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Recently, rock-salt lead-free chalcogenide SnTe-based thermoelectric (TE) materials have been considered an alternative to PbTe because of the nontoxic properties of Sn as compared to Pb. However, high carrier concentration that originated from intrinsic Sn vacancies and relatively high thermal conductivity of pristine SnTe lead to poor TE efficiency, which makes room for improving its TE properties. In this study, we present that the Na incorporation into the SnTe matrix is helpful for modifying the electronic band structure, optimization of carrier concentration, introducing dislocations, and kink planes; benefiting from these synergistic effects obviates the disadvantages of SnTe and makes a significant improvement in TE performance. We reveal that Na favorably impacts the structure of electronic bands by valence, conduction band engineering, leading to a nice enhancement in the Seebeck coefficient, which exhibits the highest power factor value of 37.93 μWcm

A flexible n-type Ag2Se thin film with a high power factor (PF) of 21.6 μW cm−1 K−2 and a ZT value over 0.6 was successfully prepared by a facile self-assembled growth method.

Owing to the unique features, such as mechanically robust, low-toxic, high stability, and high thermoelectric performance, CoSb3-based skutterudite materials are among art-of-the state thermoelectric candidates. In this work, we develop a facile in-situ method for the growth of well-crystallinity (Ag, Sn) co-doped CoSb3 thin films. This preparation method can efficiently control the dopant concentration and distribution in the thin films. Both the density functional theory calculation and the experimental results suggest that Sn and Ag dopants trend to enter the lattice and preferentially fill interstitial sites. Additionally, band structure calculation results suggest that the Fermi level moves into the conduction bands due to co-doping and eventually induces the increased electrical conductivity, which agrees with the optimization of carrier concentration. Moreover, an increase in the density of state after co-doping is responsible for the increased Seebeck coefficient. As a result, the power factors of (Ag, Sn) co-doped CoSb3 thin films are greatly enhanced, and the maximum power factor achieves over 0.3 mW m−1 K−2 at 623 K, which is almost two times than that of the un-doped CoSb3 film. Multiple microstructures, including Sb vacancies and Ag/Sn interstitial atoms as point defects, and a high density of lattice distortions coupled with nano-sized Ag-rich grains, lead to all scale phonon scatterings. As a result, a reduced thermal conductivity of ∼0.28 W m−1 K−1 and a maximum ZT of ∼0.52 at 623 K are obtained from (Ag, Sn) co-doped CoSb3 thin films. This study indicates our facile in-situ growth can be used to develop high-performance dual doped CoSb3 thins.

Te-free n-type Bi2O2Se is one of the promising thermoelectric materials due to its high chemical stability and eco-friendliness. However, its conversion efficiency reported so far is still low. Hen...

In this work, we investigated the effects of annealing process on thermoelectric performance for Pb0.06Bi0.94Cu0.94SeO sample. Under the appropriate annealing time of 573 K, the electrical conductivity was significantly improved on the premises of a higher carrier concentration. As a result, a high power factor of 1096 µWm−1 K−2 was achieved at 323 K. Furthermore, the lattice thermal conductivity obviously decreased as the annealing time rose up to 3 days, which mostly benefited from the stronger phonon scattering and the precipitation of the second phase. Consequently, for the Pb0.06Bi0.94Cu0.94SeO sample annealed for 1 day, a maximum ZT value of 0.85 was obtained at 873 K, which was 57% and 12% higher than those of pristine BiCuSeO and un-annealed sample, respectively. This work proposes an effective post-treatment strategy to enhance the thermoelectric properties of BiCuSeO-based compounds.

To obtain p-type Bi–Sb–Te-based thin films with excellent thermoelectric performance, the Bi0.4Sb1.6Te3 target is prepared by combining mechanical alloying with the spark plasma sintering technique. Afterward, Bi0.4Sb1.6Te3 thin films are deposited via magnetron sputtering at variable working pressures. With an increasing working pressure, the frequency of collisions between the argon ions and sputtered atoms gradually increases, the preferred orientation of (00l) increases, and the sputtering rate decreases. The Seebeck coefficient increases from ∼140 μV/K to ∼220 μV/K as the carrier concentration decreases along with an increasing working pressure. Furthermore, the decrease in carrier concentration and acceleration of carrier mobility also affect the change in electrical conductivity. The maximum power factor of the p-type Bi0.4Sb1.6Te3 thin film deposited at 4.0 Pa and at room temperature exceeds 20.0 μW/cm K2 and is higher than that of most p-type Bi–Sb–Te-based films.

