Extraordinary n‐Type Mg3SbBi Thermoelectrics Enabled by Yttrium Doping

Advancing thermoelectric n‐type Mg₃Sb₂ alloys requires both high carrier concentration offered by effective doping and high carrier mobility enabled by large grains. Existing research usually involves chalcogen doping on the anion sites, and the resultant carrier concentration reaches ≈3 × 10¹⁹ cm^?3 or below. This is much lower than the optimum theoretically predicted, which suggets that further improvements will be possible once a highly efficient dopant is found. Yttrium, a trivalent dopant, is shown to enable carrier concentrations up to and above ≈1 × 10²⁰ cm^?3 when it is doped on the cation site. Such carrier concentration allows for in‐depth understand of the electronic transport properties over a broad range of carrier concentrations, based on a single parabolic band approximation. As well as reasonably high carrier mobility in coarse‐grain materials sintered by hot deforming and fusing of large pieces of ingots synthesized by melting, higher thermoelectric performance than earlier experimentally reported for n‐type Mg₃Sb₂ is found. In particular, the thermoelectric figure of merit, zT, is even higher than that of any known n‐type thermoelectric, including Bi₂Te₃ alloys, within 300–500 K. This might pave the way for Mg₃Sb₂ alloys to become a realistic material for n‐type thermoelectrics for sustainable applications.     

Mg Compensating Design in the Melting-Sintering Method For High-Performance Mg3(Bi,Sb)2 Thermoelectric Devices

N-type Mg₃(Bi, Sb)₂-based thermoelectric (TE) alloys show great promise for solid-state power generation and refrigeration, owing to their excellent figure-of-merit (ZT) and using cheap Mg. However, their rigorous preparation conditions and poor thermal stability limit their large-scale applications. Here, this work develops an Mg compensating strategy to realize n-type Mg₃(Bi, Sb)₂ by a facile melting-sintering approach. “2D roadmaps” of TE parameters versus sintering temperature and time are plotted to understand the Mg-vacancy-formation and Mg-diffusion mechanisms. Under this guidance, high weight mobility of 347 cm² V⁻¹ s⁻¹ and power factor of 34 µW cm⁻¹ K⁻² can be obtained for Mg_3.05Bi_1.99Te_0.01, and a peak ZT≈1.55 at 723 K and average ZT≈1.25 within 323–723 K can be obtained for Mg_3.05(Sb_0.75Bi_0.25)_1.99Te_0.01. Moreover, this Mg compensating strategy can also improve the interfacial connecting and thermal stability of corresponding Mg₃(Bi, Sb)₂/Fe TE legs. As a consequence, this work fabricates an 8-pair Mg₃Sb₂-GeTe-based power-generation device reaching an energy conversion efficiency of ≈5.0% at a temperature difference of 439 K, and a one-pair Mg₃Sb₂-Bi₂Te₃-based cooling device reaching −10.7 °C at the cold side. This work paves a facile way to obtain Mg₃Sb₂-based TE devices at low cost and also provides a guide to optimize the off-stoichiometric defects in other TE materials.     

Metallic n-Type Mg3Sb2 Single Crystals Demonstrate the Absence of Ionized Impurity Scattering and Enhanced Thermoelectric Performance

Mg₃(Sb,Bi)₂ alloys have recently been discovered as a competitive alternative to the state-of-the-art n-type Bi₂(Te,Se)₃ thermoelectric alloys. Previous theoretical studies predict that single crystals Mg₃(Sb,Bi)₂ can exhibit higher thermoelectric performance near room temperature by eliminating grain boundary resistance. However, the intrinsic Mg defect chemistry makes it challenging to grow n-type Mg₃(Sb,Bi)₂ single crystals. Here, the first thermoelectric properties of n-type Te-doped Mg₃Sb₂ single crystals, synthesized by a combination of Sb-flux method and Mg-vapor annealing, is reported. The electrical conductivity and carrier mobility of single crystals exhibit a metallic behavior with a typical T^−1.5 dependence, indicating that phonon scattering dominates the charge carrier transport. The absence of any evidence of ionized impurity scattering in Te-doped Mg₃Sb₂ single crystals proves that the thermally activated mobility previously observed in polycrystalline materials is caused by grain boundary resistance. Eliminating this grain boundary resistance in the single crystals results in a large enhancement of the weighted mobility and figure of merit zT by more than 100% near room temperature. This work experimentally demonstrates the accurate understanding of charge-carrier scattering is crucial for developing high-performance thermoelectric materials and indicates that single-crystalline Mg₃(Sb,Bi)₂ solid solutions can exhibit higher zT compared to polycrystalline samples.     

