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Summary Thermoelectric technology provides an alternative way to utilize fossil energy more efficiently through converting the waste heat from industrial or automobile exhaust gas into electricity. The usual thermoelectric module design only needs to achieve high-energy conversion efficiency. This is not enough for many novel thermoelectric materials with low thermodynamic stability such as liquid-like materials and some Mg/Zn-containing compounds, which may lead to possible module instability during service. Here, we successfully achieve a thermoelectric module based on high-performance liquid-like materials with both good stability and high efficiency up to 9.1%, more than 50% higher than those made by half-Heusler and SiGe. A module’s stability is included in the design through tuning the geometry of the legs to ensure that the voltage applied on the liquid-like material is below the threshold for stable usage. This study provides an effective strategy to achieve efficient and stable modules based on various new thermoelectric materials.

Summary Lattice vibrations in crystalline materials generate phonons as heat carriers for heat conduction, and the phonon dispersion (energy versus momentum) is fundamentally determined by the mass of lattice vibrators (atoms) and the interaction force between atoms. A significant manipulation of lattice thermal conductivity through a change in atomic mass usually requires a large variation in chemical composition, which is not always valid thermodynamically or may risk the resultant detriment of other functionalities (e.g., carrier mobility). Here we show a strategy of alternatively manipulating the interaction force between atoms through lattice strains without changing the composition, for remarkably reducing the lattice thermal conductivity without reducing carrier mobility, in Na0.03Eu0.03Sn0.02Pb0.92Te with stable lattice dislocations. This successfully leads to an extraordinarily high thermoelectric figure of merit, with the help of valence band convergence. This work offers both insights and solutions on lattice strain engineering for reducing lattice thermal conductivity, thus advancing thermoelectrics.

GeTe-based compounds have been intensively studied recently due to their superior thermoelectric performance, but their real applications are still limited so far due to the drastic volume variation that occurs during the rhombohedral–cubic phase transition, which may break the material or the material/electrode interface during service. Here, superior performance and high service stability for GeTe-based thermoelectric compounds are achieved by co-doping Mg and Sb into GeTe. The linear coefficient of thermal expansion before phase transition is greatly improved to match that after phase transition, yielding smooth volume variation around the phase transition temperature. Likewise, co-doping (Mg, Sb) in GeTe successfully tunes the carrier concentration to the optimal range and effectively suppresses the lattice thermal conductivity. A peak zT of 1.84 at 800 K and an average zT of 1.2 in 300–800 K have been achieved in Ge0.85Mg0.05Sb0.1Te. Finally, a Ni/Ti/Ge0.85Mg0.05Sb0.1Te thermoelectric uni-leg is fabricated and tested, showing quite good service stability even after 450 thermal cycles between 473 K and 800 K. This study will accelerate the application of GeTe-based compounds for power generation in the mid-temperature range.

Half-Heusler compounds are a class of promising thermoelectric (TE) materials for power generation. However, the large contact resistivity at the interface between TE legs and metal electrode of the TE device seriously hinders the full play of the material performance. Here we report an Ohmic contact for the junction of p-type Nb0.8Ti0.2FeSb and Mo electrode with a low contact resistivity of

Herein, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) coated Cu xSe y (PC-Cu xSe y) nanowires are prepared by a wet-chemical method, and PEDOT:PSS/Cu xSe y nanocomposite films on flexible nylon membrane are fabricated by vacuum assisted filtration and then cold-pressing. XRD analysis reveals that the Cu xSe y with different compositions can be obtained by adjusting the nominal Cu/Se molar ratios of their sources. For the composite film starting from a Cu/Se nominal molar ratio of 3, an optimized power factor of ∼270.3 μW/mK2 is obtained at 300 K. Moreover, the film exhibits a superior flexibility with 85% of the original power factor retention after bending for 1000 cycles around a rod with a diameter of 5 mm. TEM and STEM observations of the focused ion beam (FIB) prepared sample reveal that it is mainly attributed to a synergetic effect of the nylon membrane and the composite film with nanoporous structure formed by the intertwined nanowires, besides the intrinsic flexibility of nylon. Finally, a thermoelectric prototype composed of nine legs of the optimized hybrid film generates a voltage and a maximum power of 15 mV and 320 nW, respectively, at a temperature gradient of 30 K. This work offers an effective approach for high TE performance inorganic/polymer composite film for flexible TE devices.

