Search

In this study, CoCrFeNiV non-equiatomic high entropy alloys (HEAs) with varying N content were prepared using vacuum hot-press sintering. The effects of N content on the alloy's microstructure, mechanical properties, and tribological behavior at different temperatures were investigated. The results indicate that the N-added alloys primarily maintain an FCC phase. With increasing N content, the σ phase in the alloy gradually decreases, while the VN content increases, leading to grain refinement. This results in a 10.7 % increase in hardness, a 9 % increase in compression strength, and a 56 % increase in compression deformation. Below 400 °C, the primary wear mechanisms are adhesive wear, spalling wear, and slight oxidative wear, while above 600 °C, oxidative wear dominates. The addition of N reduced the wear rates of the alloy by 33.8 %, 8.1 %, and 31.3 % at RT, 200 °C, and 600 °C, respectively, and decreases the coefficient of friction at all temperatures. In summary, N addition improves the alloy's tribological performance at various temperatures. [ABSTRACT FROM AUTHOR]

Mosaic-crystal microstructure is one of the optimal strategies for decoupling and balancing thermal and electrical transport properties in thermoelectric materials. Herein, we successfully achieve the desired nanoscale mosaic structures in triple-component Cu 2−y S 1/3 Se 1/3 Te 1/3 solid solutions using Cu 2 S, Cu 2 Se, and Cu 2 Te matrix compounds. They are solved in hexagonal structures with space group R 3 ̅ m by means of single crystal structural solution and Rietveld refinement. Electron backscatter diffraction measurements show that all the samples are polycrystalline compounds with the grain size in the range of micrometers. However, transmission electron microscopic study reveals that these microscale grains are quasi-single crystals consist of a variety of 10–30 nm mosaic grains. Each mosaic grain is a perfect crystal but titled or rotated with respect to others by a very small angle. In this case, excellent electrical transports are maintained but exceptional low thermal conductivity is achieved throughout the whole temperature range, which is attributed to the combined phonon scatterings by point defects, liquid-like copper ions, and lattice strains or interfaces of mosaic nanograins. Combining all these favorable factors, remarkably high thermoelectric performance is achieved in Cu 1.98 S 1/3 Se 1/3 Te 1/3 with a maximum zT of 1.9 at 1000 K. [ABSTRACT FROM AUTHOR]

Abstract: Filling two or multiple atoms into the cages of a skutterudite crystal is a successful way to enhance the thermoelectric figure of merit in n-type partially filled skutterudites. Here we use La–Yb double filling to improve the thermoelectric performance of p-type skutterudites Yb x La y Fe2.7Co1.3Sb12 (x + y = 0.85, x = 0, 0.09, 0.17, 0.25, 0.34, 0.42, 0.85). The samples are synthesized by directly melting the raw materials followed by a long time annealing process. X-ray diffraction measurement confirms the skutterudite structure of the samples. By increasing the filling fraction of Yb, the lattice thermal conductivity is gradually depressed and reaches the lowest value of 0.9 W m−1 K−1 at high temperatures. At the same time, the Seebeck coefficient decreases while the electrical conductivity increases. The maximum power factor around 27 μW cm−1 K−2 for samples Yb0.17La0.68Fe2.7Co1.3Sb12 and Yb0.25La0.60Fe2.7Co1.3Sb12 is achieved at 600 K and 700 K, respectively. Sample Yb0.25La0.60Fe2.7Co1.3Sb12 has the maximum thermoelectric figure of merit 0.99 at 700 K, which is among the highest values among p-type filled skutterudites. [Copyright &y& Elsevier]