Zinc antimonide (Zn–Sb) is considered as a good candidate to replace the traditional TE materials due to its low cost, non-toxic, and high abundance of elements. In this work, layer-by-layer thin films were fabricated by sputtering Zn on the Sb precursor layer with a magnetron sputtering method, and an annealing process is performed on thin films to engage a self-assembled growth of Zn–Sb films. It is found that Zn–Sb film with good crystallinity was obtained after annealing at 300 ℃ for 10 min. Then, the influence of Zn layer thickness and annealing time on the structural, compositional, and thermoelectric properties for the Zn–Sb thin films were investigated. As a result, the thin film with mixed Zn4Sb3/ZnSb phases achieved a high power factor of 3.42 µWcm−1 K−2 when the Zn layer thickness was 600 nm. Additionally, the power factor was further optimized to 3.80 µWcm−1 K−2 after prolonging the annealing time up to 15 min.

In this work, n-type Bi2Te3 based thin films were prepared in 300 °C via DC magnetron sputtering, and influences of sputtering power and annealing time on thermoelectric properties of films were investigated. The raise of sputtering power brings about the improvement of deposited rate and enhancement of grain size. Taking the consideration that the large-sized grains are to phonon scattering, we determine the medial power of 30 W as the basic technical parameters for the purpose of further optimizing performance through an in situ annealing process. Subsequently, thin-film treated by in situ annealing process acts out an obvious reduction in electrical conductivity attributed to the decrease in carrier concentration. Especially, the film annealed for 40 min shows an enhancement in the Seebeck coefficient and leads to a maximum power factor 0.82 m W m−1 K−2 at 543 K.

International audience; Searching for eco-friendly and earth-abundant materials to supersede traditional high-cost bismuth telluride for fabricating wearable devices is of great significance in thermoelectrics. In this work, promising flexible Cu2Se based thin films with high thermoelectric performance is successfully fabricated via a facile co-sputtering method. Experimental results indicate that excess Cu in Cu2Se films leads to the decrease of carrier concentration by suppressing the formation of Cu vacancies and donating electrons, benefiting to achieve high Seebeck coefficient. Moreover, Cu-excess Cu2Se films have highly (0l0) preferred orientation and extra high carrier mobility, maintaining the decent electrical conductivity in the whole measurement temperature range. Combined with the low thermal conductivity, a maximum ZT of 0.42 is obtained at 275 °C from the Cu-excess Cu2Se due to the simultaneous optimization both of electrical and heat transport. Subsequently, a flexible thermoelectric device assembled with high performance Cu2Se films exhibits a maximum power density of 4.28 Wm-2 at a temperature difference of 50 °C, which thermal stability is greatly improved after introducing a molybdenum buffer layer into electrode layer. Therefore, this work demonstrates that rational microstructure manipulations and connection technology improvement can achieve high performance in the flexible thermoelectric device, which possess potential in wearable applications.

Flexible Bi

This work reports on the thermoelectric properties of bulk SnS2, which shows a similar composition and layered crystal structure to the extensively studied SnS and SnSe. The synthesis process for mechanical alloying (MA) SnS2 was also investigated. The SnS2 compound was formed in the reaction between SnS and S, after the formation of SnS using Sn and S as raw materials. However, single-phase SnS2 appears to be difficult to obtain by MA because Sn2S3 is produced when milling times are extended. Nevertheless, a pure-phase SnS2 bulk is achieved by further spark plasma sintering. The pristine SnS2 bulk shows an n-type conductive characteristic and a moderate absolute Seebeck coefficient between 100 and 700 μV/K. However, with a low figure of merit value ZT, the thermoelectric property is poor because of the low electrical conductivity of below 0.2 S/cm and the relatively high thermal conductivity of above 1.5 W/mK. Further, the electrical conductivity is enhanced and the thermal conductivity decreases significantly after Ag doping. An enhanced ZT value of 0.01 is achieved which is two times higher than pristine one.

