The superconductor Sr4V2O6Fe2As2 with transition temperature at 37.2 K has been fabricated. It has a layered structure with the space group of p4/nmm, and with the lattice constants a = 3.9296Å and c = 15.6732Å. The observed large diamagnetization signal and zero-resistance demonstrated the bulk superconductivity. The broadening of resistive transition was measured under different magnetic fields leading to the discovery of a rather high upper critical field. The results also suggest a large vortex liquid region which reflects high anisotropy of the system. The Hall effect measurements revealed dominantly electron-like charge carriers in this material. The superconductivity in the present system may be induced by oxygen deficiency or the multiple valence states of vanadium.Since the discovery of superconductivity 1 at 26 K in oxy-arsenide LaF eAsO 1−x F x , tremendous attention has been paid to searching new superconductors in this family. Among the superconductors with several different structures, 2,3,4,5,6 the highest T c has been raised to 55-56 K 7,8,9,10,11 in doped oxy-iron-arsenides (F-doped LnFeAsO, the so-called 1111 phase, Ln=rare earth elements) or the fluoride derivative iron-arsenides (Lndoped AEFeAsF, AE=alkaline earth elements).12 The superconductivity can also be induced by applying a high pressure to the undoped parent samples.13,14 Although it remains unclear what governs the mechanism of superconductivity in the FeAs-based system, it turns out to be clear that the parent phase is accompanied by an antiferromagnetic (AF) order and the superconductivity can be induced by suppressing this magnetic order. A typical example was illustrated in the (Ba, Sr)F e 2 As 2 (so-called 122) system, the AF order is suppressed and superconductivity was induced by either doping K to the Ba or Sr sites, 2,15,16 or doping Co to the Fe sites. 17,18 On the other hand, superconductivity was also found in the parent phase of FeP-based system, such as LaFePO (T c = 2.75K)19 , or in LiFeAs. 3,4 Very recently superconductivity at about 17 K was found in another FeP based parent compound Sr 4 Sc 2 O 6 Fe 2 P 2 (so-called 42622).20 Due to the absence of the AF order in the superconductors mentioned above, one naturally questions whether the AF order is a prerequisite for the superconductivity in the iron-pnictide system. As far as we know, no superconductivity was detected in the parent phase of some FeAs-based compounds, including the 1111, 122 and the recently discovered 42622 and 32522 phases. 21,22,23,24,25 Although some trace of superconductivity was reported in the doped FeAs-based 42622 or 32522 compounds, the high-T c superconductivity was not supported by a clear large diamagnetization signal. 22,23 In this Letter, we report the discovery of superconductivity at about 37.2 K in the new compound Sr 4 V 2 O 6 Fe 2 As 2 . This work presents the unambiguous evidence for high temperature superconductivity in the FeAs-based 42622 system. The polycrystalline samples were synthesized by using a two-step solid state re...

The discovery of iron-based superconductors (FeSCs), with the highest transition temperature (Tc) up to 55 K, has attracted worldwide research efforts over the past ten years. So far, all these FeSCs structurally adopt FeSe-type layers with a square iron lattice and superconductivity can be generated by either chemical doping or external pressure. Herein, we report the observation of superconductivity in an iron-based honeycomb lattice via pressure-driven spin-crossover. Under compression, the layered FePX3 (X = S, Se) simultaneously undergo large in-plane lattice collapses, abrupt spin-crossovers, and insulator-metal transitions. Superconductivity emerges in FePSe3 along with the structural transition and vanishing of magnetic moment with a starting Tc ~ 2.5 K at 9.0 GPa and the maximum Tc ~ 5.5 K around 30 GPa. The discovery of superconductivity in iron-based honeycomb lattice provides a demonstration for the pursuit of transition-metal-based superconductors via pressure-driven spin-crossover.

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By substituting the Fe with the 4d-and 5d-transition metals Rh, Ir, and Pd in SrFe 2 As 2 , we have successfully synthesized a series of superconductors SrFe 2−x M x As 2 ͑M = Rh, Ir, and Pd͒ and explored the phase diagrams of them. The systematic evolution of the lattice constants indicated that part of the Fe ions were successfully replaced by the transition metals Rh, Ir, and Pd. By increasing the doping content of Rh, Ir, and Pd, the antiferromagnetic ͑AF͒ state of the parent phase is suppressed progressively and superconductivity is induced. The general phase diagrams were obtained and found to be similar to the case of doping Co and Ni to the Fe sites. However, the detailed structure of the phase diagram, in terms of how fast to suppress the antiferromagnetic order and induce the superconductivity, varies from one kind of doped element to another. Regarding the close values of the maximum superconducting transition temperatures in doping Co, Rh, and Ir which locate actually in the same column in the periodic table of elements but have very different masses, we argue that the superconductivity is intimately related to the suppression of the AF order, rather than the electron-phonon coupling.