Aquatic ecosystems and drinking water supply systems worldwide are increasingly affected by taste and odor episodes. In this study, molecular approaches including next-generation sequencing (NGS) and quantitative polymerase chain reaction (qPCR) were used to study the diversity and dynamics of cyanobacteria and 2-methylisoborneol (2-MIB)-producing cyanobacteria in Yuqiao Reservoir, a eutrophicated drinking water reservoir in Tianjin city, northern China. NGS revealed that the entire cyanobacterial community consisted of 16 genera, with Planktothrix (28.8%), Pseudanabaena (18.4%), Cylindrospermosis (7.8%), and Microcystis (7.6%) being the dominant genera, while microscopic examination identified only eight cyanobacterial genera. NGS of the 2-MIB synthesis gene revealed that Pseudanabaena and Planktothricoides were the main 2-MIB producers, with Pseudanabaena being dominant. This finding demonstrated that NGS can identify 2-MIB producers quickly and accurately and it can thus play an important role in the practical monitoring of aquatic ecology. The qPCR test showed 2-MIB synthesis gene with 4.27 × 106 copies/L to 2.24 × 109copies/L occurring at the three sampling sites. The mic gene copy number increased before the 2-MIB concentration increased, indicating that forecasting role in dealing with the 2-MIB concentration by gene copy number. Predicting 2-MIB by qPCR in the field must be verified with additional studies. The combination of NGS and qPCR can be an even more comprehensive method to provide early warning information to managers of reservoirs and water utilities facing taste and odor incidents. This is the first amplicon NGS dataset based on 2-MIB gene to study the diversity and dynamics of 2-MIB-producing cyanobacteria. [Display omitted] • Diversity of 2-MIB-producing cyanobacteria by next-generation sequencing. • qPCR can predict 2-MIB production in advance. • Next-generation sequencing makes up for lack of microscopic examination. [ABSTRACT FROM AUTHOR]

Soil microorganisms play an essential role in the redistribution of soil aggregate sizes due to the microenvironmental changes. Yet, little is known regarding how individual microbial taxa within different-sized aggregates respond to agronomic practice. This study integrated physical, chemical, and molecular techniques (i.e., high-throughput DNA sequencing and qPCR) to assess the influence of corn-tobacco rotation on the soil microbial community at the soil microenvironment scale, i.e., within mega- (>2 mm), macro- (0.25–2 mm) and micro-aggregate (<0.25 mm) fractions. The soil samples (0–20 cm) analyzed in this study originated from corn and tobacco, which were cultivated under three different fertilization regimes. The results demonstrate that corn-tobacco rotation substantially impacted the distribution of aggregate sizes, and the shift in soil microbial communities associated with soil aggregates was related to changes in soil total carbon (TC), the C/N ratio and pH. The indicator microbial taxa (i.e., those were sensitive to crop rotation) varied with aggregate size. When compared with tobacco soil, the corn soil showed higher relative abundances of probably more copiotrophic taxa across large-sized aggregates, also with more bacteria in mega-aggregates and more fungi in macro-aggregates. Changes in total microbial communities associated with mega- and macro-aggregates in response to crop rotation were driven mainly by alterations in bacterial and fungal communities, respectively. Overall, the results of this study demonstrate that soil aggregate size strongly affected the microbial community composition on agricultural fields, promoting the differential responses between bacteria and fungi to crop rotation in specific size of aggregates. [ABSTRACT FROM AUTHOR]

Recently, many novel superionic thermoelectric materials have been discovered along the concept of “phonon-liquid electron-crystal” (PLEC). Among them, Cu 2- x Se-based liquid-like materials are typical examples. In this study, a series of copper-deficient Cu 2- x Se (0.05 ≤ x ≤ 0.25) materials were synthesized and used to study the role of Cu vacancies on the electrical and thermal transport properties. The X-ray photoelectron spectroscopy (XPS) measurements suggest that the valence states of Cu and Se are independent on the Cu/Se atomic ratio. With increasing the content of Cu vacancies, the hole concentration is monotonously increased, leading to the improved electrical conductivity and reduced Seebeck coefficient. Based on the single parabolic band model analysis, it is found that changing the content of Cu vacancies does not obviously modify the material's electronic band structure and effective mass. Due to the presence of highly mobile Cu ions inside the crystal structure, the lattice thermal conductivities of all Cu 2- x Se (0.05 ≤ x ≤ 0.25) materials are very low with values around 0.39 W m −1 K −1 at 500 K. Because of the significantly reduced Seebeck coefficient and increased electronic thermal conductivity, the thermoelectric figure of merit zTs are decreased when increasing x from 0.05 to 0.25. At 750 K, a maximum zT of 0.46 is obtained in Cu 1.95 Se among all Cu 2- x Se (0.05 ≤ x ≤ 0.25) materials. [ABSTRACT FROM AUTHOR]