Liquid-like binary Cu2-δX (X = S, Se, and Te) chalcogenides and their ternary solid solutions have gained notable attention in thermoelectrics due to their interesting and abnormal thermal and electrical transport properties. However, previous studies mainly focus on a single element alloying at either an anion or cation site whereas the investigation on cation/anion co-alloying is very rare so far. Here, a series of quaternary Cu2-2 xAg2 xSe1- xS x ( x = 0.01, 0.03, 0.05, 0.1, 0.15) liquid-like copper chalcogenide materials have been fabricated and the effects of Ag/S co-alloying on the thermoelectric properties of Cu2Se have been systematically studied. It is found that all compounds are mixed phases at room temperature but single cubic phase at high temperatures. The introduction of Ag and S in Cu2Se brings about a large mass fluctuation rather than strain field fluctuation that effectively suppresses the lattice thermal conductivity. Furthermore, on increasing the Ag and S contents, the high electrical conductivity of pristine Cu2Se is well tuned to the optimal range derived from the single parabolic band model analysis. Consequently, a peak zT of 1.6 at 900 K is achieved in Cu1.8Ag0.2Se0.9S0.1, which is about 33% higher than that of binary Cu2Se.

Ag4SSe, named as aguilarite in mineralogy, belongs to the family of liquid-like superionic compounds at middle temperature, but its thermoelectric (TE) properties are rarely investigated so far. In this study, a series of Ag-deficient Ag4SSe samples have been synthesized by the melting–annealing method. Their crystal structures, phase transition features, and electrical and thermal transport properties have been systematically investigated. It is found that Ag4SSe allows a small amount of Ag deficiency inside the lattice without altering the initial crystal structure and phase transition feature. The stoichiometric Ag4SSe has a low TE figure of merit (zT) of 0.24 at 613 K because of the overhigh carrier concentration. Introducing Ag deficiency in Ag4SSe significantly lowers the carrier concentration, yielding a greatly enhanced Seebeck coefficient and suppressed carrier thermal conductivity throughout the entire measured temperature range. A maximum TE zT of 0.53 is achieved at 493 K for Ag3.96SSe, about ...

A novel trench SOI LDMOS with centrosymmetric double vertical field plates structure (CDVFPT SOI LDMOS) is proposed in this paper. The 2-D device simulator MEDICI is used to investigate the characteristics of the proposed structure. Compared with the conventional trench SOI LDMOS (CT SOI LDMOS), the optimized device shows an obvious reduction in the specific on-resistance (Ron,sp) when its breakdown voltage (BV) is enhanced due to the introduction of centrosymmetric double vertical field plates structure. And when compared to previous device with floating vertical field plate trench SOI LDMOS (FVFPT SOI LDMOS), the overall performance of CDVFPT SOI LDMOS is also promoted. According to the simulation results, compared to a CT SOI LDMOS, the BV of CDVFPT SOI LDMOS increases from 188 V to 234 V. The Ron,sp, however, decreases from 2.30 mΩ·cm2 to 1.24 mΩ·cm2. In addition, the maximum lattice temperature at 1 mW/μm2 is slightly reduced. Keywords: Power MOSFET, Vertical field plate, Breakdown voltage, Specific on-resistance

In this work, single-walled carbon nanotube (SWCNT)/PEDOT:PSS coated Te nanorod (PC-Te) composite films were prepared by a simple vacuum assisted filtration method, and H2SO4 treatment was employed to improve the thermoelectric performance of the composite films. The addition of SWCNTs apparently improved the electrical conductivity while reduced the Seebeck coefficient of the composite films, resulting in a reduction of the power factor. After treated with H2SO4, the electrical conductivity of the composite films was further improved, and the Seebeck coefficient decreased slightly. As a consequence, an optimized power factor of 104 μW/mK2 (corresponding to the electrical conductivity of 332 S/cm and Seebeck coefficient of 56 μV/K, respectively) was obtained for the sample containing 70 wt% SWCNTs at 300 K. A flexible thermoelectric generator prototype was fabricated to demonstrate the output properties. The open circuit voltage and maximum output power delivered from the prototype were 5.6 mV and 53.6 nW, respectively, at a temperature difference of 44 K.

