figure of merit in the temperature range of 420-500 K after annealing at 500 K for τ=240 hours. It was revealed that the Yb_xBi_2-xTe₃ systems under study are n-type semiconductor thermoelectric materials in the temperature range of 300-600K.

Significantly reduced lattice thermal conductivity with anharmonic lattice vibrations and band edge effect in electronic thermal conductivity in Ag2S1-xSex (0 ≤ x ≤ 0.6)

The composition dependence of the unusual behaviors in electronic and lattice thermal conductivity, κele and κlat, in Ag2S1-xSex (x = 0–0.6 in steps of 0.1, 300 K) is investigated in detail by means of precise electron and heat transport properties measurement, synchrotron X-ray crystal structure and electron density distribution analyses, and sound velocity measurement. We reveal that the κele of Ag2S1-xSex is strongly affected by the fine electronic structure of the conduction band edge near the chemical potential and the thermoelectric motive force; therefore, these effects make the κele of Ag2S1-xSe far different from that calculated by the Wiedemann–Franz law, κele = L0σT, with the Lorentz number L0 = π2kB2/(3e2). It is also clearly demonstrated that the κlat of Ag2S1-xSex is greatly reduced by anharmonic lattice vibrations and that the magnitude of κlat is quantitatively reproduced by an equation representing the thermal conductivity under the strongest scattering limit. The κlat decreases with increasing x and saturates at 0.4 W m−1 K−1 at x ≥ 0.4. This is caused by the increasing anharmonic lattice vibrations with x, and its saturating behavior is determined by the strongest scattering limit. On the other hand, a negligibly small κele at x = 0 turns out to be non-trivial at x ≥ 0.4 owing to the increasing carrier density with x, most likely contributed by the increasing interstitial Ag defects. Consequently, the total thermal conductivity of Ag2S1−xSex becomes minimum not at x = 0.5 (composition of the maximum structure entropy) but at x = 0.3.

Anharmonic phonon renormalization and two-channel thermal transport in SrTiO3 using full temperature-dependent interatomic force constant

The microscopic mechanism of lattice thermal conductivity of SrTiO3 is investigated by full temperature-dependent anharmonic phonon renormalization and two-channel thermal transport. The contribution of normal phonon is calculated by the Boltzmann transport equation, while the contribution of diffusion phonon is treated by random-walk diffusion theory and wave-like tunneling of phonon. Based on the anharmonic phonon renormalization, the full temperature-dependent interatomic force constant is utilized to calculate the thermal conductivity of normal phonon and diffusion phonon. With the combined inclusion of normal phonon and diffusion phonon, our work successfully reproduces the experimental thermal conductivity of SrTiO3 on top of full temperature-dependent anharmonic phonon renormalization. Our results show that the anharmonic phonon renormalization (a) strongly hardens the acoustic branch and softens the optical branch, (b) suppresses the weighted phase space of low-frequency phonon modes, reducing the coupling between acoustic and optical phonons, and (c) diminishes the strength of three-phonon scattering and four-phonon scattering, enlarging the lattice thermal conductivity. The anharmonic phonon renormalization plays a significant role in the thermal transport process of SrTiO3, and the diffusion phonon transport also makes an important contribution to the total thermal conductivity. The methodology may be used to resolve the discrepancies between experimental and theoretical thermal conductivity.

Design and spraying-preparation of the gradient coatings with various diameters and contents of SiO2 nano-particles for the enhanced anti-impact and thermal insulation performance

Composites used in aircraft are vulnerable to mechanical and thermal damage during particle impact at high speeds. In this paper, a series of gradient polyurethane silica coatings with different silica particle sizes and concentration gradients were prepared on epoxy resin matrix composites by pneumatic spraying process. The results of corundum impact and thermal insulation performance experiments indicated that multi-layer gradient coatings improved the particle impact resistance and thermal insulation. The damage was reduced to <1 % of surface damage area and thickness loss under the protection of enhanced gradient coatings, showing excellent particle impact resistance. Under unidirectional heating conditions, the temperature difference between the heating plate and the sample surface was four times that of the unprotected sample, from 2.2 °C to 9.4 °C, and the total thermal conductivity of the protected sample was reduced by 91.73 %. The coatings remained intact under high-speed particle collision of 300 A plasma flow, which verified the protection performance of the coatings simulating the situation that the coatings were impacted by particles and heated simultaneously. The as-prepared gradient coatings can effectively enhance the anti-impact and thermal insulation performance of composites, exhibiting wide application prospects.