The influence of Pb/Ag dual doping on the thermoelectric performance of BiCuSeO was investigated. It reveals that the electrical conductivity can be obviously improved owing to the increased carrier concentration mostly caused by the divalent Pb2+ doping at trivalent Bi3+. The electrical conductivity improves from 7.29 S/cm for BiCuSeO to 397.40 S/cm for Pb0.06Bi0.94Cu0.94Ag0.06SeO and Pb0.06Bi0.94CuSeO at 327 K. Combined with the moderate Seebeck coefficient (>120 μV/K) due to the large effective mass, a large power factor with 834 μW/mK2 is achieved. Meanwhile, the lattice thermal conductivity is visibly decreased, mainly benefiting from the substitution of Ag+ at the Cu+ site since the phonon scattering can be enhanced by mass fluctuation and strain fluctuation between the two elements. Thus, the total thermal conductivity is suppressed effectively compared with the Ag-free sample Pb0.06Bi0.94CuSeO. Finally, a maximum ZT value with nearly 1.0 has been obtained for Pb0.06Bi0.94Cu0.94Ag0.06SeO at 873 K, which is ∼64% and ∼47% larger than those of the pristine sample BiCuSeO and Ag-free sample Pb0.06Bi0.94CuSeO. Additionally, the ZT is also larger than the maximum value for the reported Pb-free samples BiCu0.94Ag0.06SeO and Bi0.92Ag0.08CuSeO, suggesting Pb and Ag are effective codopants of BiCuSeO to synergetically tune its electrical and thermal transport properties.

Photocatalytic technology has got great attention in recent days because of increasing problems of energy crisis and environmental pollution. Many semiconductor photocatalyst has been investigated, among them BiFeO3 has got great attention due to its unique morphological structural and multiferroic properties. In this review, detailed discussion of crystal structure, electronic band structure, degradation mechanism, different factors affecting on degradation efficiencies of BiFeO3 has been included. The different fabrication techniques and possibilities of improvement photoactivity of BiFeO3 with different modification were also discussed. This review also gives a broad overview of BiFeO3 as visible light photocatalysts, summarizing the present state of research work and providing some useful understandings for their future progress. Keywords: BiFeO3, Visible-light, Photocatalysis, Nanostructures

A series traditional thermoelectric films, including n-type Bi, Bi2Te3, and p-type Sb, Sb2Te3, were synthesized with CH3NH3I by combining magnetron sputtering and thermal evaporation method. It is found that the Seebeck coefficients for all the composite films have enhanced although the electrical conductivities reduced due to the decreased carrier concentration. This leads to an obvious improvement of the power factor, especially for p-type Sb2Te3-based organic–inorganic hybrid films. As expected, a maximum power factor value around 2.3 mWm−1K−2 has been achieved for the composition of Sb2Te3/CH3NH3I in range of the whole measured temperature, which is nearly seven times higher than that of pristine Sb2Te3 film. By combination with the reduced thermal conductivity, a ZT value nearly 1.0 has been obtained at 380 K for the composition of Sb2Te3/CH3NH3I.

Poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate)/carbon nanotube (PEDOT:PSS/CNTs) composite films have been demonstrated to offer an excellent thermoelectric performance. In this work, p-type thermoelectric films prepared by a simple dipping coating process based on the carbon-coated carbon nanotubes (C-CNTs) continuous network are investigated. The highest power factor obtained in this work is 504.8 μW/mK2 (at 300 K) due to the relatively high electrical conductivity and Seebeck coefficient. The excellent TE properties of the C-CNTs/PEDOT:PSS composite film are attributed to the interfacial carrier scattering introduced by the unique structure. Composite materials based on a continuous network would open up new opportunities to develop high performance organic thermoelectric materials.

