Topological Electronic Transition Contributing to Improved Thermoelectric Performance in p-Type Mg3Sb2- xBix Solid Solutions.

Topological electronic transition is the very promising strategy for achieving high band degeneracy (NV) and for optimizing thermoelectric performance. Herein, this work verifies in p-type Mg3Sb2- xBix that topological electronic transition could be the key mechanism responsible for elevating the NV of valence band edge from 1 to 6, leading to much improved thermoelectric performance. Through comprehensive spectroscopy characterizations and theoretical calculations of electronic structures, the topological electronic transition from trivial semiconductor is unambiguously demonstrated to topological semimetal of Mg3Sb2- xBix with increasing the Bi content, due to the strong spin-orbit coupling of Bi and the band inversion. The distinct evolution of Fermi surface configuration and the multivalley valence band edge with NV of 6 are discovered in the Bi-rich compositions, while a peculiar two-step band inversion is revealed for the first time in the end compound Mg3Bi2. As a result, the optimal p-type Mg3Sb0.5Bi1.5 simultaneously obtains a positive bandgap and high NV of 6, and thus acquires the largest thermoelectric power factor of 3.54 and 6.93 µW cm-1 K-2 at 300 and 575 K, respectively, outperforming the values in other compositions. This work provides important guidance on improving thermoelectric performance of p-type Mg3Sb2- xBix utilizing the topological electronic transition.

Electrically Triggered Domain Wall Movement in Cu2Se Semiconductor.

The ion-conductive α-Cu2Se is found to possess antipolar dipoles, and the movement of the domain boundary under the applied voltage causes change of resistance, showing promising application in memristors. However, due to the complex ordering of Cu ions in the α-Cu2Se, there are multiple types of domain wall structure. Here, we show that two typical domain walls in α-Cu2Se can be formed, by controlling the voltage during phase transition from high-temperature cubic ß-Cu2Se to α-Cu2Se. We also show by in situ transmission electron microscopy that the formed [01̅0]/[101̅] domain wall performs a reversible movement under the applied external voltage, while the [010]/[01̅0] domain wall does not move. We further demonstrate that pinning of the [010]/[01̅0] domain wall could be due to the formed dislocations in the interface. This study shows that applying preprocess conditions is important to obtain the designed microstructure and resistive properties of α-Cu2Se.

Excellent Room Temperature Thermoelectric Performance in Mg3 Sb2 -Based Alloys via Multi-Functional Doping of Nb.

Mg3 Sb2 -based alloys are attracting increasing attention due to the excellent room temperature thermoelectric properties. However, due to the presence and easy segregation of charged Mg vacancies, the carrier mobility in Mg3 Sb2 -based alloys is always severely compromised that significantly restricts the room temperature performance. General vacancy compensation strategies cannot synergistically optimize the complicated Mg3 Sb2 structures involving both interior and boundary scattering. Herein, due to the multi-functional doping effect of Nb, the electron scattering inside and across grains is significantly suppressed by inhibiting the accumulation of Mg vacancies, and leading to a smooth transmission channel of electrons. The increased Mg vacancies migration barrier and optimized interface potential are also confirmed theoretically and experimentally, respectively. As a result, a leading room temperature zT of 1.02 is achieved. This work reveals the multi-functional doping effect as an efficient approach in improving room temperature thermoelectric performance in complicated defect/interface associated Mg3 Sb2 -based alloys.

Nature of Thermal Hysteresis of Thermoelectric Properties in Ag2TexS1-x Compounds.