Microwave synthesis and excellent thermoelectric performances of Yb-filled CoSb3 skutterudites

The nearly single-phase Yb-filled and Te-doped YbxCo4Sb11.5Te0.5 are prepared by microwave, and the skutterudites are further densification by spark plasma sintering. The experimental results show that Yb filling and Te doping further improve the electrical properties and confine the mean free path of phonons, resulting in a significant reduction the lattice thermal conductivity. And the maximum power factor of Yb0.2Co4Sb11.5Te0.5 is 4364.45 μWm−1K−2 at 675 K. Analysis believes that the resonance scattering root from Yb filling and the defect scattering and stress field fluctuation introduced by Te doping can effectively limit the thermal transport performance. In 300∼775 K, the total thermal conductivity of Yb0.2Co4Sb11.5Te0.5 is 2.68∼3.74 Wm−1K − 1, and the maximum ZT is 1.25 at 775 K, revealing Yb filling and Te doping improve the electrical properties and reduce the thermal conductivity of by limiting the mean free path of phonons.

Enhanced thermoelectric performance of Cu2Se realized by Ag2S doping

In this paper, Cu2Se samples doped with different concentrations of Ag2S were prepared by mechanical alloying and spark plasma sintering. Ag and S elements diffused during the preparation process and appeared aggregation in EDS mapping images. AgCuSe impurity phase can be observed in Cu2Se samples after Ag2S doping. Because of the enhanced scattering of the low- and mid-frequency phonons by AgCuSe nano inclusion, the total thermal conductivity of the Ag2S doped samples exhibits a significant decrease. Additionally, the diffusion and substitution of S can efficiently impede the formation of Cu vacancies. Ag ions can also fill the Cu vacancies, leading to the decreasing carrier concentration. Finally, the thermoelectric property is improved and the maximum ZT value ∼1.5 is achieved at 820 K in Cu2Se/ 2% Ag2S, which is about 1.5 times of the undoped Cu2Se sample.

Phonon transport in Cu2GeSe3 : Effects of spin-orbit coupling and higher-order phonon-phonon scattering

Much attention has been focused on understanding the mechanism of low lattice thermal conductivity in Cu-based diamondlike thermoelectric compounds. For ${\mathrm{Cu}}_{2}\mathrm{Ge}{\mathrm{Se}}_{3}$, the underlying origin of low lattice thermal conductivity remains to be clarified. In this work, the first-principles calculations are employed to systematically investigate the effects of spin-orbit coupling, higher-order phonon-phonon scattering, phonon wavelike tunneling, temperature-induced renormalization of phonon and phonon-phonon interaction, and volumetric expanse on the phonon transport of ${\mathrm{Cu}}_{2}\mathrm{Ge}{\mathrm{Se}}_{3}$. We show that the spin-orbit coupling results in no detectable change on the phonon frequencies, compared with those obtained without spin-orbit coupling, while it induces slight increase in both Gr\"uneisen parameter and lattice thermal conductivity of ${\mathrm{Cu}}_{2}\mathrm{Ge}{\mathrm{Se}}_{3}$, and the underlying mechanism is thoroughly analyzed. With the fourth-order phonon scattering and temperature-induced renormalization, the calculated lattice thermal conductivities are well consistent with the experimental results. Due to the enhanced four-phonon scattering process, there are remarkable reductions for the thermal conductivity. In ${\mathrm{Cu}}_{2}\mathrm{Ge}{\mathrm{Se}}_{3}$, the coherences term ${\ensuremath{\kappa}}_{c}$ contributes increasingly to the total lattice thermal conductivity when temperature arises. And after considering the effects of temperature-induced renormalization and higher-order phonon-phonon interactions, the ${\ensuremath{\kappa}}_{c}$ would provide $\ensuremath{\sim}5%$ and above 25% of total conductivity at 300 and 800 K, respectively. Our finding clarifies the mechanism of low thermal conductivity in ${\mathrm{Cu}}_{2}\mathrm{Ge}{\mathrm{Se}}_{3}$, and benefits the design of similar Cu-based diamondlike materials in thermoelectric applications.