Cu2Se based thermoelectric materials are of great potential for high-temperature energy harvesting due to their high-temperature figure-of-merit (zT). For further development of Cu2Se, both engineering and mid-temperature figure-of-merit need to be improved. In this work, we report that carbon-coated boron (C/B) nanoparticles incorporation can significantly improve both mid- and high-temperature zT in Cu2Se. The nanoparticle inclusions can result in a homogeneous distribution of Cu:C:B interfaces responsible for both improvement of the Seebeck coefficient and significantly reduction in thermal conductivity. Ultrahigh mid- and high temperature thermoelectric performance with zT=1.7 at 700K and 2.23 at 1000K as well as significantly improved engineering zT are achieved in the C/B incorporated Cu2Se with desirable mechanical properties and cycling stability. Our findings will stimulate further study and exploration for the Cu2Se based thermoelectric materials for broad applications in converting waste heat to electricity with competitive energy conversion efficiency.

Diffusion barrier materials play an important role in both structure reliability and performance stability of thermoelectric (TE) modules. Preferred barrier materials are screened out from various candidates by comparing the interdiffusion at the barrier material/TE substrate interfaces. Traditionally, for each barrier material candidate, complicated fabrication processing of TE elements (electrode/barrier material/TE material) must be finished to obtain relative interfaces, which makes the screening costly and time consuming. In this article, using a high-throughput strategy, we developed a high-efficiency screening method of barrier materials. By cosintering the mixture of TE substrate material and various barrier material candidates simply following the TE material’s sintering parameters, various microinterfaces were integrated to one single sample. This enables parallel aging and microstructure characterization of different interfaces, and preferred barrier materials can be swiftly screened out. As a result, it makes the design and optimization of TE modules much more efficient and economical.

To protect CoSb3-based skutterudite thermoelectric materials from oxidation and to suppress the sublimation of antimony in long-time service, a series of surface coatings including Al, Al-Ni, Al-Ni-Al were deposited onto Yb0.3Co4Sb12 by using an electrochemical deposition method. The thermal aging behavior for the Yb0.3Co4Sb12 samples with and without different surface coatings were investigated by accelerated thermal aging tests at 873 K. Thermoelectric properties of Yb0.3Co4Sb12 with different coatings after aging are used as the evaluation criteria for coating effectiveness. After thermal aging at 873 K for 30 days, the thermoelectric properties of Yb0.3Co4Sb12 coated with Al-Ni double-layered coating were almost undecreased, indicating that the Al-Ni coating is suitable for protecting CoSb3-based skutterudite from oxidation and for suppressing the sublimation of antimony. It is expected that this coating could improve the reliability of CoSb3-based devices and could accelerate the application of skutterudite thermoelectric generators.

Copper-based chalcogenides have ultralow thermal conductivity and ultrahigh thermoelectric performance, but most of them are p-type semiconductors. It is urgent to develop n-type counterparts for high efficiency thermoelectric modules based on these copper based-chalcogenides. Cu4Sn7S16 is an intrinsically n-type semiconductor with complex crystal structure and low thermal conductivity. However, its thermoelectric properties have not been well studied when compared to the well-known n-type CuFeS2. In this work, high-quality Cu4Sn7S16-based compounds are fabricated and their thermoelectric properties are systematically studied. Using Ag and Sb as dopants, the carrier concentration is tuned over a wide range. The electrical transport properties can be well described by the single parabolic band model with carrier acoustic phonons scattering. It is revealed that Cu4Sn7S16 exhibits a low effective mass and relatively high mobility. The thermal conductivity is lower than 0.8 W m−1 K−1 from 300 to 700 K and shows a weak dependence on temperature. A maximum zT of 0.27 is obtained in Cu3.97Ag0.03Sn7S16 at 700 K. Further enhancement of thermoelectric performance is possible when a more efficient n-type dopant is used.