Ag2TexS1-x usually undergo various phase structures upon heating or cooling processes; however, the correlation between the heat treatment, the phase structure, and the physical properties is still a controversy. Herein, three different phases are realized for Ag2TexS1-x (0.35 ≤ x ≤ 0.65) samples during the heat treatment, including the low-temperature crystalline phase, amorphous phase, and high-temperature cubic phase. The metastable amorphous phase is an intermediate phase formed during transition from the high-temperature cubic phase to the low-temperature crystalline phase upon cooling via a solid-state conversion rather than the conventional liquid quenching process. The relative content of these three phases is highly sensitive to the heat treatment process. This as-formed low-temperature crystalline phase, amorphous phase, and high-temperature cubic phase convert into the low-temperature crystalline phase and high-temperature cubic phase through long-time dwelling at the temperature below or above the transition temperature around 567 K, respectively. The status of the low-temperature crystalline phase, amorphous phase, and high-temperature cubic phase significantly affects the thermoelectric properties, resulting in the thermal hysteresis of thermoelectric properties. Below the phase transition temperature (TM), the electrical conductivity of the amorphous phase surpasses that of the low-temperature crystalline phase, which shows a growth of 112% for the Ag2Te0.60S0.40 sample annealed at 823 K in comparison with that of the sample annealed at 473 K. For Ag2Te0.50S0.50 samples annealed at 473 K, the maximum ZT value reaches 1.02 at 623 K during the initial test, while the maximum ZT value is improved to 1.34 at 523 K in the second-round test.

Optimization of Mechanical and Thermoelectric Properties of SnTe-Based Semiconductors by Mn Alloying Modulated Precipitation Evolution.

Multiscale defects engineering offers a promising strategy for synergistically enhancing the thermoelectric and mechanical properties of thermoelectric semiconductors. However, the specific impact of individual defects, in particular precipitation, on mechanical properties remains ambiguous. In this work, the mechanical and thermoelectric properties of Sn1.03- x Mnx Te (x = 0-0.30) semiconductors are systematically studied. Mn-alloying induces dense dislocations and Mn nano-precipitates, resulting in an enhanced compressive strength with x increased to 0.15. Quantitative calculations are performed to assess the strengthening contributions including grain boundary, solid solution, dislocation, and precipitation strengthening. Due to the dominant contribution of precipitation strengthening, the yield strength of the x = 0.10 sample is improved by ≈74.5% in comparison to the Mn-free Sn1.03 Te. For x ≥ 0.15, numerous MnTe precipitates lead to a synergistic enhancement of strength-ductility. In addition, multiscale defects induced by Mn alloying can scatter phonons over a wide frequency spectrum. The peak figure of merit ZT of ≈1.3 and an ultralow lattice thermal conductivity of ≈0.35 Wm-1  K-1 are obtained at 873 K for x = 0.10 and x = 0.30 samples respectively. This work reveals tha precipitation evolution optimizes the mechanical and thermoelectric properties of Sn1.03- x Mnx Te semiconductors, which may hold potential implications for other thermoelectric systems.

Strain-Induced Defect Evolution for the Construction of Porous Cu2-xSe with Enhanced Thermoelectric Performance.

Superionic Cu2-xSe, with disordered and even liquid-like Cu ions, has been extensively studied as a high efficiency thermoelectric material. However, the relationship between lattice stability and microstructure evolution in Cu2-xSe under strain, which is crucial for its application, has seldom been explored in previous research. In this study, we investigate the impacts of hydrostatic compression strain on the microstructural evolution and, consequently, its implications for thermoelectric performance. Molecular dynamics (MD) simulations show that high hydrostatic compression strain could induce local diffusion of Cu ions and Se twin evolution, resulting in the breaking and reforming of Cu-Se dynamic bonds and the unstable Se sublattice. The subsequent annealing process of the destabilized structure promoted Se evaporation from the sublattice and resulted in lotus-seedpod-like pores. The reduced sound velocity and intensified phonon scattering, due to pores, lead to a reduction in the lattice thermal conductivity from 0.44 W m-1 K-1 to 0.24 W m-1 K-1 at 800 K, a decrease of approximately 45%, in the porous Cu1.92Se sample. These findings reveal the relationship between stability and defect evolution in Cu2-xSe under high hydrostatic compression, offering a straightforward strategy of defect engineering for designing unique microstructures by leveraging the instability in superionic conductor materials.

Exploring the Epitaxial Growth Kinetics and Anomalous Hall Effect in Magnetic Topological Insulator MnBi2Te4 Films.

