Centrosymmetry-Breaking Morphotropic Phase Boundary: A Pathway to Highly Sensitive and Strong Pressure-Responsive Nonlinear Optical Switches.

The quest for high-performance piezoelectric materials has been synonymous with the pursuit of the morphotropic phase boundary (MPB), yet the full potential of MPBs remains largely untapped outside of the realm of ferroelectrics. In this study, we reveal a new class of MPB by creating continuous molecular-based solid solutions between centro- and noncentrosymmetric compounds, exemplified by (tert-butylammonium)1-x(tert-amylammonium)xFeCl4 (0 ≤ x ≤ 1), where the MPB is formed due to disorder of molecular cations. Near the MPB, we discovered an exceptionally sensitive nonlinear optical material in the centrosymmetric phase, capable of activation at pressures as low as 0.12-0.27 GPa, and producing tunable second-harmonic generation (SHG) signals from zero to 18.8 times that of KH2PO4 (KDP). Meanwhile, synchrotron diffraction experiments have unveiled a third competing phase (P212121) appearing at low pressure, forming a triple-phase point near the MPB, thereby providing insight into the mechanism underpinning the nonlinear optical (NLO) switch behavior. These findings highlight the opportunity to harness exceptional physical properties in symmetry-breaking solid solution systems by strategically designing novel MPBs.

High-Tc Ferromagnetic Semiconductor in Thinned 3D Ising Ferromagnetic Metal Fe3GaTe2.

Emergent phenomena in exfoliated layered transition metal compounds have attracted much attention in the past several years. Especially, pursuing a ferromagnetic insulator is one of the exciting goals for stimulating a high-performance magnetoelectrical device. Here, we report the transition from a metallic to high-Tc semiconductor-like ferromagnet in thinned Fe3GaTe2, accompanied with competition among various magnetic interactions. As evidenced by critical exponents, Fe3GaTe2 is the first layered ferromagnet described by a 3D Ising model coupled with long-range interactions. An extra magnetic phase from competition between ferromagnetism and antiferromagnetism emerges at a low field below Tc. Upon reducing thickness, the Curie temperature (Tc) monotonically decreases from 342 K for bulk to 200 K for 1-3 nm flakes, which is the highest Tc reported as far as we know. Furthermore, a semiconductor-like behavior has been observed in such 1-3 nm flakes. Our results highlight the importance of Fe3GaTe2 in searching for ferromagnetic insulators, which may benefit spintronic device fabrication.

Observation of Two-Dimensional Type-II Superconductivity in Bulk 3R-TaSe2 by Scanning Tunneling Spectroscopy.

Here we report a low-temperature and vector-magnetic-field scanning tunneling microscopy/spectroscopy (STM/S) study on 3R-TaSe2. The sample surface was obtained by exfoliating a bulk 3R-TaSe2 single crystal in an ultrahigh-vacuum (UHV) chamber and then transferred in situ to STM. It was observed that the topmost layer shows a 3 × 3 charge density wave pattern at T = 4.2 K with metallic character in STS. The electronic characterization study by variable-temperature and magnetic field STS revealed that 3R-TaSe2 behaves as a type-II superconductor. More intriguingly, such superconductivity (SC) can survive under strong in-plane magnetic fields even up to 2.5 T and out-of-plane magnetic fields up to 0.7 T, exhibiting an anisotropic superconducting property. Temperature-dependent STS showed that 3R-TaSe2 undergoes a transition above 0.58 K. Our results may be important for understanding the intriguing SC properties of the 3R-phase van der Waals materials.

Two-Dimensional Pb Square Nets from Bulk (RO)nPb (R = Rare Earth Metals, n = 1,2).

