High anisotropy in electrical and thermal conductivity through the design of aerogel-like superlattice (NaOH)0.5NbSe2.

Interlayer decoupling plays an essential role in realizing unprecedented properties in atomically thin materials, but it remains relatively unexplored in the bulk. It is unclear how to realize a large crystal that behaves as its monolayer counterpart by artificial manipulation. Here, we construct a superlattice consisting of alternating layers of NbSe2 and highly porous hydroxide, as a proof of principle for realizing interlayer decoupling in bulk materials. In (NaOH)0.5NbSe2, the electric decoupling is manifested by an ideal 1D insulating state along the interlayer direction. Vibration decoupling is demonstrated through the absence of interlayer models in the Raman spectrum, dominant local modes in heat capacity, low interlayer coupling energy and out-of-plane thermal conductivity (0.28 W/mK at RT) that are reduced to a few percent of NbSe2's. Consequently, a drastic enhancement of CDW transition temperature (>110 K) and Pauling-breaking 2D superconductivity is observed, suggesting that the bulk crystal behaves similarly to an exfoliated NbSe2 monolayer. Our findings provide a route to achieve intrinsic 2D properties on a large-scale without exfoliation.

Improved figure of merit (z) at low temperatures for superior thermoelectric cooling in Mg3(Bi,Sb)2.

The low-temperature thermoelectric performance of Bi-rich n-type Mg3(Bi,Sb)2 was limited by the electron transport scattering at grain boundaries, while removing grain boundaries and bulk crystal growth of Mg-based Zintl phases are challenging due to the volatilities of elemental reactants and their severe corrosions to crucibles at elevated temperatures. Herein, for the first time, we reported a facile growth of coarse-grained Mg3Bi2-xSbx crystals with an average grain size of ~800 µm, leading to a high carrier mobility of 210 cm2 · V-1 · s-1 and a high z of 2.9 × 10-3 K-1 at 300 K. A [Formula: see text]T of 68 K at Th of 300 K, and a power generation efficiency of 5.8% below 450 K have been demonstrated for Mg3Bi1.5Sb0.5- and Mg3Bi1.25Sb0.75-based thermoelectric modules, respectively, which represent the cutting-edge advances in the near-room temperature thermoelectrics. In addition, the developed grain growth approach can be potentially extended to broad Zintl phases and other Mg-based alloys and compounds.

A quasi-one-dimensional bulk thermoelectrics with high performance near room temperature.

Pursuing efficient thermoelectricity from low-dimensional materials has been highly motivated since the seminal work of Hicks and Dresselhaus. In fact, many superior thermoelectric materials like Bi2Te3, Mg3Sb2/Mg3Bi2 and SnSe are quasi-two-dimensional (q2D), though the advantages of two-dimensionality appear to be diverse and sometimes controversial. Here, we report on a remarkably high thermoelectric performance in TlCu3Te2, which is quasi-one-dimensional (q1D) with a further reduced dimension. The thermoelectric figure of merit zT along its q1D axis amounts to 1.3 (1.5) at 300 (400) K, rivaling the best ever reported at these temperatures. The high thermoelectric performances benefit from, on one hand, large power factors derived from a center-hollowed, pancake-like Fermi pocket with q1D dispersion at the edge of a narrow band gap, and on the other hand, small lattice thermal conductivities caused by the large and anharmonic q1D lattice consisting of heavy, lone-pair-electron bearing (Tl+) and weakly-bonded (Cu+) ions. This compound represents the first bulk material with quasi-uniaxial thermoelectric transport of application level, offering a renewed opportunity to exploit reduced dimensionality for high-performance thermoelectricity.

Highly efficient thermoelectric air conditioner with kilowatt capacity realized by ground source heat-exchanging system.

The enormous need for refrigeration of modern human life has inevitably aggravated the environmental crisis worldwide. To date, there are very few refrigeration technologies available beholding both harmless refrigerants and high efficiency. Here, we proposed a geothermal-thermoelectric air conditioning system (GeoTEAC) with refrigerant-free and high energy efficiency through synergistically combining the merits of thermoelectric effect and ground source heat exchanging system. The system showed competitive cooling and heating COPs of 5.83 and 2.92, respectively, with kilowatt capacity, which are 3-4 times higher than that of previously reported thermoelectric air-conditioning setups. For a conceptual scenario, we demonstrated the lowest TEWI values for the GeoTEAC system among different air-conditioning types. Our work provides sustainable and climate-friendly solutions to realize worldwide emission peaks and carbon neutralization.