Mg含量对Mg3(1+z)Sb2化合物热电传输性能的影响

Mg₃Sb₂化合物具有良好的热电性能和成本优势, 受到研究者的广泛关注。由于Mg元素具有很高的饱和蒸汽压和化学反应活性, 因此Mg₃Sb₂在合成过程中含量难以精确控制。本研究利用固相反应/球磨结合放电等离子体烧结制备了不同Mg含量的Mg_3(1+z)Sb₂(z=0, 0.02, 0.04, 0.06和0.08)样品, 通过物相结构分析和热电性能测试, 研究了Mg含量对Mg₃Sb₂化合物热电性能的影响规律。结果表明, 随着名义Mg含量的增加, 实际Mg含量在Mg₃Sb₂化合物中由缺失状态转变为过量状态, Mg_3(1+z)Sb₂(z=0, 0.02, 0.04)样品存在Mg空位(${{\text{{V}'}}_{\text{Mg}}}$), 表现为p型传导; 而Mg_3(1+z)Sb₂ (z=0.06, 0.08)样品中存在间隙Mg($\text{Mg}_{\text{i}}^{\centerdot \centerdot }$), 表现为n型传导。Mg_3(1+0.04)Sb₂样品在较宽温区(室温至770 K)内保持最高的热电优值, 该样品最接近本征p型Mg₃Sb₂化合物的组成和热电性能。本研究表明, Mg含量对Mg_3(1+z)Sb₂化合物载流子类型和浓度以及迁移率具有一定的调控作用。     

Chemical Vapor Deposition Growth of High Crystallinity Sb2Se3 Nanowire with Strong Anisotropy for Near‐Infrared Photodetectors

Low‐dimensional semiconductors have attracted considerable attention due to their unique structures and remarkable properties, which makes them promising materials for a wide range of applications related to electronics and optoelectronics. Herein, the preparation of 1D Sb₂Se₃ nanowires (NWs) with high crystal quality via chemical vapor deposition growth is reported. The obtained Sb₂Se₃ NWs have triangular prism morphology with aspect ratio range from 2 to 200, and three primary lattice orientations can be achieved on the sixfold symmetry mica substrate. Angle‐resolved polarized Raman spectroscopy measurement reveals strong anisotropic properties of the Sb₂Se₃ NWs, which is also developed to identify its crystal orientation. Furthermore, photodetectors based on Sb₂Se₃ NW exhibit a wide spectral photoresponse range from visible to NIR (400–900 nm). Owing to the high crystallinity of Sb₂Se₃ NW, the photodetector acquires a photocurrent on/off ratio of about 405, a responsivity of 5100 mA W^?1, and fast rise and fall times of about 32 and 5 ms, respectively. Additionally, owing to the anisotropic structure of Sb₂Se₃ NW, the device exhibits polarization‐dependent photoresponse. The high crystallinity and superior anisotropy of Sb₂Se₃ NW, combined with controllable preparation endows it with great potential for constructing multifunctional optoelectronic devices.     

Simple synthesis of a porous Sb/Sb2O3 nanocomposite for a high-capacity anode material in Na-ion batteries

High-capacity anode materials are highly desirable for sodium ion batteries.Here,a porous Sb/Sb2O3 nanocomposite is successfully synthesized by the mild oxidization of Sb nanocrystals in air.In the composite,Sb contributes good conductivity and Sb2O3 improves cycling stability,particularly within the voltage window of 0.02-1.5 V.It remains at a reversible capacity of 540 mAh·g-1 after 180 cycles at 0.66 A·g-L Even at 10 A·g-1,the reversible capacity is still preserved at 412 mAh.g-1,equivalent to 71.6％ of that at 0.066 A.g-1.These results are much better than Sb nanocrystals with a similar size and structure.Expanding the voltage window to 0.02-2.5 V includes the conversion reaction between Sb2O3 and Sb into the discharge/charge profiles.This would induce a large volume change and high structure strain/stress,deteriorating the cycling stability.The identification of a proper voltage window for Sb/Sb2O3 paves the way for its development in sodium ion batteries.     

