Cr2TiAlC2 MAX phase was synthesized for the first time by reactive spark plasma sintering (SPS) from pure metallic precursors. A systematic study of each SPS parameter was performed to promote the formation of the pure phase. The transport properties of the resulting pellet were probed and compared to a conventionally synthesized sample made from pure Cr2TiAlC2 densified powder. The electrical conductivity was measured to be 8.31 × 105 S.m-1 at 298 K, while the thermal conductivity was measured to be 11.76 W.m-1.K-1 at 298 K, one of the lowest values reported for a MAX phase. The measured Vickers hardness was 7.62 ± 0.16 GPa at a load of 19.8 N, which is about 40% higher than samples synthesized by hot pressing, making it the hardest 312 MAX phase reported to date. Although Cr2TiAlC2 was confirmed to be a poor thermoelectric compound, exhibiting a low Seebeck coefficient of -4.2 μV.K-1 at 298 K. These results provide a baseline for comparing structural and transport properties prior to etching into MXenes, thereby helping to better understand the influence of dimensional reduction on thermoelectric performance. Overall, these results demonstrate that reactive SPS is a rapid and efficient method for MAX phase synthesis.

We report a rare-earth-free multi-filling strategy to enhance the thermoelectric performance of Co4Sb12 skutterudites. Co-filling with In and Ga, along with partial Sb for Te substitution induces beneficial compositing effect, refines grain size, and tunes filler's solubility. An optimal In:Ga ratio, achieved in In0.3Ga0.1Co4Sb11.8Te0.2, maximizes dodecahedral site occupancy and yields a high power factor (approximate to 40 mu Wcm-1 K-2) in the 300-600 K range, reaching values close to that of rare-earth-filled skutterudites.

Unfilled Co4Sb12 skutterudites typically exhibit n-type conductivity at room temperature due to native donor-type defects associated with off-stoichiometric compositions arising from Sb loss during high-temperature synthesis. Achieving stable p-type conductivity in the absence of rare-earth fillers or transition-metal substitution at the Co site remains a significant challenge. Here, we report an in situ composite engineering approach in which elemental Bi (x = 0, 3, 6, 11 wt.

Synergizing high performance and long-term stability in thermoelectric materials remains a formidable challenge, particularly for eco-friendly Cu-S compounds, which have outstanding performance but are plagued by thermal degradation at elevated temperatures and copper ion migration under electric fields. Herein, a promising in-situ heterostructure (Cu2-xS-CuInS2) strategy induced by isoatomic In substitution in Cu1.93S was demonstrated to unlock the threefold balance among thermoelectric performance, thermal stability, and electrical stability. This strategy tunes the Cu vacancy content in the primary Cu2-xS phase and the fraction of the secondary CuInS2 phase, thereby suppressing carrier scattering while preserving ultralow lattice thermal conductivity and a high power factor. The optimized Cu1.89In0.04S achieves a peak zT of 1.57 at 873 K and an average zT of 1.31 over 723-873 K, ranking among the highest values within binary Cu-S thermoelectrics. Crucially, the heterostructure strategy imparts exceptional durability, as evidenced by negligible degradation under thermal cycling and remarkable resistance to current-induced failure, wherein ionic hysteresis at heterointerfaces suppresses Cu migration. Overall, these results underscore heterostructure engineering as a compelling route to transcend the intrinsic limitations of Cu-S compounds, charting a pathway toward next-generation of thermoelectric materials that couple high performance with long-term reliability. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