Thermal conductivity of Zr52.5Ti5Cu17.9Ni14.6Al10 alloy in as-cast glassy, relaxed and crystallized states

The thermal transport property of amorphous alloys is significant to understand the glass-forming ability and developing the thermal insulation coating. However, systematic studies on the thermal conductivity of alloys in as-cast glassy, relaxed and crystalline states are still scarce. Here, we systematically investigated the thermal conductivity behaviors in the temperature range of 10–300 K for as-cast glassy, relaxed, partially-crystallized and well-crystallized Zr52.5Ti5Cu17.9Ni14.6Al10 alloys. The total thermal conductivity (κ) of the as-cast Zr52.5Ti5Cu17.9Ni14.6Al10 metallic glass is approximately 5.66 Wm−1K−1 at room temperature and is slightly lower than that of the structurally relaxed sample, which can be attributed to the opposite changes in electronic thermal conductivity (κe) and phonon thermal conductivity (κp). In contrast, the total thermal conductivity of the partially-crystallized and well-crystallized Zr52.5Ti5Cu17.9Ni14.6Al10 alloys improves significantly owing to the abrupt decrease of electrical resistivity. In addition, the well-crystallized sample exhibits larger grains than the partially-crystallized sample, which will further enhance the phonon thermal conductivity. Our results lay a foundation for further understanding the mechanism of thermal conductivity evolution with the microstructure of metallic alloys.

Thermoelectric enhancement of p-type Si 80Ge 20 alloy via co-compositing of dual oxides: Respective regulation for power factor and thermal conductivity by β-Ga 2O 3 and SiO 2 aerogel powders

Si-based thermoelectric (TE) materials are exhibiting remarkable perspectives in self-energized applications with their special advantages. However, the relatively high total thermal conductivity (<i>κ</i>) prevents their TE enhancement. Here, a strategy of co-compositing dual oxides was implemented for enhancing the TE properties of p-type Si₈₀Ge₂₀ bulks. Composited Ga₂O₃ was demonstrated to enhance the power factor (<i>PF</i>) due to the crystallization-induced effect of produced Ga by decomposition on SiGe matrix. Associating with compositing SiO₂ aerogel (a-SiO₂) powder, not only introduced the fine amorphous inclusions and decreased the grain size of host matrix, but also various nano morphologies were formed, i.e., nano inclusions, precipitations, twin boundaries (TBs), and faults. Combining with the eutectic Ge, hierarchical scattering centers impeded the phonon transport comprehensively (decreasing the phonon group velocity (<inline-formula> <math display="inline" id="MA1"><mrow><msub><mi>v</mi><mtext>a</mtext></msub></mrow></math></inline-formula>) and relaxation time) for reducing the lattice-induced thermal conductivity (<inline-formula> <math display="inline" id="MA2"><mrow><msub><mi>κ</mi><mtext>l</mtext></msub><mo stretchy="false">)</mo></mrow></math></inline-formula>. As a result, a minimum <inline-formula> <math display="inline" id="MA3"><mi>κ</mi></math></inline-formula> of 2.38 W·m⁻¹·K⁻¹ was achieved, which is significantly dropped by 32.6% in contrast with that of the pristine counterpart. Ultimately, a maximal dimensionless figure of merit (<i>ZT</i>) of 0.9 was achieved at 600 ℃, which is better than those of most corresponding oxide-composited Si-based bulks.