The discovery of MnBi2Te4-based intrinsic magnetic topological insulators has fueled tremendous interest in condensed matter physics, owing to their potential as an ideal platform for exploring the quantum anomalous Hall effect and other magnetism-topology interactions. However, the fabrication of single-phase MnBi2Te4 films remains a common challenge in the research field. Herein, we present an effective and simple approach for fabricating high-quality, near-stoichiometric MnBi2Te4 films by directly matching the growth rates of intermediate Bi2Te3 and MnTe. Through systematic experimental studies and thermodynamic calculations, we demonstrate that binary phases of Bi2Te3 and MnTe are easily formed during film growth, and the reaction of Bi2Te3 + MnTe → MnBi2Te4 represents the rate-limiting step among all possible reaction paths, which could result in the presence of Bi2Te3 and MnTe impurity phases in the grown MnBi2Te4 films. Moreover, Bi2Te3 and MnTe impurities introduce negative and positive anomalous Hall (AH) components, respectively, in the AH signals of MnBi2Te4 films. Our work suggests that further manipulation of growth parameters should be the essential route for fabricating phase-pure MnBi2Te4 films.

Realizing Excellent Structural and Thermoelectric Performance in Mg3Sb2-Based Alloys by Manipulating Mg Intrinsic Migration Kinetics with Interstitial Ni Doping.

N-type Mg3Sb2 is attracting increasing focus for its outstanding room-temperature (RT) thermoelectric (TE) performance; however, achieving reliable n-type conduction remains challenging due to negatively charged Mg vacancies. Doping with compensation charges is generally used but does not fundamentally resolve the high intrinsic activity and easy formation of Mg vacancies. Herein, a robust structural and thermoelectric performance is obtained by manipulating Mg intrinsic migration activity by precisely incorporating Ni at the interstitial site. Density functional theory (DFT) indicates that a strong performance originates from a significant thermodynamic preference for Ni occupying the interstitial site across the complete Mg-poor to -rich window, which dramatically promotes the Mg migration barrier and kinetically immobilizes Mg. As a result, the detrimental vacancy-associated ionized scattering is eliminated with a leading room-temperature ZT up to 0.85. This work reveals that interstitial occupation in Mg3Sb2-based materials is a novel approach promoting both structural and thermoelectric performance.

Enhanced Contact Performance and Thermal Tolerance of Ni/Bi2Te3 Joints for Bi2Te3-Based Thermoelectric Devices.

Ni metal has been widely used as a barrier layer in Bi2Te3-based thermoelectric devices, which establishes stable joints to link Bi2Te3-based legs and electrodes. However, the Ni/Bi2Te3 joints become very fragile when the devices were exposed to high temperature, causing severe performance deterioration and even device failure. Herein, stable Ni/Bi2Te3 joints have been established by arc spraying of the Ni barrier layer on the Bi2Te3-based alloys. The interface microstructure and contact performance including the bonding strength and contact resistivity of the arc-sprayed Ni/Bi2Te3 joints are investigated. The results indicate that, as compared with traditional Ni/Bi2Te3 joints, the arc-sprayed Ni/Bi2Te3 joints have comparably low contact resistivity while possessing a 50% higher bonding strength. Aging the joints as an exposure to high-temperature circumstances, the arc-sprayed Ni/Bi2Te3 joints exhibit much better tolerance to the thermal shock with stable bonding strength and contact resistivity. The enhanced interfacial contact performance and thermal tolerance should be attributed to the thick Ni barrier layer and interface reaction layer with good Ohmic contact. This work provides an effective strategy to establish stable joints for the Bi2Te3-based thermoelectric devices with improved thermal stability.

Synergetic Enhancement of Strength-Ductility and Thermoelectric Properties of Ag2 Te by Domain Boundaries.

Simultaneously improving the mechanical and thermoelectric (TE) properties is significant for the engineering applications of inorganic TE materials. In this work, a novel nanodomain strategy is developed for Ag2 Te compounds to yield 40% and 200% improved compressive strength (160 MPa) and fracture strain (16%) when compared to domain-free samples (115 MPa and 5.5%, respectively). The domained samples also achieve a 45% improvement in average ZT value. The domain boundaries (DBs) provide extra sites for dislocation nucleation while pinning the dislocation movement, resulting in superior strength and ductility. In addition, phonon scattering induced by DBs suppresses the lattice thermal conductivity of Ag2 Te and also reduces the weighted mobility. These findings provide new insights into grain and DB engineering for high-performance inorganic semiconductors with robust mechanical properties.