International audience; Inorganic films possess much higher thermoelectric performance than their organic counterparts, but their poor flexibilities limit their practical applications. Here, Sb2Te3/Te-x hybrid thin films with high thermoelectric performance and flexibility, fabricated via a novel directional thermal diffusion reaction growth method are reported. The directional thermal diffusion enables rationally tuning the Te content in Sb2Te3, which optimizes the carrier density and leads to a significantly enhanced power factor of >20 mu W cm(-1) K-2, confirmed by both first-principles calculations and experiments; while dense boundaries between Te and Sb2Te3 nanophases, contribute to the low thermal conductivity of approximate to 0.86 W m(-1) K-1, both induce a high ZT of approximate to 1 in (Sb2Te3)(Te)(1.5) at 453 K, ranking as the top value among the reported flexible films. Besides, thin films also exhibit extraordinary flexibility. A rationally designed flexible device composed of (Sb2Te3)(Te)(1.5) thin films as p-type legs and Bi2Te3 thin films as n-type legs shows a high power density of >280 mu W cm(-2) at a temperature difference of 20 K, indicating a great potential for sustainably charging low-power electronics.

International audience; Owing to the earth-abundancy, eco-friendliness and high thermoelectric performance, CoSb3 skutterudites have been employed in thermoelectric devices with a high energy conversion efficiency. However, the thermoelectric performance of CoSb3-based thin films is still relatively low within the medium temperature range. In this work, we report a record high ZT of ~0.65 at 623 K in the n-type Ag/In co-doped CoSb3 thin films, fabricated by a facile magnetron sputtering technique. Extensive characterizations and computational results indicate both Ag and In as fillers prefer to occupy the interstitial sites in the CoSb3 lattice. A 0.2% Ag doping induces impurity states in the band structure of CoSb3, boosts the density-of-states near the Fermi level and enhances the absolute Seebeck coefficient up to ~198 μV K−1. Simultaneously, a 4.2% In doping further tunes the bandgap, increases the electrical conductivity up to ~75 S cm−1, and contributes to an optimized power factor of ~2.94 μW cm−1 K−2 at 623 K. In addition, these interstitial dopants accompanying with dense grain boundaries contribute an ultra-low thermal conductivity of ~0.28 W m−1 K−1 at 623 K, leading to a high ZT in the film system. This work demonstrates that rational band engineering and structural manipulations can achieve high performance in n-type CoSb3-based thin films, which possess full potential for applying to miniature thermoelectric devices.

International audience; Copper selenide (Cu2Se) is a promising thermoelectric material and α-phase Cu2Se provides relatively safe thermoelectric modules for thin film thermoelectric device in contrast to some toxic materials currently on the market. In this work, nanocrystalline Cu2Se thin film with uniform element distribution was fabricated at room temperature through an effective combination reaction method by implanting sputtered Cu+ ions into Se precursor. Then, self-assembled growth of Cu2Se thin films with desired α-phase and well crystallinity was successfully achieved with optimization of annealing temperature. Interestingly, the growth orientation has obviously affected by the annealing temperature, which significantly affects the thermoelectric properties. Consequently, the Seebeck coefficients increase with the increase in the orientation factor of the (0l0) preferred orientation, which enhances power factor. The high maximum power factor of 9.23 μWcm−1K−2 is achieved for α-Cu2Se thin film with (0l0) preferred orientation, demonstrating that the method used in this work has great potential in developing low-cost and high-performance thermoelectric thin films from relatively earth-abundant elements. © 2021 Elsevier B.V.