Phonon Dominated Thermal Transport in Metallic Niobium Diselenide from First Principles Calculations.

Niobium diselenide (NbSe2) is a layered transition metal dichalcogenide material which possesses unique electrical and superconducting properties for future nanodevices. While the superconducting, electrical, and bulk thermal transport properties of NbSe2 have been widely studied, the in-plane thermal transport property of NbSe2, which is important for potential thermoelectric applications, has not been thoroughly investigated. In this report, we study the lattice in-plane thermal transport of 2D NbSe2 by solving the phonon Boltzmann transport equation with the help of the first principles calculation. The thermal conductivity obtained at room temperature is 12.3 W/mK. A detailed analysis shows that the transverse acoustic phonon dominates the lattice thermal transport, and an anomalously small portion of electron contribution to the total thermal conductivity is observed for this metallic phase. The results agree well with experimental measurements and provide detailed mode-by-mode thermal conductivity contribution from different phonon modes. This study can provide useful information for integrating NbSe2 in nanodevices where both electrical and thermal properties are critical, showing great potential for integrating monolayer NbSe2 to thermoelectric devices.

Engineering Multiple Microstructural Defects for Record-Breaking Thermoelectric Properties of Chalcopyrite Cu1- x Agx GaTe2.

Defect engineering for vacancies, holes, nano precipitates, dislocations, and strain are efficient means of suppressing lattice thermal conductivity. Multiple microstructural defects are successfully designed in Cu1- x Agx GaTe2 (0≤x≤ 0.5) solid solutions through high-ratio alloying and vibratory ball milling, to achieve ultra-low thermal conductivity and record-breaking thermoelectric performance. Extremely low total thermal conductivities of 1.28W m-1 K-1 at 300 K and 0.40Wm-1 K-1 at 873 K for the Cu0.5 Ag0.5 GaTe2 are observed, which are ≈79% and ≈58% lower than that of the CuGaTe2 matrix. Multiple phonon scattering mechanisms are collectively responsible for the reduction of thermal conductivity in this work. On one hand, large amounts of nano precipitates and dislocations are formed via vibrating ball milling followed by the low-temperature hot press, which can enhance phonon scattering. On the other hand, the difference in atomic sizes, distorted chemical bonds, elements fluctuation, and strained domains are caused by the high substitution ratio of Ag and also function as a center for the strong phonon scattering. As a result, the Cu0.7 Ag0.3 GaTe2 exhibits a record high ZTmax of ≈1.73 at 873K and ZTave of ≈0.69 between 300-873K, which are the highest values of CuGaTe2 -based thermoelectric materials.

Bismuth Telluride (Bi2Te3) nanocrystallites: Studies on growth morphology and its influence on the thermoelectric properties

Growth of Bismuth Telluride (Bi2Te3) nanocrystallites by solvothermal method resulted in an incomplete hexagonal flake-like (BTFL) structure for surfactant-free growth and complete hexagonal morphologies (BTHP) for the PVP surfactant mixed growth respectively identified through FESEM studies. XRD characterization revealed the crystallization of pure phase of Bi2Te3 at 210 °C for PVP-free growth and at 200 °C for PVP-assisted growth. Raman studies shows a noticeable difference in the appearance of peak positions for hexagonal nanoplatelets. Laser flash measurement of total thermal conductivity (κtot) resulted in the lowest value of 0.39 Wm−1K−1 for the BTFL pellet and 0.44 Wm−1K−1 for BTHP. Estimated lattice thermal conductivity resulted in 0.16 Wm−1K−1 for BTFL pellet and 0.25 Wm−1K−1 for the BTHP pellet. Temperature-dependent electrical conductivity studies reveal semiconductor behaviour for BTFL pellet and semi-metallic behaviour for BTHP pellet. Calculation of figure of merit (ZT) based on the measured values exhibits ZT value of 0.76 for BTFL and 0.64 for BTHP pellet. Details are presented in this paper.