PEDOT:PSS coated Te (PC Te) nanorod/PEDOT:PSS composite films were prepared by a drop-casting technique. H2SO4 treatment was employed to enhance thermoelectric (TE) properties of the composite films. The addition of PC Te nanorods increased both the electrical conductivity and the Seebeck coefficient of the composite films. An optimized power factor of 141.9 μW/mK2 was obtained for the film containing 90 wt% PC Te nanorods treated with 12 M H2SO4 at room temperature, which was 2.75 times as high as that of the untreated composite film, corresponding to the electrical conductivity and Seebeck coefficient of 204.6 S/cm and 83.27 μV/K, respectively. XPS and GIWAXS analysis revealed the removal of insulating PSS units and the rearrangement of PEDOT chains after the H2SO4 treatment. Finally, a 9-leg TE generator prototype was fabricated using the optimized composite film. The maximum output power and area output power density produced from the prototype were 47.7 nW and 57.2 μW/cm2, respectively, at the temperature difference of 40 K.

Combining high thermoelectric (TE) performance, excellent mechanical properties, and good thermal stability, half-Heusler materials show great potential in real applications, such as industrial waste heat recovery. However, the materials synthesis technology developed in the laboratory scale environment cannot fulfil the requirements of massive device fabrication. In this work, a batch synthesis utilizing the self-propagating high-temperature synthesis (SHS) method was used to prepare state-of-the-art n-type Zr0.5Hf0.5NiSn0.985Sb0.015 and p-type Zr0.5Hf0.5CoSb0.8Sn0.2 half-Heusler alloys. Due to the nonequilibrium reaction process, dense dislocation arrays were introduced in both n-type and p-type materials, which greatly depressed the lattice thermal conductivity. As a consequence, the zT values of samples cut from ingots weighing a few hundreds of grams compared favorably with those prepared from few gram laboratory size pellets. Based on the high TE performance, a three-dimensional finite element model encompassing all relevant parameters was applied to optimize the topological structures of both a half-Heusler single-stage module and a half-Heusler/Bi2Te3 segmented module. The optimized modules attained record-high conversion efficiencies of 9.6% and 12.4% for the single-stage and the segmented module, respectively. The work documents a comprehensive processing of novel TE materials culminating in the assembly of efficient TE modules. As such, it paves the way for widespread commercial applications of TE power generation.

Flexible thermoelectrics is a synergy of flexible electronics and thermoelectric energy conversion. To date, state-of-the-art thermoelectrics is based on inorganic semiconductors that afford high electron mobility but lack in mechanical flexibility. By contrast, organic materials are amply flexible but low in electrical mobility and power output; the inorganic–organic hybrid design is a viable material-level option but has critical device-level issues for practical application. Here, we reported high intrinsic flexibility and state-of-the-art figures of merit (up to 0.44 at 300 K and 0.63 at 450 K) in Ag2S-based inorganic materials, opening a new avenue of flexible thermoelectrics. In the flexible full-inorganic devices made of such Ag2S-based materials, high electrical mobility yielded a normalized maximum power density up to 0.08 W m−1 under a temperature difference of 20 K near room temperature, orders of magnitude higher than organic devices and organic–inorganic hybrid devices. These results promised an emerging paradigm and market of wearable thermoelectrics.

β-FeSi2, a semiconductor material made of two of the most earth-abundant elements, has important applications in thermoelectrics, photovoltaics and optoelectronics owing to its attractive properties such as suitable band gap and air stability over a wide temperature range. While point defects always play a vital role in semiconductor materials, only sporadic studies have been dedicated to the defects in β-FeSi2. Here, using first-principles calculations we systematically investigate the intrinsic point defects in β-FeSi2. Our results reveal that the formation energies of the intrinsic defects in β-FeSi2 are high enough to prevent them from forming in a significant concentration under thermal equilibrium growth conditions. As a possible kinetic process generating intrinsic defects, we study the α-to-β phase transition of FeSi2. We find that the phase transition is a slow process occurring on the time scale of an hour. Incomplete phase transition may lead to kinetically formed intrinsic defects. We further calculate the activation energies of the intrinsic defects and show that the experimentally observed conductivity of pure β-FeSi2 should be a result of unintentional doping. Possible extrinsic impurities that may lead to n-type and p-type conductivity and their activation energies are calculated, which are in good agreement with available experiments. Our results provide guidance for optimizing the doping strategy of β-FeSi2 for device applications.