International audience; Flexible thin-film thermoelectric devices have been extensively studied for powering wearable electronics, particularly as a power source for self-powered sensors or temperature detection. Skutterudite CoSb3 is emerging as one of the most studied candidate materials for thermoelectric applications. This work is focused on comprehensive optimization in terms of CoSb3-based thin films as well as electrode materials and structures with the objective to fabricate high-performance flexible devices. CoSb3-based thin films with nanoparticles for the enhancement of phonon scattering have been fabricated using the vacuum sputtering method. N-type and P-type thin films can be obtained by appropriate doping with Ti and In, respectively. It has been demonstrated that a multilayer structure of electrodes can greatly enhance the thermoelectric performance of thermoelectric devices by increasing the output power and the thermal stability of the device in the air atmosphere. It has also been demonstrated the possibility of obtaining a relatively high output voltage of above 90 mV and a high-power density of 0.46 mW/cm(2) at a current intensity of about 0.35 mA with the device. Therefore, many applications can be considered. The thin-film thermoelectric device has also been tested as a thermal sensor, and it exhibits fast responsivity, with a reaction time of a few hundreds of milliseconds, as well as high stability.

International audience; Flexible thermoelectric (TE) materials have wide applications in fabricating portable/wearable devices owing to the advantages of being bendable, small size, and lightweight. Inorganic material–based flexible thin films have attracted much attention owing to their high TE performance. So far, developing high TE properties and environment friendly flexible thin films for practical applications is still a considerable challenge. Copper selenide (Cu2Se) is a non-toxic and low-cost material, providing relatively safe TE modules for thin film devices. In this work, Cu2Se-based thin films with single crystal phase have been fabricated successfully at a flexible substrate by an efficient layer-by-layer combination reaction method. By optimizing the composition, a high power factor of 5.3 μWcm−1K−2 and dimensionless figure of merit value of 0.35 with low thermal conductivity are achieved at room temperature. Through bending tests, it has been shown that the prepared thin films possess good flexibility and the designed flexible device displays stable output power, which demonstrates the potential of inorganic TE materials to be mountable on flexible/wearable substrates for energy harvesting and management devices.

The effect of Pb and La substitution on the thermoelectric properties of BiCuSeO oxyselenide has been studied. It is revealed that Pb doping can significantly improve the electrical conductivity due to the increased carrier concentration, which results in a large power factor in the range of 700 to 800 μW m−1 K−2 at 873 K. In particular, the electrical transport properties can be further improved obviously over the entire measured temperature range after replacing some Bi3+ ions with La3+ ions in Bi0.94Pb0.06CuSeO. The electrical conductivity has increased from 408 S cm−1 for Bi0.94Pb0.06CuSeO to 594 S cm−1 for Bi0.93Pb0.06La0.01CuSeO at 327 K due to the increased carrier mobility. Combining with the moderate Seebeck coefficient which is over 124 μV K−1, the power factor has been significantly improved. An optimal value of 1059 μW m−1 K−2 at around room temperature is achieved for Bi0.93Pb0.06La0.01CuSeO and is much higher than most reported values. Additionally, the increased total thermal conductivity for the Pb-doped sample compared with the pristine sample has been suppressed after further doping the La element in Bi0.94Pb0.06CuSeO. Therefore, a maximum ZT value of nearly 0.90 at 873 K for the sample Bi0.92La0.02Pb0.06CuSeO has been finally obtained, which is ∼36% and ∼16% higher as compared with those of the La-free sample Bi0.94Pb0.06CuSeO and the reported Pb-free sample Bi0.92La0.08CuSeO.

An n-type Bi-doped SnSe was synthesized by a facile solution method followed by spark plasma sintering. We used bismuth(III) 2-ethyhexanoate as a cationic dopant precursor, which can absorb on the powder surface and then diffuse into the lattice to realize the substitution of Sn by Bi. A strip structure with low-angle boundary was constructed for effective phonon scattering. With increasing content of Bi, the carrier concentration decreased from 1.35 × 1019 cm-3 (p-type) in undoped SnSe to 4.7 × 1014 cm-3 (n-type) in Sn0.99Bi0.01Se and then increased to 1.3 × 1015 cm-3 (n-type) in Sn0.97Bi0.03Se. The Seebeck coefficient changed from positive to negative and presented n-type conducting behavior in the whole measured temperature range from 300 to 773 K, reaching a maximum absolute value of ∼900 μV K-1 at room temperature and ∼300 μV K-1 at 773 K. Considering the rich variety of metal 2-ethylhexanoates, higher thermoelectric performance is expected by different cationic doping in solution-synthesized nanomaterials.