Manipulating the Interfacial Band Bending For Enhancing the Thermoelectric Properties of 1T'-MoTe2 /Bi2 Te3 Superlattice Films.

Interfacial charge effects, such as band bending, modulation doping, and energy filtering, are critical for improving electronic transport properties of superlattice films. However, effectively manipulating interfacial band bending has proven challenging in previous studies. In this study, (1T'-MoTe2 )x (Bi2 Te3 )y superlattice films with symmetry-mismatch were successfully fabricated via the molecular beam epitaxy. This enables to manipulate the interfacial band bending, thereby optimizing the corresponding thermoelectric performance. These results demonstrate that the increase of Te/Bi flux ratio (R) effectively tailored interfacial band bending, resulting in a reduction of the interfacial electric potential from ≈127 meV at R = 16 to ≈73 meV at R = 8. It is further verified that a smaller interfacial electric potential is more beneficial for optimizing the electronic transport properties of (1T'-MoTe2 )x (Bi2 Te3 )y . Especially, the (1T'-MoTe2 )1 (Bi2 Te3 )12 superlattice film displays the highest thermoelectric power factor of 2.72 mW m-1 K-2 among all films, due to the synergy of modulation doping, energy filtering, and the manipulation of band bending. Moreover, the lattice thermal conductivity of the superlattice films is significantly reduced. This work provides valuable guidance to manipulate the interfacial band bending and further enhance the thermoelectric performances of superlattice films.

The roles of ubiquitin-proteasome system and regulator of G protein signaling 4 in behavioral sensitization induced by a single morphine exposure.

AIMS: Opioid addiction is a major public health issue, yet its underlying mechanism is still unknown. The aim of this study was to explore the roles of ubiquitin-proteasome system (UPS) and regulator of G protein signaling 4 (RGS4) in morphine-induced behavioral sensitization, a well-recognized animal model of opioid addiction. METHODS: We explored the characteristics of RGS4 protein expression and polyubiquitination in the development of behavioral sensitization induced by a single morphine exposure in rats, and the effect of a selective proteasome inhibitor, lactacystin (LAC), on behavioral sensitization. RESULTS: Polyubiquitination expression was increased in time-dependent and dose-related fashions during the development of behavioral sensitization, while RGS4 protein expression was not significantly changed during this phase. Stereotaxic administration of LAC into nucleus accumbens (NAc) core inhibited the establishment of behavioral sensitization. CONCLUSION: UPS in NAc core is positively involved in behavioral sensitization induced by a single morphine exposure in rats. Polyubiquitination was observed during the development phase of behavioral sensitization, while RGS4 protein expression was not significantly changed, indicating that other members of RGS family might be substrate proteins in UPS-mediated behavioral sensitization.

Direct observation of cation diffusion driven surface reconstruction at van der Waals gaps.

Weak interlayer van der Waals (vdW) bonding has significant impact on the surface/interface structure, electronic properties, and transport properties of vdW layered materials. Unraveling the complex atomistic dynamics and structural evolution at vdW surfaces is therefore critical for the design and synthesis of the next-generation vdW layered materials. Here, we show that Ge/Bi cation diffusion along the vdW gap in layered GeBi2Te4 (GBT) can be directly observed using in situ heating scanning transmission electron microscopy (STEM). The cation concentration variation during diffusion was correlated with the local Te6 octahedron distortion based on a quantitative analysis of the atomic column intensity and position in time-elapsed STEM images. The in-plane cation diffusion leads to out-of-plane surface etching through complex structural evolutions involving the formation and propagation of a non-centrosymmetric GeTe2 triple layer surface reconstruction on fresh vdW surfaces, and GBT subsurface reconstruction from a septuple layer to a quintuple layer. Our results provide atomistic insight into the cation diffusion and surface reconstruction in vdW layered materials.

"Cluster Bomb" Based Bismuth Nano-in-Micro Spheres Formed Dry Powder Inhalation for Thermo-Radio Sensitization Effects of Lung Metastatic Breast Cancer.