Highly Efficient 2D/3D Hybrid Perovskite Solar Cells via Low‐Pressure Vapor‐Assisted Solution Process

The fabrication of multidimensional organometallic halide perovskite via a low‐pressure vapor‐assisted solution process is demonstrated for the first time. Phenyl ethyl‐ammonium iodide (PEAI)‐doped lead iodide (PbI₂) is first spin‐coated onto the substrate and subsequently reacts with methyl‐ammonium iodide (MAI) vapor in a low‐pressure heating oven. The doping ratio of PEAI in MAI‐vapor‐treated perovskite has significant impact on the crystalline structure, surface morphology, grain size, UV–vis absorption and photoluminescence spectra, and the resultant device performance. Multiple photoluminescence spectra are observed in the perovskite film starting with high PEAI/PbI₂ ratio, which suggests the coexistence of low‐dimensional perovskite (PEA₂MA_n?1Pb_nI_3n+1) with various values of n after vapor reaction. The dimensionality of the as‐fabricated perovskite film reveals an evolution from 2D, hybrid 2D/3D to 3D structure when the doping level of PEAI/PbI₂ ratio varies from 2 to 0. Scanning electron microscopy images and Kelvin probe force microscopy mapping show that the PEAI‐containing perovskite grain is presumably formed around the MAPbI₃ perovskite grain to benefit MAPbI₃ grain growth. The device employing perovskite with PEAI/PbI₂ = 0.05 achieves a champion power conversion efficiency of 19.10% with an open‐circuit voltage of 1.08 V, a current density of 21.91 mA cm^?2, and a remarkable fill factor of 80.36%.     

Breaking the Minimum Limit of Thermal Conductivity of Mg3Sb2 Thermoelectric Mediated by Chemical Alloying Induced Lattice Instability

Thermal properties strongly affect the applications of functional materials, such as thermal management, thermal barrier coatings, and thermoelectrics. Thermoelectric (TE) materials must have a low lattice thermal conductivity to maintain a temperature gradient to generate the voltage. Traditional strategies for minimizing the lattice thermal conductivity mainly rely on introduced multiscale defects to suppress the propagation of phonons. Here, the origin of the anomalously low lattice thermal conductivity is uncovered in Cd-alloyed Mg₃Sb₂ Zintl compounds through complementary bonding analysis. First, the weakened chemical bonds and the lattice instability induced by the antibonding states of 5p-4d levels between Sb and Cd triggered giant anharmonicity and consequently increased the phonon scattering. Moreover, the bond heterogeneity also augmented Umklapp phonon scatterings. Second, the weakened bonds and heavy element alloying softened the phonon mode and significantly decreased the group velocity. Thus, an ultralow lattice thermal conductivity of ≈0.33 W m⁻¹ K⁻¹ at 773 K is obtained, which is even lower than the predicated minimum value. Eventually, Na_0.01Mg_1.7Cd_1.25Sb₂ displays a high ZT of ≈0.76 at 773 K, competitive with most of the reported values. Based on the complementary bonding analysis, the work provides new means to control thermal transport properties through balancing the lattice stability and instability.     