Ultralow thermal conductivity from transverse acoustic phonon suppression in distorted crystalline α-MgAgSb.

Low thermal conductivity is favorable for preserving the temperature gradient between the two ends of a thermoelectric material, in order to ensure continuous electron current generation. In high-performance thermoelectric materials, there are two main low thermal conductivity mechanisms: the phonon anharmonic in PbTe and SnSe, and phonon scattering resulting from the dynamic disorder in AgCrSe2 and CuCrSe2, which have been successfully revealed by inelastic neutron scattering. Using neutron scattering and ab initio calculations, we report here a mechanism of static local structure distortion combined with phonon-anharmonic-induced ultralow lattice thermal conductivity in α-MgAgSb. Since the transverse acoustic phonons are almost fully scattered by the compound's intrinsic distorted rocksalt sublattice, the heat is mainly transported by the longitudinal acoustic phonons. The ultralow thermal conductivity in α-MgAgSb is attributed to its atomic dynamics being altered by the structure distortion, which presents a possible microscopic route to enhance the performance of similar thermoelectric materials.

Spark Plasma Sintered Bulk Nanocomposites of Bi2Te2.7Se0.3 Nanoplates Incorporated Ni Nanoparticles with Enhanced Thermoelectric Performance.

Bi2Te3-based compounds are important near room temperature thermoelectric materials with commercial applications in thermoelectric modules. However, new routes leading to improved thermoelectric performance are highly desirable. Incorporation of superparamagnetic nanoparticles was recently proposed as a means to promote the thermoelectric properties of materials, but its feasibility has rarely been examined in mainstream thermoelectric materials. In this study, high quality single-crystalline Bi2Te2.7Se0.3 nanoplates and Ni nanoparticles were successfully synthesized by solvothermal and thermal decomposition methods, respectively. Bulk nanocomposites consisting of Bi2Te2.7Se0.3 nanoplates and superparamagnetic Ni nanoparticles were prepared by spark plasma sintering. It was found that incorporation of Ni nanoparticles simultaneously increased the carrier concentration and provided additional scattering centers, which resulted in enlarged electric conductivities and Seebeck coefficients. The greatly improved ZT was achieved due to the increase in power factor. Spark plasma sintered bulk nanocomposites of Bi2Te2.7Se0.3 nanoplates incorporated by 0.4 mol %Ni nanoparticles (in molar ratio) showed a figure-of-merit ZT of 0.66 at 425 K, equivalent to 43% increase when compared to pure Bi2Te2.7Se0.3 nanoplates. The results revealed that incorporation of magnetic nanoparticles could be an effective approach for promoting the thermoelectric performance of conventional semiconductors.

A graphene-based smart thermal conductive system regulated by a reversible pressure-induced mechanism.

Thermal dissipation and thermal insulation are important for maintaining the normal operation of devices, extending the service life of instruments, ensuring efficient energy utilization, and improving temperature-related human comfort. Yet it is difficult to achieve both the functions of thermal dissipation and thermal insulation in a single material with a specific thermal conductivity under specific conditions. In this work, based on the huge difference in thermal conductivity between air and reduced graphene oxide (rGO), a pressure-induced mechanism is used to regulate the amount of air inside an rGO foam, so that a periodic reversible change of thermal conductivity can be realized, achieving the dual functions of thermal dissipation and thermal insulation to meet the requirements of different application scenarios. Further fitting calculations suggest that the thermal conductivity of rGO foam is positively and negatively associated with the applied pressure and temperature, respectively, and it can be calculated for given pressure and temperature conditions. The pressure-induced reversible regulation of thermal conductivity in rGO foam provides a new design construct for smart thermal-management devices, and a new direction of application for 2D materials.

Enhanced thermoelectric properties in N-type Mg2Si0.4-x Sn0.6Sb x synthesized by alkaline earth metal reduction.