It has been proved that digenite (Cu1.8S) is an electrically stable material under high current stress testing which is an attractive feature within the binary Cu-S system. However, the underlying thermal stability in the middle temperature region (673-773K) has been under-investigated. Focusing on the method of synthesis could be an effective way to optimize the thermal stability and also thermoelectric performance. Herein, three synthesis methods including Solid State (SS), Mechanical Alloying (MA), and Hot Injection (HI) combined with Spark Plasma Sintering (SPS) were investigated. Pure Cu1.8S was obtained from each synthesis method and the resulting samples showed distinguishable microstructures. Benefiting from the relatively low thermal conductivity, the highest zT of 0.44 at 773 K is obtained by the MA method. Moreover, we demonstrate that the underlying thermal instability of Cu1.8S prepared by the three methods show significant differences. MA promotes the highest chemical thermal stability up to 773 K compared to the SS sample (approximate to 723 K) and HI sample (approximate to 425 K) via thermogravimetric/dynamic scanning calorimetry (TG/DSC). A mismatch between the structural stability, determined by high-temperature X-ray diffraction (HT-XRD), and the chemical stability was attributed to the offstoichiometry range existing in this Cu2-xS system at high temperatures. Thermal diffusivity cycling testing showed that MA yielded the most stable sample under N2 flux compared to SS. However, under a partial He atmosphere, the sulfur evaporation is accelerated, indicated from variation in the thermoelectric properties of SS and MA samples. This study illustrates the importance in selecting the appropriate synthesis method for sulfide- based materials to process stable and optimized TE ceramics, as well as showing that the influence of the measuring condition to the cycling stability of thermoelectric property is crucial. Finally, we suggest that use of the MA method in conjunction with SPS is optimum to produce the most stable digenite samples.

The Cu-S superionic compound exhibits excellent thermoelectric (TE) performance in the mid-temperature region. However, obtaining a thermally and electrically stable material in this system is still challenging. Herein, motivated by the perspective of steric confinement for suppressing Cu+ migration, we designed an Ag and Ag-Se co-doping strategy on pristine Cu1.93S to modulate the crystal structure. On one hand, Ag dopant is discovered to act as a vacancy filler, simultaneously optimizing carrier concentration and reducing thermal conductivity. Moreover, strategic Se co-substitution stabilizes Ag insertion within the Cu-S vacancy and induces non-negligible enhancement of phonon scattering to further reduce thermal conductivity. A competitive peak zT of 1.33@873 K was obtained for the Cu1.93Ag0.04S0.9Se0.1 sample at a relatively moderate temperature among current state-of-the-art Cu-S system. Moreover, thanks to the steric confinement, the Cu1.93Ag0.04S0.9Se0.1 composition exhibited superior electrical stability under dynamic DC-current compared to CuxS (with 1.93

Yttrium and rare-earth iron garnets (R3Fe5O12) are ferrimagnetic insulators that have been widely studied for magnetic and spintronic applications. In this study, we report the thermal conductivity (κ) between 300 and 773 K for the single crystals ofR3Fe5O12, whereR= Y, Gd, Dy, and Yb. For Y3Fe5O12, theκup to the Curie temperature (TC≈ 555 K) can be described well with a pure phononic model, without considering conduction or scattering by the magnons. The iron garnets containing magnetic rare-earth ions exhibit smallerκ, with Dy3Fe5O12showing the smallest values due to the strong interactions of heat-carrying phonons with the crystal field excitations of Dy3+ions.

In the present study, for the first time, aluminum-doped zinc oxide (AZO) thin films with nanoinclusions of amorphous carbon have been synthesized via spin coating, and the thermoelectric performances were investigated varying the aging period of the solution, the procedure of carbon nanoparticles’ addition, and the annealing atmosphere. The addition of nanoparticles has been pursued to introduce phonon scattering centers to reduce thermal conductivity. All the samples showed a strong orientation along the [002] crystallographic direction, even though the substrate is amorphous silica, with an intensity of the diffraction peaks reaching its maximum in samples annealed in the presence of hydrogen, and generally decreasing by the addition of carbon nanoparticles. Absolute values of the Seebeck coefficient improve when nanoparticles are added. At the same time, electric conductivity is higher for the sample with 1 wt.% of carbon and annealed in Ar with 1% of H2, both increasing in absolute value with the temperature rise. Among all the samples, the lowest thermal conductivity value of 1.25 W/(m∙K) was found at room temperature, and the highest power factor was 111 μW/(m∙K2) at 325 °C. Thus, the introduction of carbon effectively reduced thermal conductivity, while also increasing the power factor, giving promising results for the further development of AZO-based materials for thermoelectric applications.