Lung metastatic breast cancer (LMBC) is mainly diagnosed through CT imaging and radiotherapy could be the most common method in the clinic to inhibit tumor proliferation. While the sensitivity of radiotherapy is always limited due to the hypoxic tumor microenvironment and high doses of irradiation easily induce systemic cytotoxicity. Metal-based materials applied as radiosensitizers have been widely investigated to improve efficiency and reduce the doses of irradiation. Herein, it is aimed to overcome these problems by designing biodegradable lipid-camouflaged bismuth-based nanoflowers (DP-BNFs) as both a photo-thermo-radiosensitizer to develop a novel photothermal therapy (PTT) and radiotherapy combination strategy for LMBC treatment. To achieve effective lung deposition, "Cluster Bomb" structure-based DP-BNFs nano-in-micro dry powder inhalation (DP-BNF@Lat-MPs) are formulated through spray-dried technology. The DP-BNFs "cluster" in the microsphere to improve their tumor-targeted lung deposition with a high fine particle fraction followed by burst releasing of DP-BNFs for targeting delivery and LMBC therapy. The DP-BNF@Lat-MPs exhibit excellent photothermal conversion efficiency, radiotherapy enhancement, and CT imaging ability in vitro, which synergistically inhibit cell proliferation and metastasis. In vitro and in vivo data prove that combining PTT and radiotherapy with DP-BNF@Lat-MPs as a thermo-radio dual-sensitizer significantly enhances LMBC tumor metastasis inhibition with good biocompatibility and low toxicity.

Tuning Thermoelectric Conversion Performance of BiSbTe/Epoxy Flexible Films with Dot Magnetic Arrays.

Embedding of magnetic functional units into the thermoelectric (TE) materials has been demonstrated to be an effective way to enhance the TE conversion performance. However, the magnetic functional units in TE materials are all randomly distributed. In this paper, to explore the effect of the ordering of the magnetic functional units on TE conversion performance, a series of BiSbTe/epoxy flexible thermoelectromagnetic (TEM) films with dot magnetic arrays were successfully prepared by a two-step screen printing combined with a hot pressing process. TEM films with dot magnetic arrays can achieve high carrier mobility, while the carrier concentration increases due to large coercivity. Therefore, its electrical conductivities are significantly improved on the condition that it maintains a high Seebeck coefficient. The TEM film with hexagonal-dot magnetic arrays exhibits the best electrical transport properties, for which the room-temperature power factor reaches 1.51 mW·m-1·K-2, increased by 33.6 and 36.1% as compared with those of the pristine TE film and the TEM film with a continuous magnetic layer, respectively. This work provides a new way to enhance the TE conversion performance of flexible TEM films through the ordered magnetic arrays.

Effectiveness and Biomechanical Analysis of the Ortho-Bridge System on Femoral Fracture Healing: A Retrospective Analysis.

Background: Among the surgical methods for femoral fractures, the Ortho-Bridge System (OBS) appears to heal fractures via an uncommon process. We compared its effectiveness and biomechanical aspects to those of a locking compression plate (LCP) and explained the healing process demonstrated by the OBS. Methods: Eleven femoral shaft fracture cases treated with OBS between July 2017 and May 2020 were retrospectively reviewed. Clinical and radiographic data were collected during regular postoperative follow-up visits and assessed via the Harris Hip Score and Knee Society Score. We performed biomechanical experiments of OBS. We simulated different fracture conditions and selected appropriate screw holes at the fracture's far and near segments. The OBS module was placed according to the position of LCP's locking hole at both ends of the fracture; then, a static three-point bending test was performed. Results: All patients had contralateral callus growth with secondary fracture healing. Healing time was 3-5 months with excellent hip and knee function. When the key screw distance was 22-34 mm, the OBS was significantly less stiff than the LCP (P < 0.05). The stiffness of LCP and OBS decreased significantly when the key screw distance was 49-82 mm, with the LCP being slightly stronger (P < 0.05). Conclusions: Femoral shaft fracture treatment with OBS demonstrated secondary healing. When the distance between the key screws was 20-40 mm, the elasticity was higher in OBS than in LCP, possibly producing axial micro-motion to stimulate callus formation and promote fracture healing, which differ from the plate's primary healing process.