Enhanced Thermoelectric Performance and Mechanical Property in Layered Chalcostibite CuSb1–xPbxSe2

In this work, the thermoelectric properties of p-type layered chalcostibite CuSb1–xPbxSe2 (x = 0–0.10) compounds prepared by vacuum melting reaction and uniaxial hot press, have been studied in the temperature range of 323–623 K. Further, aliovalent Pb2+ doping at Sb3+ site in CuSbSe2 notably increases the hole concentration due to its acceptor nature and thereby enhances the electrical conductivity, σ. Importantly, a huge reduction in total thermal conductivity, κtotal has been noticed, from ∼1.7 W/mK (pristine CuSbSe2) to ∼0.72 W/mK at 323 K for CuSb0.90Pb0.10Se2 owing to increased phonon scattering from the introduced point defects and mass-difference between Pb and Sb. As a result, the thermoelectric figure of merit, zT, has been enhanced to ∼0.27 at 623 K for the composition of CuSb0.90Pb0.10Se2, which is 3-fold higher than that of the undoped CuSbSe2. Further, the hardness value achieved was ∼125.54 Hv, which is significantly higher than the most of the state-of-the-art materials, indicating it to be an efficient thermoelectric material for intermediate temperature.

The influence of superplasticizers on the porous structure and thermal conductivity of lime foam concrete waste

the results of laboratory experiments are presented, where the use of lime waste (sludge) in foam concrete and the possibility of their use as a filler for foam concrete are analyzed. It is shown that the total porosity, thermal conductivity and structural quality of foam concrete with waste lime were taken as parameters of the porous structure.

Preparation and thermoelectric properties of Sc-doped Ti&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;NiSb half-Heusler alloys