Decoupling charge and heat transport is essential for optimizing thermoelectric materials. Strategies to inhibit lattice-driven heat transport, however, also compromise carrier mobility, limiting the performance of most thermoelectrics, including Fe 2 VAl Heusler compounds. Here, we demonstrate an innovative approach, which bypasses this tradeoff: via liquid-phase sintering, we incorporate the archetypal topological insulator Bi 1− x Sb x between Fe 2 V 0.95 Ta 0.1 Al 0.95 grains. Structural investigations alongside extensive thermoelectric and magneto-transport measurements reveal distinct modifications in the microstructure, a reduced lattice thermal conductivity and a simultaneously enhanced carrier mobility arising from topologically protected charge transport along the grain boundaries. This yields a huge performance boost, resulting in one of the highest figure of merits among both half- and full-Heusler compounds, z ≈ 1.6 × 10 −3 K −1 ( z T ≈ 0.5) at 295 K. Our findings highlight the potential of topological-insulating secondary phases to decouple charge and heat transport and call for more advanced theoretical studies of multiphase composites.

Multinary sulfides represent a significant family of semiconductors because of their low cost and promising performance, yet controlling their composition is challenging. CuFeS2 thin films are particularly attractive because of their great potential in thermoelectricity and photovoltaics. Herein we reveal the newest finding that Zn promotes the cation ordering and stabilizes the chalcopyrite CuFeS2 film, preventing the reverse transformation to wurtzite with a random distribution of Cu-Fe at high temperature. The thermoelectric properties of chalcopyrite thin films are investigated as a function of Zn content, resulting in an optimized power factor of 0.168 mW/mK2 at room temperature, outperforming any CuFeS2 thin films ever reported. For the first time, synchrotron-based in situ X-ray diffraction and X-ray absorption fine structure confirm the phase transition, offering insights into the isomeric structure of CuFeS2 and the role of Zn. The in-depth understanding of cation-ordering and phase transformation between CuFeS2 polymorphs might impact the multinary sulfide film fabrication and improvement in efficiency of renewable energy applications.

Pristine GeTe is an archetypal mid-temperature thermoelectric, but its full potential is obscured by an eleven-dimensional process space. We combine active learning with Bayesian optimisation (ALBO) to traverse this landscape, encompassing melt-annealing and spark-plasma-sintering conditions. Starting from five random experiments, ALBO iteratively proposes batches of five new recipes by maximising the expected improvement in the figure-of-merit $zT$zT; each batch is synthesised, characterised, and used to retrain the surrogate. After only 24 experiments - four orders of magnitude fewer than an exhaustive search - we raise the 700 K $zT$zT of undoped GeTe from 0.86 to 1.14, a 25% gain over the best conventional two-step route and comparable to multi-day three-step protocols. Post-hoc analysis reveals that melt-cooling rate and SPS dwell/cooling profiles dominate performance by controlling the Ge-vacancy population and microstructure. ALBO therefore provides a time- and energy-efficient path to process optimisation while simultaneously exposing the key levers that govern transport in GeTe, and the strategy is readily transferable to other materials where processing, rather than chemistry, limits performance.

As a crucial parameter in the determination of thermal conductivity, the heat capacity of Cu2+xZn1-xSnS4 (CZTS) has been investigated and analyzed in detail from 2 to 773 K. The effects of the Cu-Zn stoichiometric ratio and phase transition have been quantified and correlated with entropy variation. We confirm that the compounds follow the Dulong-Petit approximation above the Debye temperature theta D and solve literature discrepancies on CZTS. The in-depth low-temperature heat capacity analysis revealed an approximate image of the energy dependence of the phonon density of state in kesterite, which agrees with the results of first-principles calculations. The importance of the heat capacity measurement is reported to estimate and analyse accurately the structural and thermal transport behaviour in kesterite-Cu2ZnSnS4.