Short carbon fiber-reinforced p-type skutterudite CeFe 4 Sb 12 composites were fabricated by a melting-annealing process combined with spark plasma sintering, the effect of carbon fibers on the thermoelectric and mechanical properties were investigated, and the relationship between the microstructure and the mechanical properties of the composites were elucidated. The results indicate that the carbon fibers were well distributed throughout the matrix and were in intimate contact with the CeFe 4 Sb 12 grains without interlayers. Both the flexural strength and the fracture toughness of CeFe 4 Sb 12 were enhanced with the addition of the carbon fibers. Considering the tradeoff between the thermoelectric and mechanical properties, the optimal carbon fiber content was found to be 1 vol.%. The flexural strength of the composite containing 1 vol.% fiber was improved by 53%, whereas the fracture toughness and ZT value remained nearly unchanged. [ABSTRACT FROM AUTHOR]

The development of a rapid-forming in-situ sprayable hydrogel with the functions of tumor treatment and wound healing is essential for eliminating residual tumor tissue and promoting wound healing caused by surgical resection. On account of its semiconductor properties, β-FeSi 2 (FS) was widely explored as a thermoelectric material. In this work, FS was first applied as a bioactive material for the application of tissue engineering. Excitedly, we found that FS could be used as a novel antitumor agent. It exhibited excellent photothermal performance, and the released Fe ions could generate •OH under the acidic conditions and excessive H 2 O 2 in the tumor microenvironment. Moreover, the sprayable β-FeSi 2 -incorporated sodium alginate (FS/SA) hydrogel was prepared as an instant gelation after spraying in situ , contributing to timely tumor-induced skin wound healing and efficiently suppressing tumors through photothermal and chemodynamic therapy (PTT and CDT). Furthermore, the released bioactive Fe and Si ions could promote the migration and differentiation of endothelial cells and the pro-angiogenesis of skin wounds. Accordingly, such sprayable hydrogel played an effective role in emergency wound treatment with the advantage of convenience and portability. Overall, with incorporation of FS into the sprayable FS/SA hydrogel, the composite hydrogel possessed dual functions of tumor therapy and skin wound healing. [ABSTRACT FROM AUTHOR]