Recently, fabrication of high-efficiency miniature thermoelectric devices with thin films has attracted great attention. ZnSb-based thin films have been widely studied owing to their advantages of earth-abundant, eco-friendly, and excellent electron transport properties. However, its thermoelectric performance at room temperature is still low which extremely restricts its application. In this work, we report a high-power factor of 6.2 μWcm −1K−2 and a record-high thermoelectric figure of merit, ZT of 0.35 at room temperature from the non-stoichiometric ZnSb-based thin film, fabricated by a facile magnetron cosputtering technique. Extensive characterizations reveal that all the prepared films have a primary ZnSb phase with good crystallinity, leading to high electrical conductivity . Meanwhile, the carrier concentration is optimized with Zn addition, which contributes to a high Seebeck coefficient, resulting in a decent power factor. Simultaneously, the Zn-rich films also show nanopores , Zn-rich nanophases, and Zn 4Sb3 nano inclusions. These induced nanostructures enhance the scattering of medium- and long-wavelength phonons, contributing to the reduction of lattice thermal conductivity . This work demonstrates that rational nanostructure manipulations can achieve high performance in ZnSb thin films, which possess potential applications for the fabrication of miniature thermoelectric devices.

The sulfide compound Bi2SeS2 is an environmentally friendly thermoelectric material, which is as an analogy of the traditional compound Bi2S3. Here, a high ZT value of 1.04 at 773 K is obtained through synergistically tuning the electrical transport properties by using Cu and I as the dual carrier providers and suppressing the lattice thermal conductivity by forming the Cu-rich nano-precipitates. The dual carrier providers lead to exclusively high electrical conductivity and hence a large power factor over 650 μWm−1K−2 at 773 K. The atomic resolved annular dark field STEM reveals the interstitial Cu and S deficiency would result into the formation of BiCuS2 or Cu2S nano-precipitates and embed in the lattice of Bi2SeS2, serving as strong phonon scattering. This work suggested that nanostructured Bi2SeS2 is very promising for waste heat energy harvesting in the future.

Earth-abundant IV–VI semiconductor SnSe is regarded as a promising thermoelectric material due to its intrinsic low thermal conductivity. In this report, the highly textured SnSe/Ag2Se composites were first designed by solid solution method followed by spark plasma sintering (SPS) and their thermoelectric properties in two directions were investigated, and then, the performance of composites was further optimized with an additional ball milling. The coexistence of SnSe and Ag2Se phases is clearly confirmed by energy-dispersive X-ray spectroscopy (EDX) in transmission electron microscopy (TEM). After ball milling, the size of SnSe grains as well as the incorporated Ag2Se particles reduces effectively, which synergistically optimizes the electrical and thermal transport properties at high temperature range. As a result, a maximum ZT of ~ 0.74 at 773 K for SnSe + 1.0%Ag2Se in the direction vertical to the pressing direction is achieved. Composite engineering with additional ball milling is thus proved to be an efficient way to improve the thermoelectric properties of SnSe, and this strategy could be applicable to other thermoelectric systems.

High thermoelectric performance of n-type PbTe is urgently needed to match its p-type counterpart. Here, we show a peak ZT ∼ 1.5 at 723 K and a record high average ZT > 1.0 at 300–873 K realized in n-type PbTe by synergistically suppressing lattice thermal conductivity and enhancing carrier mobility by introducing Cu2Te inclusions. Cu performs several outstanding roles: Cu atoms fill the Pb vacancies and improve carrier mobility, contributing to an unexpectedly high power factor of ∼37 μW cm–1 K–2 at 423 K; Cu atoms filling Pb vacancies and Cu interstitials both induce local disorder and, together with nano- and microscale Cu-rich precipitates and their related strain fields, lead to a very low lattice thermal conductivity of ∼0.38 Wm–1 K–1 in PbTe-5.5%Cu2Te, approaching the theoretical minimum value of ∼0.36 Wm–1 K–1. This work provides an effective strategy to enhance thermoelectric performance by simultaneously improving electrical and thermal transport properties.