Forming lateral heterojunctions in two-dimensional materials enables taking full advantage of their attractive properties. In their Communication (e202318181), Hiroshi Nishihara et al. report a novel method to fabricate a lateral heterojunction exhibiting rectifying properties by sequentially immersing a coordination nanosheet synthesized from zinc ions and benzenehexathiol into iron and copper salt solutions.

Decoupling charge and heat transport is essential for optimizing thermoelectric materials. Strategies to inhibit lattice-driven heat transport, however, also compromise carrier mobility, limiting the performance of most thermoelectrics, including Fe2VAl Heusler compounds. Here, we demonstrate an innovative approach, which bypasses this tradeoff: via liquid-phase sintering, we incorporate the archetypal topological insulator Bi1-xSbx between Fe2V0.95Ta0.1Al0.95 grains. Structural investigations alongside extensive thermoelectric and magneto-transport measurements reveal distinct modifications in the microstructure, a reduced lattice thermal conductivity and a simultaneously enhanced carrier mobility arising from topologically protected charge transport along the grain boundaries. This yields a huge performance boost - far beyond the effective-medium limit - and results in one of the highest figure of merits among both half- and full-Heusler compounds, z ≈ 1.6 x 10^-3 K^-1 (zT ≈ 0.5) at 295 K. Our findings highlight the potential of topological-insulating secondary phases to decouple charge and heat transport and call for more advanced theoretical studies of multiphase composites.

AbstractHeterostructures of two‐dimensional materials realise novel and enhanced physical phenomena, making them attractive research targets. Compared to inorganic materials, coordination nanosheets have virtually infinite combinations, leading to tunability of physical properties and are promising candidates for heterostructure fabrication. Although stacking of coordination materials into vertical heterostructures is widely reported, reports of lateral coordination material heterostructures are few. Here we show the successful fabrication of a seamless lateral heterojunction showing diode behaviour, by sequential and spatially limited immersion of a new metalladithiolene coordination nanosheet, Zn3BHT, into aqueous Cu(II) and Fe(II) solutions. Upon immersion, the Zn centres in insulating Zn3BHT are replaced by Cu or Fe ions, resulting in conductivity. The transmetallation is spatially confined, occurring only within the immersed area. We anticipate that our results will be a starting point towards exploring transmetallation of various two‐dimensional materials to produce lateral heterojunctions, by providing a new and facile synthetic route.

Outdoor radiative cooling is a passive method of cooling a surface that faces the sky. During the past decade, numbers of successful demonstrations of daytime radiative coolers have been reported. Because a daytime radiative cooler can be radiatively cooled both during the day and at night, it is always cooled and a temperature difference against the surroundings is generated. This temperature difference can be used to generate thermoelectric power throughout the day by placing a daytime radiative cooler on a thermoelectric module. However, such a device cannot harvest solar heat because sunlight is reflected by the daytime radiative cooler. In this study, a thermoelectric device that simultaneously harvests both radiative cooling and solar heating is presented. The essential component is a vertically placed thermoelectric module made of transparent thermoelectric thin films which allows radiatively cooled and solar heated surfaces to be co-planar. The outdoor and indoor measurements confirm that the device can harvest both radiative cooling and solar heating simultaneously during the day without offsetting each other, and can harvest radiative cooling at night. The co-planar design is an efficient method for simultaneously harvesting solar heating and radiative cooling, which could facilitate efficient energy harvesting and can be applied to a standalone power supply for off-grid sensor modules.