Achieving large Fermi energy splitting under illumination is critical for improving the performance of the photovoltaic devices. We conducted the energy band structure modulation of MoS 2 thin films to realize its photovoltaic operation on n-type c-Si and improve the photovoltaic performance of the formed MoS 2 /n-Si heterojunction solar cells. By capping with a MoO x overlayer, there is electrons orientation flowing from the valence band of MoS 2 into the O-deficiency states of MoO x due to their energy level overlap, which leads to the Fermi level downshift of the MoS 2 films and consequently its conductive type conversion. After the MoS 2 layer doped, we found that the built-in electric field of the fabricated MoS 2 /n-Si heterojunction devices greatly improved owing to the larger hetero-interface Fermi level differences. And, the defects recombination losses at the hetero-interface also reduced because of the holes selectively extracting effect of the O-vacencies in MoO x. As a result, the photo-generated carriers separation and extraction are both enhanced at the hetero-interface, so that the MoS 2 /n-Si devices exhibited excellent photovoltaic performance under the modulation doping effect. The conclusive power conversion efficiency of the doped MoS 2 /n-Si solar cells is of 5.47% with respectively optimized electrical parameters (V oc of 289 mV, FF of 60.72 and J sc of 31.25 mA/cm2). This observation of MoO x modulation doping effect on large-area sputtering MoS 2 could help in building a more appropriate interface carrier transport mechanism in photovoltaic and optoelectronic device applications of 2D materials. • The PV application of semiconducting MoS 2 on n-type c-Si is realized. • The energy band structure of MoS 2 is modulated by MoO x doping scheme. • Doping mechanism lies on carriers contact transfer due to energy band overlap. • Interface carriers transport efficiently enhanced by larger Fermi level splitting. • The PV performance of MoS 2 /n-Si devices improved significantly with MoO x doping. Achieving large Fermi energy splitting under illumination is critical for improving the performance of photovoltaic devices. In this work, we conducted the energy band structure modulation of MoS 2 thin films via MoO x doping scheme to realize its photovoltaic operation on n-type c-Si by magnetron sputtering. It is found that, by capping a MoO x overlayer, the MoS 2 electrons density decreased and the Fermi level shifted ~0.4 eV towards valence band, consequently the MoS 2 conductive type changing. With this doped MoS 2 layer, the built-in electric field of fabricated MoS 2 /n-Si heterojunction devices greatly improved and exceeded 400 mV owing to the larger interface energy-level differences. Meanwhile, the defects recombination losses reduced benefiting from the holes-selective behavior of O-deficiencies in MoO x , so that the photo-generated carriers extraction process were promoted. As a result, the doped MoS 2 /n-Si devices showed excellent rectification behavior with rectifying ratio to 105 and ideality of 1.12. The TRPL spectrums corroborated the enhanced carrier transport mechanism at MoS 2 /n-Si interface by MoO x modulation doping effect. Correspondingly, the significant improvement of doped MoS 2 /n-Si solar cells performance (V oc of 289 mV, FF of 60.72% and J sc of 31.25 mA/cm2) was achieved, exhibiting an optimized conversion efficiency of 5.47%. The UPS analysis revealed that the doping mechanism of MoO x /MoS 2 stacks lies in energy band overlap and electrons contact transfer between these two materials. This observation of MoO x modulation doping effect on large-area sputtering MoS 2 could help in building a better interface carrier transport in photovoltaic and optoelectronic applications of 2D materials. [ABSTRACT FROM AUTHOR]

Thermoelectric materials require not only high performance to maximize the energy conversion efficiency but also good mechanical properties to guarantee machinability and reliable operation. It is usually hard to embrace both at once. Herein, we demonstrated the entropy engineering as a promising avenue to realize both exceptional thermoelectric performance and robust mechanical properties in multicomponent alloys Cu 2- y Ag y Te 1-2 x S x Se x. Entropy engineering by mixing multiple elements stabilizes the high-symmetry hexagonal structure, extends the solubility limit of Ag, and concurrently lessens the phase transition numbers. Furthermore, with co-alloying of S/Se and Ag in Cu 2 Te, the carrier concentration is largely reduced while the effective mass is enhanced, yielding higher Seebeck coefficient and power factor. Owing to the strong phonon scattering by lattice disorder, the thermal conductivity is decreased by one order of magnitude, reaching 0.29 W m−1 K−1 at room temperature, which is even lower than the amorphous limit. A state-of-the-art peak zT of 1.4 and average zT of 0.74 are achieved in Cu 1.9 Ag 0.1 Te 0.6 S 0.2 Se 0.2. Moreover, the mechanical properties are significantly improved in virtue of the entropy engineering strengthening effect, making it more promising for thermoelectric applications. Record-high average zT of 0.74 and remarkably improved compressive strength were achieved in multicomponent alloys Cu 2- y Ag y Te 1-2 x S x Se x through entropy engineering [Display omitted]. [ABSTRACT FROM AUTHOR]