High Transverse Thermoelectric Performance and Interfacial Stability of Co/Bi0.5Sb1.5Te3 Artificially Tilted Multilayer Thermoelectric Devices.

Artificially tilted multilayer thermoelectric devices (ATMTDs) have attracted extensive attention because of their numerous advantages, such as high integration, great structural freedom, and large transverse Seebeck coefficients. ATMTDs are composed of numerous alternating stackings of two types of materials with large differences in electrical and thermal transport. Therefore, it is of great interest to find ATMTDs with both high transverse thermoelectric performance and good interfacial stability to develop their practical application. In this work, cobalt (Co) and Bi0.5Sb1.5Te3 (BST) are chosen to prepare Co/BST ATMTDs. The interfacial structure and composition of Co/BST are characterized, and its interfacial stability and transverse thermoelectric performance are evaluated. The results show that the thickness of the Co/BST interfacial reaction layer is about 4 µm. Annealing at 473 K for 32 h does not increase the thickness, which indicates better interfacial stability than Ni/BST. After structure optimization, Co/BST ATMTD has ZTzx = 0.41, which is second only to YbAl3/BST ATMTDs. Meanwhile, the transverse Seebeck coefficient reaches -120.38 µV/K. The outstanding interfacial stability and transverse thermoelectric performance promise excellent thermal response and refrigeration performance with Co/BST ATMTDs.

Lipid-coated bismuth nanoflower as the thermos-radio sensiti for therapy of lung metastatic breast cancer: Preparation, optimisation, and characterisation.

Lung metastatic breast cancer (LMBC) leads to a large number of deaths in women with breast cancer, and radiotherapy has been considered the common assay for tumour therapy except for surgery. However, radiotherapy still faces problems of low efficiency due to resistance and easily induced side effects. Here, the authors designed lipid-decorated bismuth-based nanoflowers (DP-BNFs) as both a radiosensitiser and a photothermal therapy agent for LMBC treatment. The BNFs were prepared by oxidation of bismuth nitrate and subsequent reduction using sodium borohydride. The preparation parameters and formulation of DP-BNFs were optimised via a single-factor experiment, with the factors including reaction temperature, a molar ratio of reducing agents, and the types and amount of decorated lipid materials. The result indicated that the BNFs prepared at 170°C with the Bi/NaBH4 ratio of 1:0.7 exhibited the best yield and particle size around 160 nm. After being spray dried with lactose to prepare dry powder inhalation (DP-BNF@Lat-MPs), their effects on improving therapeutic efficiency of the radiotherapy and photothermal therapy combination were measured using the western blot assay to determine the tumour apoptosis. In a word, DP-BNF@Lat-MPs could be a novel inhalable integrated microsphere that provides a new possibility for thermoradiotherapy of LMBC.

High-Performance Thermoelectric α-Ag9 Ga1-x Te6 Compounds with Ultralow Lattice Thermal Conductivity Originating from Ag9 Te2 Motifs.

We have determined the complex atomic structure of high-temperature α-Ag9 GaTe6 phase with a hexagonal lattice (P63 mc space group, a=b=8.2766 Å, c=13.4349 Å). The structure has outer [GaTe4 ]5- tetrahedrons and inner [Ag9 Te2 ]5+ clusters. All of the Ag ions are disorderly distributed in the lattice. Seven types of the Ag atoms constitute the cage-like [Ag9 Te2 ]5+ clusters. The highly disordered Ag ions vibrate in-harmonically, producing strong coupling between low frequency optical phonons and acoustic phonons. This in conjunction with a low sound velocity of 1354 m s-1 leads to an ultralow thermal conductivity of 0.20 W m-1 K-1 at 673 K. Meanwhile, the deficiency of Ga in Ag9 Ga1-x Te6 compounds effectively optimizes the electronic transport properties. Ag9 Ga0.91 Te6 attains a highest power factor of 0.40 mW m-1 K-2 at 673 K. All these contribute to a much-improved ZT value of 1.13 at 623 K for Ag9 Ga0.95 Te6 , which is 41 % higher than that of the pristine Ag9 GaTe6 sample.