The nominal composition TiNiSb with 19 valence electrons is demonstrated to be composed of off-stoichiometric half-Heusler phase and impurities. In this work, the Ti&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;NiSb (&lt;i&gt;x&lt;/i&gt; = 0, 0.10, 0.15, 0.20, 0.25) samples are prepared by ball milling and spark plasma sintering. The single-phase Ti&lt;sub&gt;0.9&lt;/sub&gt;NiSb sample, deviating from the theoretical composition Ti&lt;sub&gt;0.75&lt;/sub&gt;NiSb base on 18-electron rule, is obtained, which might be ascribed to the small defect formation energy of Ti filling the vacancy as well as our ball-milling preparation method. With the single-phase Ti&lt;sub&gt;0.9&lt;/sub&gt;NiSb sample used as the base material, a small amount of Sc is used to partially replace Ti in order to further reduce the carrier concentration. Thus, the Ti&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;–&lt;i&gt;y&lt;/i&gt;&lt;/sub&gt;Sc&lt;sub&gt;&lt;i&gt;y&lt;/i&gt;&lt;/sub&gt;NiSb (&lt;i&gt;x&lt;/i&gt; = 0.10, 0.15; &lt;i&gt;y&lt;/i&gt; = 0.03, 0.05) samples are designed to investigate the effect of Sc doping on the thermoelectric properties. The X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) analysis confirm the single-phase nature of the Ti&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;–&lt;i&gt;y&lt;/i&gt;&lt;/sub&gt;Sc&lt;sub&gt;&lt;i&gt;y&lt;/i&gt;&lt;/sub&gt;NiSb samples. Energy-dispersive X-ray spectroscopy (EDS) results indicate that the actual compositions of the Ti&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;–&lt;i&gt;y&lt;/i&gt;&lt;/sub&gt;Sc&lt;sub&gt;&lt;i&gt;y&lt;/i&gt;&lt;/sub&gt;NiSb samples are consistent well with their nominal compositions, and all elements are distributed uniformly in the sample. Moreover, the doping of Sc can increase the content of Ti vacancy while maintaining the single-phase structure, which could be attributed to the higher binding energy between Sc and Sb because the electronegativity of Sc is less than that of Ti. Both the substitution of Sc for Ti and the increase of the Ti vacancies significantly reduce the carrier concentration, which decreases from ~13.6 × 10&lt;sup&gt;21&lt;/sup&gt; cm&lt;sup&gt;–3&lt;/sup&gt; for Ti&lt;sub&gt;0.9&lt;/sub&gt;NiSb to ~3.4 × 10&lt;sup&gt;21&lt;/sup&gt; cm&lt;sup&gt;–3&lt;/sup&gt; for Ti&lt;sub&gt;0.8&lt;/sub&gt;Sc&lt;sub&gt;0.05&lt;/sub&gt;NiSb. The reduced carrier concentration results in greatly increased Seebeck coefficient, therefore the Ti&lt;sub&gt;0.8&lt;/sub&gt;Sc&lt;sub&gt;0.05&lt;/sub&gt;NiSb sample achieves a power factor as high as 17.7 μW·cm&lt;sup&gt;-1&lt;/sup&gt;·K&lt;sup&gt;-2&lt;/sup&gt; at 973 K. Although the lattice thermal conductivity of Sc-doped sample increases slightly due to the reduction of electron–phonon scattering and the enhancement of chemical bonds, the total thermal conductivity decreases dramatically due to the electronic thermal conductivity decreasing greatly. Finally, the Ti&lt;sub&gt;0.8&lt;/sub&gt;Sc&lt;sub&gt;0.05&lt;/sub&gt;NiSb sample reaches a &lt;i&gt;ZT&lt;/i&gt; value of ~0.42 at 973 K, which is 180% higher than that of Ti&lt;sub&gt;0.9&lt;/sub&gt;NiSb sample. Despite the fact that the thermoelectric performance of our sample is still inferior to those of the state-of-the-art off-stoichiometric 19-electron half-Heusler alloys, this work demonstrates that the thermoelectric performance of Ti&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;NiSb can be further improved by non-isoelectronic doping.

The problems of increasing the thermoelectric figure of merit of polycrystalline misfit layered compounds on (Gd-=SUB=-x-=/SUB=-Dy-=SUB=-1-x-=/SUB=-S)-=SUB=-z-=/SUB=-NbS-=SUB=-2-=/SUB=- example

The lattice disorder of different architecture and dimensions influence on the thermoelectric properties (Seebeck coefficient S, resistivity rho, total thermal conductivity kappatot,, power factor S2/rho, figure of merit ZT) of the polycrystalline ternary sulfides MTS3 was studied. The high-temperature misfit layered compounds (MS)zNbS2 (MS is GdxDy1-xS solid solutions) were chosen as objects of the study. The variation of gadolinium concentration along the series x=0.0, 0.1, 0.2, 0.5, 1.0 allowed one to alter the short-range and the long-range order of the crystal lattice and to study their effect on thermoelectric parameters of (GdxDy1-xS)zNbS2. At low concentration of x=0.1 the crystallite size increases, cause the deformation stresses decrease and, thereby, leads to an abnormal changes of S, rho, kappatot values and ZT decrease. An increase of the gadolinium concentration (x=0.2-0.5) alters the electronic structure and the interatomic bonding character of the incommensurate subsystems [GdxDy1-xS] and [NbS2]. In this case, S and rho values remains practically unaffected, while the thermal conductivity value decreases by 40% and ZT increases by 2 times. The nature of this phenomenon and the anisotropy of the thermoelectric properties were discussed. Keywords:: misfit layers compounds, thermoelectric properties, lattice disorder, solid solution, crystallite boundaries.