Mg2Si1-x Sn x -based compounds have been recognized as promising thermoelectric materials owing to their high figure-of-merit ZTs, abundance of raw constituent elements and nontoxicity. However, further improvement in the thermoelectric performance in this type of material is still constrained by the high thermal conductivity. In this work, we prepared a series of representative Mg2Si0.4-x Sn0.6Sb x (x = 0, 0.0075, 0.008, 0.009, 0.01, 0.011) samples via the alkaline earth metal reduction method through a combination of ball milling and spark plasma sintering (SPS) processes. The samples featured many dislocations at the grain boundaries and plenty of nanoscale-coherent Mg2Si-Mg2Sn spinodal phases; both of which can effectively scatter heat-carrying phonons and have nearly no impact on the carrier transport. Meanwhile, Sb-doping can efficiently optimize the carrier concentration and significantly suppress the bipolar effects. As a result, a maximal ZT of 1.42 at 723 K and engineering (ZT)eng of 0.7 are achieved at the optimal Sb-doping level of x = 0.01. This result indicates that the alkaline earth metal reduction method could be an effective route to engineer phonon transport and improve the thermoelectric performance in Mg2Si1-x Sn x -based materials.

Ultrastrong Boron Frameworks in ZrB12 : A Highway for Electron Conducting.

ZrB12 , with a high symmetrical cubic structure, possesses both high hardness ≈27.0 GPa and ultralow electrical resistivity ≈18 µΩ cm at room temperature. Both the superior conductivity and hardness of ZrB12 are associated with the extended BB 3D covalent bonding network as it is not only favorable for achieving high hardness, but also provides conducting channels for transporting electrons.

[Antimicrobial susceptibility of community-acquired respiratory tract pathogens isolated from class B hospitals in China during 2013 and 2014].

OBJECTIVE: To investigate the drug-resistance rate of community-acquired respiratory tract pathogens isolated from class B hospitals in China during 2013 and 2014. METHODS: A total of 860 strains (S.pneumoniae 299, K. pneumoniae 221, H. influenzae 185, S. aureus 116, and M. catarrhalis 39) of non-duplicated community-acquired respiratory tract pathogens were isolated from 10 class B hospitals in 9 cities. The minimal inhibitory concentration (MIC) of antibacterial agents was determined by the broth microdilution method. The sensitive rates and MIC range of the antibiotics were analyzed by the WHONET-5.6 software. RESULTS: Only 19.7%(59/299) S. pneumoniae was sensitive to oral penicillin. The sensitive rates of S. pneumoniae to second-generation cephalosporins(cefuroxime and cefaclor), amoxicillin with clavulanic acid, ceftriaxone, and macrolides (erythromycin, azithromycin and clarithromycin) were 25.6% (77/299), 33.4% (100/299), 63.5% (190/299), and 4.4% (13/299), respectively. About 93.5% (280/299)and 98.0% (293/299)of S. pneumoniae isolates were sensitive to levofloxacin and moxifloxacin.All of the K. pneumoniae isolates were sensitive to ertapenem and imipenem. The sensitive rates of K. pneumoniae to ceftriaxone, cefotaxime, ceftazidime, cefepime, and cefoxitin were about 85.0%, 93.2% (206/221), and 90.3% (200/221)of K. pneumoniae isolates were sensitive to levofloxacin and moxifloxacin.The mean prevalence of ESBL-producing K. pneumoniae was 8.1% (18/221). No S. aureus isolates resistant to vancomycin were detected in this study.The sensitive rates of S. aureus to levofloxacin, moxifloxacin, trimethoprim/sulfamethoxazole, and rifampin were 83.5% (97/116), 82.8% (96/116), 89.6% (104/116) and 83.5% (97/116), respectively. 37.4% (43/116) and 34.8% (40/116)of S. aureus isolates were sensitive to erythromycin and chloramphenicol.All of the H. influenzae and M. catarrhalis isolates were sensitive to amoxicillin with clavulanic acid, ceftriaxone, levofloxacin and moxifloxacin. The sensitive rates of H. influenza and M. catarrhalis to ampicillin, cefuroxime, cefaclor, erythromycin, azithromycin, and clarithromycin were from 80% to 100%. CONCLUSIONS: Penicillins, second-generation cephalosporins (cefuroxime and cefaclor) and amoxicillin with clavulanic acid showed low antimicrobial activity to S. pneumoniae, but a higher sensitive rate to ceftriaxone. The macrolides exhibited a high activity against H. influenza and M. catarrhalis, but low antimicrobial activity against S. pneumoniae and S. aureus. The antimicrobial activity of fluoroquinolones such as levofloxacin and moxifloxacin against most of the respiratory pathogens was high.