All two-dimensional (2D) materials of group IV elements from Si to Pb are stabilized by carrier doping and interface bonding from substrates except graphene which can be free-standing. The involvement of strong hybrid of bonds, adsorption of exotic atomic species, and the high concentration of crystalline defects are often unavoidable, complicating the measurement of the intrinsic properties. In this work, we report the discovery of seven kinds of hitherto unreported bulk compounds (RO)nPb (R = rare earth metals, n = 1,2), which consist of quasi-2D Pb square nets that are spatially and electronically detached from the [RO]δ+ blocking layers. The band structures of these compounds near Fermi levels are relatively clean and dominantly contributed by Pb, resembling the electron-doped free-standing Pb monolayer. The R2O2Pb compounds are metallic at ambient pressure and become superconductors under high pressures with much enhanced critical fields. In particular, Gd2O2Pb (9.1 µB/Gd) exhibits an interesting bulk response of lattice distortion in conjunction with the emergence of superconductivity and magnetic anomalies at a critical pressure of 10 GPa. Our findings reveal the unexpected facets of 2D Pb sheets that are considerably different from their bulk counterparts and provide an alternative route for exploring 2D properties in bulk materials.

Superconductivity in an Orbital-Reoriented SnAs Square Lattice: A Case Study of Li0.6 Sn2 As2 and NaSnAs.

Searching for functional square lattices in layered superconductor systems offers an explicit clue to modify the electron behavior and find exotic properties. The trigonal SnAs3 structural units in SnAs-based systems are relatively conformable to distortion, which provides the possibility to achieve structurally topological transformation and higher superconducting transition temperatures. In the present work, the functional As square lattice was realized and activated in Li0.6 Sn2 As2 and NaSnAs through a topotactic structural transformation of trigonal SnAs3 to square SnAs4 under pressure, resulting in a record-high Tc among all synthesized SnAs-based compounds. Meanwhile, the conductive channel transfers from the out-of-plane pz orbital to the in-plane px +py orbitals, facilitating electron hopping within the square 2D lattice and boosting the superconductivity. The reorientation of p-orbital following a directed local structure transformation provides an effective strategy to modify layered superconducting systems.

Surface microstructures of lunar soil returned by Chang'e-5 mission reveal an intermediate stage in space weathering process.

The lunar soils evolution over time is mainly caused by space weathering that includes the impacts of varying-sized meteoroids and charged particles implantation of solar/cosmic winds as well. It has long been established that space weathering leads to the formation of outmost amorphous layers (50-200 nm in thickness) embedded nanophase iron (npFe0) around the mineral fragments, albeit the origin of the npFe0 remains controversial . The Chang'e-5 (CE-5) mission returned samples feature the youngest mare basalt and the highest latitude sampling site , providing an opportunity to seek the critical clues for understanding the evolution of soils under space weathering. Here, we report the surface microstructures of the major minerals including olivine, pyroxene, anorthite, and glassy beads in the lunar soil of CE-5. Unlike the previous observations, only olivine in all crystals is surrounded by a thinner outmost amorphous SiO2 layer (∼10 nm thick) and embedded wüstite nanoparticles FeO (np-FeO, 3-12 nm in size) instead of npFe0. No foreign volatile elements deposition layer and solar flare tracks can be found on the surface or inside the olivine and other minerals. This unique rim structure has not been reported for any other lunar, terrestrial, Martian, or meteorite samples so far. The observation of wüstite FeO and the microstructures support the existence of an intermediate stage in space weathering for lunar minerals by thermal decomposition.

Superatomic-Charge-Density-Wave in Cluster-Assembled Au6Te12Se8 Superconductors.

Superatomic crystals are a class of hierarchical materials composed of atomically precise clusters assembled via van der Waals or covalent-like interactions. Au6Te12Se8, an all-inorganic superatomic superconductor exhibiting superatomic-charge-density-wave (S-CDW), provides the first platform to study the response of its collective quantum phenomenon to the external pressure in superatomic crystals. We reveal a competition between S-CDW and superconductivity in an ultra-narrow pressure range. Distinct from conventional CDW ordering, S-CDW shows the lowest threshold (0.1 GPa) toward external pressure that is 1-2 orders of magnitude lower than other atomic compounds. Prominently, a second superconducting phase emerges above 7.3 GPa with a threefold enhancement in the transition temperature (Tc) to 8.5 K, indicating a switch of the conduction channel from the a- to b-axis. In situ synchrotron diffractions and theoretical calculations reveal a pressure-mediated mesoscopic slip of the superatoms and a 2D-3D transition of the Fermi surface topology, which well explains the observed dimensional crossover of conductivity and re-entrant superconductivity.

Spatially Separated Superconductivity and Enhanced Charge-Density-Wave Ordering in an IrTe2 Nanoflake.