Two-dimensional porous carbon nanosheet materials are of increasing importance. Many examples for their synthesis exist, but they generally show some common requirements, such as rigid reaction conditions, high cost and complicated multiple synthetic steps. Here we report a facile and cost-effective way to prepare porous carbon nanosheets by using an exfoliated nanopaper-like biomass, i.e., melaleuca bark as precursor. It is found that just after a simple carbonization treatment, the nanopaper-like barks can be directly transformed into two-dimensional carbon nanosheets with a unique hierarchical porous structure. A high BET surface area of 1397 m2/g can be reached for the obtained carbon materials without any extra activation process. Tuning of nanostructures could be facilely accomplished by varying carbonization treatment conditions. The as-prepared porous carbon nanosheet serves well as the sulfur host materials for lithium-sulfur battery.

Herein, we demonstrate a concept of making flexible thermoelectric (TE) generators by applying cotton thread as the platforms for poly(3-hexylthiophene) (P3HT) and Argentum (Ag) paste through selectable coating method. The coated thermoelectric cotton thread can be sewed on the flexible fabrics with different knitting pictures and form thermoelectric devices. The most important is that the temperature gradient of the device was in the direction of cross-plane of the flexible fabrics, that is, between the inner and outer surfaces of clothing, therefore the flexible device can be easily wore on the body since the temperature gradient between the human body and surrounding environment is in the cross-plane direction. The maximum output power of the device with thirteen P N type legs reached 1.15 μW at a temperature gradient of 50 K when the load resistance matched the resistance of the module. Cotton-based TE device coated with P3HT may be useful for the development of self-powered wearable electronics.

Physics letters / B 103(17), 174515 (2021). doi:10.1103/PhysRevB.103.174515, The application of pressure has been speculated to boost the search for high-temperature superconductors, especially in superhydrides. However, the applied pressure as high as hundreds of GPa needed to create superconductivity in those materials limits their technological application. Finding a route to achieve the high-temperature superconductivity at near-ambient conditions is attractive. By choosing a phase-change alloy Ge$_2$Sb$_2$Te$_5$, we study the phase evolution of this material with pressure from the trigonal phase through the amorphous to the body-centered cubic one by the measurements of x-ray diffraction, Raman scattering, resistivity, and Hall coefficient. Superconductivity is observed to take place in the last two phases and can maintain at nearly ambient pressure in the decompression run. Pressure-induced disorder is found to be the key for holding superconductivity in the compressed phase-change alloy., Published by North-Holland Publ., Amsterdam

Bismuth telluride alloys have dominated the industrial application of thermoelectric cooling, but the relatively poor mechanical performance of commercial zone-melting material seriously limits the device integration and stability. Here, we exhibit synergistically enhanced thermoelectric and mechanical performances of sintered Bi

Discovering novel materials and attaining higher performance are the eternal pursuit of thermoelectric materials research. Here, we report a material series, (Cu1−xAgx)2(Te1−ySy) (0.16 ≤ x ≤ 0.24, 0.16 ≤ y ≤ 0.24), which adopts a complex orthorhombic structure differing from any known crystal structure of (Cu/Ag)2(S/Te). This material series is featured by the crystal-amorphicity duality induced by the large anionic size mismatch: a crystalline sublattice of highly size-mismatched anions Te/S coexists with an amorphous-like sublattice of cations Cu/Ag. In the context of structure-property correlation, the crystal-amorphicity duality gave rise to not only interesting electrical properties but also exceptionally low lattice thermal conductivities from 300 to 1,000 K. A state-of-the-art figure of merit zT of 2.0 is obtained in the x = y = 0.22 sample at 1,000 K. These results give insights into crystal-amorphicity duality as a paradigm-shifting materials design approach to develop high-performance thermoelectric materials.