Figure-of-merit enhancement in nanostructured FeSb(2-x)Ag(x) with Ag(1-y)Sb(y) nanoinclusions.

We present the figure-of-merit (ZT) improvement in nanostructured FeSb(2-x)Ag(x) with Ag(1-y)Sb(y) nanoinclusions through a metal/semiconductor interface engineering approach. Owing to the interfaces between FeSb(2-x)Ag(x) and Ag(1-y)Sb(y) phases, as well as the identical work functions, both thermal conductivity and electrical resistivity of the nanocomposites were significantly reduced in the lower temperature regime compared with pure FeSb(2). Overall, an improvement of 70% in ZT was achieved for the optimized nanocomposite FeSb(1.975)Ag(0.025)/Ag(0.77)Sb(0.23) sample, in which Ag(0.77)Sb(0.23) is about 10% by molar ratio. The results of this approach clearly demonstrated the metal/semiconductor interface concept and confirmed the potential of strongly correlated material systems as promising thermoelectric materials.

[The review of the composition of Za Liao Fang of Jinguiyaolue (Synopsis of Prescriptions of the Golden Chamber)].

The contents of Jinguiyaolue (Synopsis of Prescriptions of the Golden Chamber) can mainly be divided into 2 parts, which are "text" and "attached formulas". It is mostly thought that the "text" has more content than the "attached formulas". After comparing the small character version of WU Qian's transcript, which was recently published,with the large character version of Jinguiyaolue, and doing textual research on the "attached formulas" in Za Liao Fang of Jinguiyaolue (Synopsis of Prescriptions of the Golden Chamber) according to the clues left by the Bureau of the Revision of Medical Books in Song Dynasty, we can find that there are only "chai hu decoction with addition or subtraction in four seasons" and "the Kele pear pill for taking for long periods" which belong to the Song masters' copy. However, another 22 prescriptions called "attached formulas" were added when the Song masters revised it.

Ultrasensitive chemical detection using a nanocoax sensor.

We report on the design, fabrication, and performance of a nanoporous, coaxial array capacitive detector for highly sensitive chemical detection. Composed of an array of vertically aligned nanoscale coaxial electrodes constructed with porous dielectric coax annuli around carbon nanotube cores, this sensor is shown to achieve parts per billion level detection sensitivity, at room temperature, to a broad class of organic molecules. The nanoscale, 3D architecture and microscale array pitch of the sensor enable rapid access of target molecules and chip-based multiplexing capabilities, respectively.

A molecular-imprint nanosensor for ultrasensitive detection of proteins.

Molecular imprinting is a technique for preparing polymer scaffolds that function as synthetic receptors. Imprinted polymers that can selectively bind organic compounds have proven useful in sensor development. Although creating synthetic molecular-imprinting polymers that recognize proteins remains challenging, nanodevices and nanomaterials show promise in this area. Here, we show that arrays of carbon-nanotube tips with an imprinted non-conducting polymer coating can recognize proteins with subpicogram per litre sensitivity using electrochemical impedance spectroscopy. We have developed molecular-imprinting sensors specific for human ferritin and human papillomavirus derived E7 protein. The molecular-imprinting-based nanosensor can also discriminate between Ca(2+)-induced conformational changes in calmodulin. This ultrasensitive, label-free electrochemical detection of proteins offers an alternative to biosensors based on biomolecule recognition.

Route to GaN and VN assisted by carbothermal reduction process.

A route to prepare nitrides, such as GaN, VN, and other nitrides, is reported. The reaction pathway involves a two-step process by using the as-synthesized a-C3N3.69 as precursor. The route is so potent that a series of nitrides can be directly synthesized from their oxides at moderate temperatures. A striking feature of this method lies in that a-C3N3.69 is found to play double roles as both carbonizing and nitridizing agent in these reactions. These results will greatly deepen our understandings of the mechanism for solid-state metathesis reactions.