The interplay among collective electronic states like superconductivity (SC) and charge density wave (CDW) is of significance in transition metal dichalcogenides. To date, a consensus on the relationship between SC and CDW has not been established in IrTe2. Here we use the Au-assisted exfoliation method to cleave IrTe2 down to 10 nm. A striking feature is the concurrence of phase separation in a single piece of nanoflake, i.e., the superconducting (P3̅m1) and CDW (P3̅) phases. In the former area, the dimensional fluctuations suppress the CDW ordering and induce SC at 3.5 K. The CDW area at the phase boundary shows enhanced TCDW at 605 K (TCDW = 280 K in the bulk phase), which is accompanied by a unique wrinkle. Detailed analyses suggest that the strain-induced bond breaking of Te-Te dimers favors the CDW. Our works provide compelling evidence of competition between SC and CDW in IrTe2.

Competition of Superconductivity and Charge Density Wave in Selective Oxidized CsV_{3}Sb_{5} Thin Flakes.

The recently discovered layered kagome metals AV_{3}Sb_{5} (A=K, Rb, and Cs) with vanadium kagome networks provide a novel platform to explore correlated quantum states intertwined with topological band structures. Here we report the prominent effect of hole doping on both superconductivity and charge density wave (CDW) order, achieved by selective oxidation of exfoliated thin flakes. A superconducting dome is revealed as a function of the effective doping content. The superconducting transition temperature (T_{c}) and upper critical field in thin flakes are significantly enhanced compared with the bulk, which are accompanied by the suppression of CDW. Our detailed analyses establish the pivotal role of van Hove singularities in promoting correlated quantum orders in these kagome metals. Our experiments not only demonstrate the intriguing nature of superconducting and CDW orders, but also provide a novel route to tune the carrier concentration through both selective oxidation and electric gating. This establishes CsV_{3}Sb_{5} as a tunable 2D platform for the further exploration of topology and correlation among 3d electrons in kagome lattices.

Efficient and stable Sr3Eu2B4O12 red phosphor benefiting from low symmetry and distorted local environment.

The development of suitable red phosphors to obtain improved white color stands a good chance to serve in the new generation of white light-emitting diodes. Owing to multi-elements via doping and oxidation of reduced valence state of lanthanide or transition metal ions, most of the reported phosphors usually suffer from complex synthetic processes and unstable color of the lighting industry cycle. In this work, we present a new red emitting and stable Sr3Eu2B4O12 phosphor with regard to its special structure. It crystallizes as an orthorhombic cell, with Sr and Eu atoms co-occupying three different lattice sites in the space group of Pnma (no. 62). It is proposed that the long bond distance between activators minimizes the content quenching, while the high disorder of location restricts the thermal quenching. This phosphor emits bright red light with good color purity under UV excitation, with the luminescence intensity and quantum yield tunable via the fabrication temperature. Through a preliminary optimization of the synthesis process, the Sr3Eu2B4O12 phosphor prepared at 1250 °C has high quantum yields of about 94.7% and excellent thermal stability of 85.6% intensity retention at 150 °C relative to the initial value at room temperature. The calculated Judd-Ofelt intensity parameters (Ω2, Ω4) further clarified that the Eu3+ site in Sr3Eu2B4O12 had lower symmetry without an inversion center, and more distorted local environment and structural rigidity of the host, predicting excellent thermal stability. Finally, a warm pc-WLED device has been produced by mixing as-prepared Sr3Eu2B4O12 powders and commercial BaMgAl10O17:Eu2+ and (Sr, Ba)2SiO4:Eu2+ phosphors, which exhibits a high color rendering index (Ra = 83.4) along with a color temperature at around 4102 K. The present work indicates that the Sr3Eu2B4O12 phosphor is an efficient red component with excellent thermal stability for white-light production of near-UV-excited w-LEDs.

Structure and Transport Properties in Itinerant Antiferromagnet RE2(Ni1- xCu x)5As3O2 (RE = Ce, Sm).