Manipulations of carrier and phonon scatterings through hierarchical structures have been proved to be effective in improving thermoelectric performance. Previous efforts in GeTe-based materials mainly focus on simultaneously optimizing the carrier concentration and band structure. In this work, a synergistic strategy to tailor thermal and electrical transport properties of GeTe by combination with the scattering effects from both Ge vacancies and other defects is reported. The addition of Fe in GeTe-based compounds introduces the secondary phase of FeGe

Precise localization and pose estimation in indoor environments are commonly employed in a wide range of applications, including robotics, augmented reality, and navigation and positioning services. Such applications can be solved via visual-based localization using a pre-built 3D model. The increase in searching space associated with large scenes can be overcome by retrieving images in advance and subsequently estimating the pose. The majority of current deep learning-based image retrieval methods require labeled data, which increase data annotation costs and complicate the acquisition of data. In this paper, we propose an unsupervised hierarchical indoor localization framework that integrates an unsupervised network variational autoencoder (VAE) with a visual-based Structure-from-Motion (SfM) approach in order to extract global and local features. During the localization process, global features are applied for the image retrieval at the level of the scene map in order to obtain candidate images, and are subsequently used to estimate the pose from 2D-3D matches between query and candidate images. RGB images only are used as the input of the proposed localization system, which is both convenient and challenging. Experimental results reveal that the proposed method can localize images within 0.16 m and 4° in the 7-Scenes data sets and 32.8% within 5 m and 20° in the Baidu data set. Furthermore, our proposed method achieves a higher precision compared to advanced methods.

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Hetero-shaped thermoelectric (TE) generators (TEGs) can power the sensors used in safety monitoring systems of undersea oil pipelines, but their development is greatly limited by the lack of materials with both good shape-conformable ability and high TE performance. In this work, a new ductile inorganic TE material, Ag

The rapid development of intelligent vehicles brings new challenges to vehicle EMC design, which is benefited from test data-oriented troubleshooting. With the increase in electronic complexity, vehicle on-board system designers should confront with more and more EMC failure possibilities and are in need of effective EMC failure diagnosis approach. However, EMC fault diagnosis is difficult due to the distinguishing features of EMC test dataset, such as small sample, nonlinear, high dimensions, etc. Hence, in this paper, EMC reverse diagnostic model is proposed. Firstly, EMC feature extraction method is designed. Then SVM model is designed to realize EMC faults classification. Corresponding application effect is displayed. Experiment results show that proposed method could match the demand of EMC fault diagnosis for intelligent vehicles.

In this work, we report a series of Cu

Self-powered wearable electronics require thermoelectric materials simultaneously with a high dimensionless figure of merit ( z T ) and good flexibility to convert the heat discharged by the human body into electricity. Ag 2 (S,Se)-based semiconducting materials can well satisfy these requirements, and thus, they are attracting great attention in thermoelectric society recently. Ag 2 (S,Se) crystalizes in an orthorhombic structure or monoclinic structure, depending on the detailed S/Se atomic ratio, but the relationship between its crystalline structure and mechanical/thermoelectric performance is still unclear to date. In this study, a series of A g 2 S e 1 ‐ x S x ( x = 0 , 0.1, 0.2, 0.3, 0.4, and 0.45) samples were prepared and their mechanical and thermoelectric performance dependence on the crystalline structure was systematically investigated. x = 0.3 in the A g 2 S e 1 ‐ x S x system was found to be the transition boundary between orthorhombic and monoclinic structures. Mechanical property measurement shows that the orthorhombic A g 2 S e 1 ‐ x S x samples are brittle while the monoclinic Ag 2 Se 1‐ x S x samples are ductile and flexible. In addition, the orthorhombic A g 2 S e 1 ‐ x S x samples show better electrical transport performance and higher z T than the monoclinic samples under a comparable carrier concentration, most likely due to their weaker electron-phonon interactions. This study sheds light on the further development of flexible inorganic TE materials.