Cu-Se compounds have attracted more attentions as a low-cost, low toxicity thermoelectric materials. In this work, p-type Cu 2 Se x compound powders were prepared by solution syntheses, including the wet chemistry method and hydrothermal synthesis method. The reaction mechanisms were investigated, showing that the NaOH contents affected the phase structure of the final product. Polycrystalline Cu 2 Se x bulk materials were obtained by densifying the powders using spark plasma sintering (SPS) and obtained the maximum ZT value of 0.75 at 623 K, which is currently the highest reported value for the Cu-Se system at this temperature. We also found that the introduced oxides could suppress the long-range migration of Cu ions in Cu-Se system to avoid the decomposition of the materials.

We report n-type PbTe with a maximum ZT ∼1.2 at 673 K and an average ZTave ∼0.84 at 300–823 K, which was achieved through a Sn and Se co-alloying approach. We find that the lattice thermal conductivity can be largely reduced through introducing Se in Te sites, and the power factor can be enhanced through introducing Sn in the Pb sites. Combining two strategies via Se and Sn co-alloying in PbTe, results show that the lattice thermal conductivity at 300 K can be reduced from ∼3.1 Wm−1K−1 to ∼1.2 Wm−1K−1 after alloying 15% Se, which is consistent with the Callaway model. Meanwhile, we find that both carrier concentration and mobility can be enhanced through alloying small amount of Sn, which are supported by DFT calculation with emphasis on the defect formation energies. The improvement on electrical conductivity elucidates an enhanced power factor at 300 K increasing from ∼6.4 μWcm−1K−2 to ∼14.6 μWcm−1K−2. Through synergistically optimizing electrical and thermal transport properties of n-type PbTe via Sn and Se co-alloying, the ZT value is distinctly enhanced to 1.2 at 673 K, and the average ZTave value is improved by ∼35%, from ∼0.62 in PbTe0.997I0.003 to ∼0.84 in Pb0.995Sn0.005Te0.847Se0.15I0.003, ensuring a high maximum thermoelectric conversion efficiency ∼10.7%.

Zr 2 W 2 P 2 O 15 with larger-negative-thermal-expansion-coefficient (NTEC, −4.01×10 −6 K −1 , 143–673 K) is developed by controlling reaction process to avoid the intermediate phase of Zr 2 WP 2 O 12 , whose smaller NTEC limits its application. From 1473 K to1573 K, Zr 2 WP 2 O 12 forms easily but the reaction between Zr 2 WP 2 O 12 and WO 3 to generate Zr 2 W 2 P 2 O 15 is difficult even followed by heating up to 1673 K. However, putting raw materials of ZrO 2 , WO 3 and NH 4 H 2 PO 4 into a pipe furnace at sintering temperature 1673 K directly, the Zr 2 W 2 P 2 O 15 is formed avoiding the intermediate phase of Zr 2 WP 2 O 12 .

SnTe, one lead-free analogue of PbTe, has been paid attention in thermoelectric community because it has the similar rock-salt crystal structure and electronic band structure. However, SnTe possesses a very high total thermal conductivity (∼10.0 W m−1 K−1 at room temperature) and a mediocre ZT (∼0.2 at 723 K). In this study, to reduce its thermal conductivity, we prepare SnTe samples by melting reaction followed by mechanical alloying and spark plasma sintering. We demonstrate that both total thermal conductivity and lattice thermal conductivity can be considerably reduced through reducing particle size from micro-scale to nano-scale via facially mechanical alloying method. Experimental results show that the total thermal conductivity at room temperature can be reduced from ∼10 W m−1 K−1 for SnTe ingot to ∼3Wm−1 K−1 for SnTe with mechanical alloying 25 h. Correspondingly, the lattice thermal conductivity at room temperature was reduced from ∼5Wm−1 K−1 to ∼2Wm−1 K−1. Combination of reduced thermal conductivity and moderate power factor, average ZTave can be increased by 33.3%, from 0.09 for SnTe ingot to 0.12 for SnTe with nano-grain size.