We report the crystal structure and physical properties of two Ni5As3-based compounds RE2Ni5As3O2 (RE = Ce, Sm). The former exhibits structural phase transition from tetragonal (space group I4/ mmm, 139) to orthorhombic (space group Immm, 71) symmetry at 230 K, while the latter undergoes a charge-density-wave-like structural distortion with abrupt change of Ni-As bond length. Both compounds show antiferromagnetic transitions due to RE3+ ions ordering at 4.4 and 3.4 K, accompanying with the large enhancement of Sommerfeld coefficients comparing to the nonmagnetic La analogue. Although the Cu substitution for Ni induces structural anomalies and suppression of structural transition like the behaviors in La/Pr/Nd analogues, the superconductivity is not observed in both Cu-doped RE2Ni5As3O2 (RE = Ce, Sm) above 0.25 K. Our structural refinements reveal that the lacking of superconductivity in RE2(Ni1- xCu x)5As3O2 might relate to the anomalous increase of As height, h1.

Vaccination demonstration zone successfully controls rabies in Guangxi Province, China.

BACKGROUND: Guangxi is the province most seriously affected by rabies virus (RABV) in China. Those most affected by RABV each year are people in rural areas, where dogs are the main cause of human infection with the virus. METHODS: In this study, we established a rabies vaccination demonstration program that included eradication, core, and peripheral areas. This program was implemented for 9 years and comprised three stages: 12 counties in the first stage (2008-2010), 21 counties in the second stage (2011-2013), and then extending to all counties of Guangxi Province in the third stage (2014-2016). The program included a dog vaccination campaign, surveillance of clinically healthy dogs who may be potential RABV carriers, monitoring anti-RABV antibody titers in vaccinated dogs, and compiling and reporting statistics of human rabies cases. RESULTS: The target effectiveness was achieved in the eradication, core, and peripheral areas in all three stages. The vaccination demonstration program successfully promoted RABV vaccination of domestic dogs throughout Guangxi Province by drawing upon the experience gained at key points. Compared with a vaccination coverage rate of 39.42-46.85% in Guangxi Province overall during 2003-2007, this rate gradually increased to 48.98-52.67% in 2008-2010, 60.24-69.67% in 2011-2013, and 70.09-71.53% in 2014-2016, thereby meeting World Health Organization requirements. The total cases of human rabies in the province decreased from 602 in 2004 to 41 cases in 2017. CONCLUSIONS: The present pilot vaccination program obviously increased the rabies vaccination and seroconversion rates, and effectively reduced the spread of rabies from dogs to humans as well as the number of human rabies cases, thus successfully controlling rabies in Guangxi.

Chirality-dependent anisotropic elastic properties of a monolayer graphene nanosheet.

An analytical approach is presented to predict the elastic properties of a monolayer graphene nanosheet based on interatomic potential energy and continuum mechanics. The elastic extension and torsional springs are utilized to simulate the stretching and angle variation of carbon-carbon bond, respectively. The constitutive equation of the graphene nanosheet is derived by using the strain energy density, and the analytical formulations for nonzero elastic constants are obtained. The in-plane elastic properties of the monolayer graphene nanosheet are proved to be anisotropic. In addition, Young's moduli, Poisson's ratios and shear modulus of the monolayer graphene nanosheet are calculated according to the force constants derived from Morse potential and AMBER force field, respectively, and they were proved to be chirality-dependent. The comparison with experimental results shows a very agreement.

Deformation mechanisms of carbon nanotube fibres under tensile loading by in situ Raman spectroscopy analysis.

Deformation mechanisms of carbon nanotube (CNT) fibres under tensile loading are studied by means of in situ Raman spectroscopy to detect the CNT deformation and stress distributions in the fibres. The G' band in the Raman spectrum responds distinctly to the tensile stress in Raman shift, width and intensity. The G' band changes with the tensile deformation of the fibre at different stages, namely elastic deformation, strengthening and damage-fracture. It is deduced that the individual CNTs only deform elastically without obvious damage or bond breaking. The yield and fracture of fibres can be due to the slippage among the CNTs.

Instability analysis of torsional MEMS/NEMS actuators under capillary force.

The static and dynamic instabilities of a torsional MEMS/NEMS actuator caused by capillary effects are studied, respectively. An instability number, eta, is defined, and the critical gap distance, g(cr), between the mainplate and the substrate is derived. According to the values of eta and g, the instability criteria of the actuator are presented. The dimensionless motion equation of the MEMS/NEMS torsional actuator is derived when it makes nonlinear oscillation under capillary force. The qualitative analysis of the nonlinear equation is made, and the phase portraits are presented on the phase plane. In addition, the bifurcation phenomena in the system are also analyzed.