Thermal conductivity is one of the most fundamental properties of materials with the value being determined by nearly all-scale structural features and multiple physical processes. Rapidly judging material’s thermal conductivity is extremely important but challenging for the applications. The material genome paradigm offers a revolutionary way to efficiently screen and discover materials with designed properties by using accessible indicators. But such a performance indicator for thermal conductivity is quite difficult to propose due to the existence of multiple mechanisms and processes, especially for the materials with complex structures such as chalcogenides. In this study, the number mismatch between cations and anions is proposed as a practical performance indicator for lattice thermal conductivity in complex copper and silver chalcogenides, which can be used to explain the observed experimental data and find new low thermal conductivity materials. Such a number mismatch brings about rich phenomena to affect thermal conductivity including the complication of the unit cell and the creation of chemical hierarchy, point defects, rattling modes and lone-pair electrons. It is expected that this rich-connotation performance indicator can be also extended to other complex materials to discover designed thermal conductivities.

High in-plane anisotropies arise in layered materials with large structural difference along different in-plane directions. We report an extreme case in layered TiS3, which features tightly bonded atomic chains along the b-axis direction, held together by weaker, interchain bonding along the a-axis direction. Experiments show thermal conductivity along the chain twice as high as between the chain, an in-plane anisotropy higher than any other layered materials measured to date. We found that in contrast to most other materials, optical phonons in TiS3 conduct an unusually high portion of heat (up to 66% along the b-axis direction). The large dispersiveness of optical phonons along the chains, contrasted to many fewer dispersive optical phonons perpendicular to the chains, is the primary reason for the observed high anisotropy in thermal conductivity. The finding discovers materials with unusual thermal conduction mechanism, as well as provides new material platforms for potential heat-routing or heat-managing devices.

Since vertical planes and lines are rich and unique for indoor localization, such as walls, posters, frames of doors and windows, a lightweight hybrid modeling method based on simple spatial features is proposed, specifically for the indoor localization and navigation applications. Firstly, the vertical planes in 3D space are detected and projected to generate a simplified floor plan of indoor environment. Here, a strategy of region segmentation and georeferencing is employed. Moreover, the plane-based model is further optimized by iterative merging algorithm. Then, some remarkable vertical lines are detected and localized based on the plane-based model, which can compensate the inaccuracy of plane ranges and the deficiency of remarkable planes in some areas. The dynamic time warping (DTW) algorithm is applied to match homonymous lines between sequential image frames, in cooperation with Kalman filtering for simultaneous tracking of vertical lines. Finally, a hybrid indoor model consisting of vertical planes and lines is generated, which is much more lightweight than previous 3D modeling methods. Experiments in real indoor scenes using single off-the-shelf smartphone verify the feasibility and effectiveness of the proposed method. The whole model size of an indoor environment with more than 200m2 area is only 302 Bytes, and it achieves an accuracy of about 0.3 meters.

Copper sulfides have attracted great attention recently in the thermoelectric community due to the liquid-like behavior of Cu ions. Among the numerous copper sulfides, digenite Cu1.80S has a poorer thermoelectric performance but better stability than the state-of-the-art binary copper sulfide Cu1.97S. In this study, good stability and high thermoelectric performance were simultaneously obtained in Fe-doped Cu1.80S. Because Fe ions will not form a concentration gradient under an external field to change the critical voltage, Fe-doped Cu1.80S samples inherit the good stability of the pristine Cu1.80S. The critical voltage for Cu1.80Fe0.064S is 0.16 V at 750 K, which has been the largest value reported so far. Likewise, the Fe dopants can significantly improve the thermoelectric performance by suppressing the too high electrical conductivity of Cu1.80S. The peak dimensionless figure of merit (zT) for Cu1.80Fe0.064S is around 0.8 at 750 K, about four times that of Cu1.80S. The average zT for Cu1.80Fe0.064S is 0.40 in 300-750 K, which is amongst the highest values in reported thermoelectric sulfides. Combining the good stability and high thermoelectric performance, the present Cu1.80Fe0.064S has great potential to be used in the application of waste heat harvesting in the middle temperature range.

β-FeSi

Deformable semiconductors Semiconductors are usually brittle and do not deform easily. Wei et al. found that bulk single crystals of indium selenide instead have excellent flexibility (see the Perspective by Han). The deformability comes from the compliant intralayer bonding between indium and selenium. The authors used these observations along with a previously discovered silver sulfide to determine a deformability factor for materials that may help find other deformable semiconductors. Science , this issue p. 542 ; see also p. 509