The novel quaternary compound Rb0.2Ba0.4Cr5Se8 was synthesized and characterized in both single crystal and polycrystalline forms. Crystallizing in the monoclinic crystal system (space group C2/m, cell parameters a = 18.7071(4) & Aring;, b = 3.6030(1) & Aring;, c = 8.9637(3) & Aring;, beta = 104.494(2)degrees) and isostructural to pseudo-hollandite compounds, it features mixed Rb and Ba occupancy within its one-dimensional channels. High-temperature X-ray diffraction revealed no decomposition up to 973 K, and the thermal expansion coefficient at 300 K was determined to be 2.6(1)10(-5) K-1. Spin-polarized density functional theory (DFT) calculations showed that the density of states for Rb0.2Ba0.4Cr5Se8 is more polarized than that of Ba0.5Cr5Se8, resulting in a higher Seebeck coefficient, which was experimentally confirmed to reach a peak value of 400 mu VK-1 at 620 K. Resistivity measurements indicated a degenerate semiconducting behavior below 550 K, with a resistivity peak of 100 m Omegacm at that temperature, leading to a maximum power factor of 0.21 mWm(-1)K-2. Thermal conductivity measurements indicated low values around 0.8 Wm(-1)K-1 in the 300-900 K range, resulting in a thermoelectric figure of merit of 0.22 at 873 K. Decorrelated transport properties observed in this double-inserted pseudo-hollandite compound make Rb0.2Ba0.4Cr5Se8 a good example of beneficial synergistic effects for higher thermoelectric performance.

BaZrO3 and KTaO3 are two rare examples of perovskite oxides that retain the ideal cubic structure down to the lowest temperature. In this paper, we report thermal conductivity (kappa) between 300 and 773 K on single crystals of these compounds. For BaZrO3, the kappa of 7.5 Wm(-1)K(-1) at 300 K is similar to 40% larger than the previously reported polycrystalline values. For KTaO3, our value of 13.1 Wm(-1)K(-1) at 300 K clarifies the sources of error in some of the previously reported data. These results underscore the importance of high-quality experimental data in benchmarking the accuracy of advanced first-principles kappa calculations.

The thermal process parameters are crucial in metal-sulfides ceramics as they affect significantly the resulting physico-chemical properties. In the present work, we investigated the sintering effect in the kesterite Cu2.125Zn0.875SnS4 on its structural, microstructural, and thermoelectric (TE) properties to highlight the non-negligible contribution of the thermal process often ignored in metal-sulfide ceramics. For this purpose, we developed an approach combining data science with the conventional material experiment/theory approach which can be used as a tool to shortcut the time-consuming steps of TE material optimization. We confirmed that the optimization and control of the densification process is critical in unravelling the highest potential on metal sulfide TE ceramics with a non-negligible increase of its zT up to 60%. We propose a scientific tool, the synergic combination of active machine learning with conventional chemistry/theory approaches, to either identify the most proficient sintering process as well as the process to avoid the degradation of the metal-sulfide ceramic properties and thus in a shorten number of experiments. This approach can be extended not only to other metal-sulfide ceramics for thermoelectricity but also to other research fields.

Decoupling charge and heat transport is essential for optimizing thermoelectric materials. Strategies to inhibit lattice-driven heat transport, however, also compromise carrier mobility, limiting the performance of most thermoelectrics, including Fe_2VAl Heusler compounds. Here, we demonstrate an innovative approach, which bypasses this tradeoff: via liquid-phase sintering, we incorporate the archetypal topological insulator Bi_1-xSb_x between Fe_2V_0.95Ta_0.1Al_0.95 grains. Structural investigations alongside extensive thermoelectric and magneto-transport measurements reveal distinct modifications in the microstructure, and a reduced lattice thermal conductivity and enhanced carrier mobility are simultaneously found. This yields a huge performance boost - far beyond the effective-medium limit - and results in one of the highest figure of merits among both half- and full-Heusler compounds, z≈ 1.6× 10^-3K^-1 (zT≈ 0.5) at 295 K. Our findings highlight the potential of secondary phases to decouple charge and heat transport and call for more advanced theoretical studies of multiphase composites.