Проблемы увеличения термоэлектрической эффективности поликристаллической керамики несоразмерных слоистых соединений на примере (Gd-=SUB=-x-=/SUB=-Dy-=SUB=-1-x-=/SUB=-S)-=SUB=-z-=/SUB=-NbS-=SUB=-2-=/SUB=-

The lattice disorder of different architecture and dimensions influence on the thermoelectric properties (Seebeck coefficient S, resistivity , total thermal conductivity κtot, power factor S2/, figure of merit ZT) of the polycrystalline ternary sulfides MTS3 was studied. The high-temperature misfit layered compounds (MS)zNbS2 (MS is GdxDy1-xS solid solutions) were chosen as objects of the study. The variation of gadolinium concentration along the series x = 0.0, 0.1, 0.2, 0.5, 1.0 allowed one to alter the short-range and the long-range order of the crystal lattice and to study their effect on thermoelectric parameters of (GdxDy1-xS)zNbS2. At low concentration of x = 0.1 the crystallite size increases, cause the deformation stresses decrease and, thereby, leads to an abnormal changes of S, , κtot values and ZT decrease. An increase of the gadolinium concentration (x = 0.2–0.5) alters the electronic structure and the interatomic bonding character of the incommensurate subsystems (GdxDy1-xS) and NbS2. In this case, S and  values remains practically unaffected, while the thermal conductivity value decreases by 40% and ZT increases by 2 times. The nature of this phenomenon and the anisotropy of the thermoelectric properties were discussed.

Carrier-filtering and phonon-blocking AgSnSe2-decorated grain boundaries to boost the thermoelectric performance of Cu2Sn0.9Co0.1S3.

Heavily co-doped Cu2SnS3 can achieve a high power factor by relying on a high electrical conductivity (σ), which subsequently limits the ZT value with a large electronic thermal conductivity (κe). We report here an enhanced ZT for Cu2Sn0.9Co0.1S3 decorated with micro-nanoscale AgSnSe2 along grain boundaries. The AgSnSe2 phase served as a charge carrier filter by ionized impurity scattering, with a noticeable bottoming out of carrier mobility and a rapid increase in the Seebeck coefficient as the temperature increased from 423 to 573 K, which properly reduced the large σ and κe while maintaining a high power factor of approximately 10 μW cm-1 K-2 at 773 K. Lattice thermal conductivity was markedly suppressed, and a low total thermal conductivity was obtained with strengthened phonon scattering by the AgSnSe2 phase as a phonon barrier. With the synergistic effects on electrical and thermal transport, a maximum ZT of 0.93 at 773 K was achieved in Cu2Sn0.9Co0.1S3-3 wt% AgSnSe2.

Enhancement of low-temperature thermoelectric performance via Pb doping in Cu3SbSe4

We investigated the synthesis protocols of the pure and Pb-doped bulk polycrystalline Cu3Sb1-xPbxSe4 (0 ≤ x ≤ 0.04) system and studied their crystallographic and thermoelectric properties intending to reach a high figure of merit (ZT). The solid-state reaction method under a 10−5 Torr vacuum was employed to synthesize the pristine and doped samples. The Rietveld analysis of room-temperature X-ray diffraction confirmed tetragonal structure with space group I4‾2m for all studied compositions. The electrical resistivity [ρ(T)] demonstrated a degenerate semiconducting behavior for pure as well as doped samples. The overall ρ(T) increased with increasing Pb content. The positive values of Seebeck coefficient [S(T)] data in the investigated temperature range for all the studied compositions revealed that holes played a major role in the conduction mechanism. The S(T) values rose with increased temperature, a characteristic of degenerate semiconductors. The temperature-dependent Seebeck coefficient data analysis revealed a narrow bandgap behavior for all studied samples. The analysis suggests that the electronic thermal conductivity only contributed up to 1% to the total thermal conductivity, and the remaining 99% was contributed by lattice thermal conductivity. The estimated ZT values showed as much as 20% enhancement at 380 K for a 1% doped sample, Cu3Sb0.99Pb0.01Se4. The thermoelectric compatibility factor decreased with doping, and a maximum value (1.14 V−1) was found for the pristine sample at 250 K.