[Study on the molecular epidemiology of Streptococcus suis type 2 from healthy pigs in Guangxi].

OBJECTIVE: In order to investigate the positive rate of streptococcus suis type 2 and the genes of their suilysin (sly), extracellular protein (epf) and muramidasa-released protein ( mrp) and to understand the antibiotic susceptibility of S. suis type 2. METHODS: S. suis type 2, isolated from slaughtered healthy pig's tonsil in 10 county area of Guangxi, were identified by Multiplex PCR, and the genes of their sly, epf, mrp and the antimicrobial sensitivity analysis were performed. RESULTS: 1105 strains of Streptococcus including 667 strains of S. suis and 33 strains of S. suis type 2 were detected from 1179 samples. In these S. suis type 2 strains, there were 22 strains of sly + mrp + epf+ type,1 strain of sly + mrp + epf - type, 2 strains of sly - mrp + epf + type, 7 strains of sly - mrp + epf - type and 1 strain of sly - mrp - epf- type. When these strains were subjected to be tested with penicillin, eritrocina, vacocin, gentamycin, specti-nomysin, enraxacin, ciprofloxaxin, cephalothin VI, sulfadiazine sodium, cyantin, mycifradin, amikacin and achromcin, some were found to be resistant to but most strains were susceptible to cephalothin VI, penicillin and enraxacin. There were 31, 29 and 27 strains over medium sensitivity, respectively, but 28 and 27 resistant strains to amikacin and achromcin were found. CONCLUSION: The positive rate of S. suis type 2 in clinical healthy pigs was low (2.8%) and did not show obvious difference between the counties with or without a history of S. suis infection. All the isolated strains were susceptible to cephalothin VI, but most strains were virulent.

Molecular epidemiology of rabies in Guangxi Province, south of China.

BACKGROUND: Surveillance data for rabies in Guangxi Province in China showed that human rabies cases have gradually increased since 1996. OBJECTIVE: To evaluate the epidemiology of rabies at the molecular level and provide suggestions for effective prevention of rabies in Guangxi. STUDY DESIGN: Since 2000, 1569 brains from suspected rabid animals were collected from different areas of Guangxi. Rabies virus was isolated from 42 samples. RT-PCR was used to amplify a 455 nucleotide segment of the 3'-terminal of the N gene. The sequencing data from that segment was used for phylogenetic analysis. RESULTS: Nucleotide homology comparisons and phylogenetic tree analysis based on this sequence indicated that all the rabies virus isolates from Guangxi belonged to genotype 1 and could be divided into four groups. Groups I, II and IV included 23, 10 and 8 isolates, respectively. These had nucleotide homologies of 97.1-100%, 98.2-100% and 99.1-99.6%, respectively. Only the GXN119 strain belonged to group III. Group I had two group-specific mutations: T90N and E110D. Group II had one group-specific mutation of T42S. CONCLUSIONS: This study showed that rabies virus isolates from Guangxi have a close genetic relationship and topographical distribution.

[Effect of five species of Epimedium on growth of cartilage and proliferation of cartilage cell in vitro].

OBJECTIVE: To observe the effect of Epimedium brevicornum, E. sagittatum, E. koreanum, E, wushanense and E. elongntum on the growth of cartilage and proliferation of cartilage cell in vitro. METHOD: According to the paired design method, either femur of each chichen embryo was put into the control tube with the medium containing no Epimedium injection, and the other was put into the treated tube with the medium containing 3% Epimedium injection. The length and weight of cultured cartilage and proliferation of cartilage cell (MTY method) were used as the indices to observe the cartilage biological activities of the five species of Epimedium in culture. RESULT: The results showed that the indices of length, weight and MTT in the E. brevicornum and E. sagittatum group were significantly higher than those in the contral group, but the above indices in groups E. koreanum, E. wushanens and E. elongntum were similar to those of the control with no statistical difference. CONCLUSION: E. brevicornum and E. sagittatum can improve the growth of cartilage and proliferation of cartilage cell in vitro, and other three Epimedium have not the same effect in this test.