Realizing zT of 2.3 in Ge1−x−ySbxInyTe via Reducing the Phase‐Transition Temperature and Introducing Resonant Energy Doping

GeTe with rhombohedral‐to‐cubic phase transition is a promising lead‐free thermoelectric candidate. Herein, theoretical studies reveal that cubic GeTe has superior thermoelectric behavior, which is linked to (1) the two valence bands to enhance the electronic transport coefficients and (2) stronger enharmonic phonon–phonon interactions to ensure a lower intrinsic thermal conductivity. Experimentally, based on Ge_1?xSb_xTe with optimized carrier concentration, a record‐high figure‐of‐merit of 2.3 is achieved via further doping with In, which induces the distortion of the density of states near the Fermi level. Moreover, Sb and In codoping reduces the phase‐transition temperature to extend the better thermoelectric behavior of cubic GeTe to low temperature. Additionally, electronic microscopy characterization demonstrates grain boundaries, a high‐density of stacking faults, and nanoscale precipitates, which together with the inevitable point defects result in a dramatically decreased thermal conductivity. The fundamental investigation and experimental demonstration provide an important direction for the development of high‐performance Pb‐free thermoelectric materials.     

Dual‐Phase CsPbBr3–CsPb2Br5 Perovskite Thin Films via Vapor Deposition for High‐Performance Rigid and Flexible Photodetectors

Inorganic perovskites with special semiconducting properties and structures have attracted great attention and are regarded as next generation candidates for optoelectronic devices. Herein, using a physical vapor deposition process with a controlled excess of PbBr₂, dual‐phase all‐inorganic perovskite composite CsPbBr₃–CsPb₂Br₅ thin films are prepared as light‐harvesting layers and incorporated in a photodetector (PD). The PD has a high responsivity and detectivity of 0.375 A W^?1 and 10¹¹ Jones, respectively, and a fast response time (from 10% to 90% of the maximum photocurrent) of ≈280 µs/640 µs. The device also shows an excellent stability in air for more than 65 d without encapsulation. Tetragonal CsPb₂Br₅ provides satisfactory passivation to reduce the recombination of the charge carriers, and with its lower free energy, it enhances the stability of the inorganic perovskite devices. Remarkably, the same inorganic perovskite photodetector is also highly flexible and exhibits an exceptional bending performance (>1000 cycles). These results highlight the great potential of dual‐phase inorganic perovskite films in the development of optoelectronic devices, especially for flexible device applications.     

67 Pb(Mg1/3Nb2/3)O3-33PbTiO3单晶90铁电畴光学研究

采用偏光显微镜观察了67Pb(Mg1/3Nb2/3)O3-33PbTiO3固溶体铁电单晶在室温时90铁电畴结构.铁电畴结构与晶体质量有关,在正交偏光显微镜下光学透明晶体中存在着尺寸为23mm的均匀大畴,不同极化方向的大畴重叠形成雾状区,使晶体表现出光学质量宏观不均匀.在光学质量差的雾状晶体中则存在着0.1mm宽的110型带状孪生畴,使晶体形成表面浮凸,带状畴内还存在着90°亚畴.并对这些畴的形成作了讨论     

Impact of Stoichiometry on the Structure of van der Waals Layered GeTe/Sb2Te3 Superlattices Used in Interfacial Phase‐Change Memory (iPCM) Devices

Van der Waals layered GeTe/Sb₂Te₃ superlattices (SLs) have demonstrated outstanding performances for use in resistive memories in so‐called interfacial phase‐change memory (iPCM) devices. GeTe/Sb₂Te₃ SLs are made by periodically stacking ultrathin GeTe and Sb₂Te₃ crystalline layers. The mechanism of the resistance change in iPCM devices is still highly debated. Recent experimental studies on SLs grown by molecular beam epitaxy or pulsed laser deposition indicate that the local structure does not correspond to any of the previously proposed structural models. Here, a new insight is given into the complex structure of prototypical GeTe/Sb₂Te₃ SLs deposited by magnetron sputtering, which is the used industrial technique for SL growth in iPCM devices. X‐ray diffraction analysis shows that the structural quality of the SL depends critically on its stoichiometry. Moreover, high‐angle annular dark‐field‐scanning transmission electron microscopy analysis of the local atomic order in a perfectly stoichiometric SL reveals the absence of GeTe layers, and that Ge atoms intermix with Sb atoms in, for instance, Ge₂Sb₂Te₅ blocks. This result shows that an alternative structural model is required to explain the origin of the electrical contrast and the nature of the resistive switching mechanism observed in iPCM devices.