Solar-energy-driven conversion of CO 2 into hydrocarbon fuels can simultaneously generate chemical fuels to meet energy demand and mitigate rising CO 2 levels. The utilization of the clean and renewable solar power resource is, on a longterm basis, an essential component of solutions to address growing global energy demand, which is projected to be 40 TW by 2050. [1] This is because the solar energy received on the earths surface in one hour exceeds current total global energy demand. From the perspective of climate change, expansion of the current fossil fuel-based energy infrastructure to meet the projected energy demand is predicted to add 2986-7402 Gt of CO 2 to the atmosphere by 2100, resulting in a mean rise in global temperature of 2.4-4.5 8C. [2] Since the discovery of the photoreduction of carbon dioxide to form organic compounds using semiconductors by Fujishima and co-workers in 1979, [3] a growing interest in the development of catalysts that are capable of solar-based capture and storage of CO 2 has evolved. [4] Titanium dioxide, which is a cost-efficient, non-toxic and abundant n-type semiconductor, has been widely considered in the solar-driven reduction of CO 2 . Owing to its large band-gap energy of 3-3.2 eV, TiO 2 without doping or post-synthesis treatments can absorb only the ultraviolet portion of the solar spectrum. To narrow the band-gap of TiO 2 and improve its photocatalytic performance, strategies such as compositional doping or deliberately introducing disorder in crystalline TiO 2 are being investigated. [5] Herein, we demonstrate an approach that is able to achieve high-rate sunlight-driven conversion of diluted CO 2 to light hydrocarbons in which an optimized combination of a Cu-Pt coating and modulated-diameter TiO 2 nanotubes are used as the photocatalyst. We demonstrate at least a fourfold improvement in CO 2 conversion rates over prior art [6] by using a catalyst consisting of coaxial Cu-Pt bimetallic shells supported on a periodically modulated double-walled TiO 2 nanotube (PMTiNT) array core. The photocatalytic reaction occurs at room temperature and generates CH 4 , C 2 H 4 , and C 2 H 6 as reaction products. Under AM 1.5 one-sun illumination, using 99.9 % CO 2 , we obtained a hydrocarbon production rate of 3.51 mL g À1 h À1 or 574 nmol cm À2 h À1 . A key novelty is the effectiveness of our photocatalyst for the photoreduction of unconcentrated CO 2 . When the Cu 0.33 -Pt 0.67 /PMTiNT heterogeneous catalyst was utilized for the photoreduction of diluted CO 2 (0.998 % in N 2 ) at 25 8C, we found an average hydrocarbon production rate of 3.7 mL g À1 h À1 or 610 nmol cm À2 h À1 . The periodic modulation of the diameters of the nanotube arrays increased the surface area and improved the utilization of light while the bimetallic coating increased catalyst activity and specificity. Our version of a highly active CO 2 reduction system does not require reactant gases with high purities and could potentially be used to photocatalytically capture CO 2 directly from air or from flue gas...

We have successfully synthesized the fluo-arsenide SrFeAsF, a new parent phase with the ZrCuSiAs structure. The temperature dependence of resistivity and dc magnetization both reveal an anomaly at about Tan = 173 K, which may correspond to the structural and/or Spin-Density-Wave (SDW) transition. Strong Hall effect and moderate magnetoresistance were observed below Tan. Interestingly, the Hall coefficient RH is positive below Tan, which is opposite to the cases in the two parent phases of FeAs-based systems known so far, i.e., LnFeAsO (Ln = rare earth elements) and (Ba, Sr)Fe2As2 where the Hall coefficient RH is negative. This strongly suggests that the gapping of the Fermi surface induced by the SDW order leaves one of the hole pockets fully or partially ungapped in SrFeAsF. Our data show that it is possible for the parent phases of the arsenide superconductors to display dominant carriers that are either electronlike or holelike.PACS numbers: 74.70. Dd, 74.25.Fy, 75.30.Fv, 74.10.+v The discovery of superconductivity in the quaternary compound LaFeAsO 1−x F x which is abbreviated as the FeAs-1111 phase, has attracted great attentions in the fields of condensed matter physics and material sciences.1 The family of the FeAs-based superconductors has been extended rapidly. As for the FeAs-1111 phase, most of the discovered superconductors are characterized as electron-doped ones and the superconducting transition temperature has been quickly raised to T c = 55∼ 56 K via replacing lanthanum with other rare earth elements. 2,3,4,5,6,7 Meanwhile, the first holedoped superconductor La 1−x Sr x FeAsO with T c ≈ 25 K was discovered, 8,9 followed with the observation of superconductivity in hole-doped Nd 1−x Sr x FeAsO 10 and Pr 1−x Sr x FeAsO.11 Later on, (Ba, Sr) 1−x K x Fe 2 As 2 which is denoted as FeAs-122 for simplicity 12,13,14 , and Li x FeAs as an infinite layered structure (denoted as FeAs-111) were discovered. 15,16,17 It is assumed that the superconductivity both in the FeAs-1111 phase and FeAs-122 phase is intimately connected with a Spin-DensityWave (SDW) anomaly in the FeAs layers.12,18 For undoped LaFeAsO, an SDW-driven structural phase transition around 150 K was found.19 It seems that any new parent phase will initiate a series of new superconductors by doping it away from the state with features of a bad metal and the SDW order.In this paper, we report the discovery of a new FeAsbased layered compound SrFeAsF which has the ZrCuSiAs structure. As we know SrZnPF is a compound with the ZrCuSiAs structure 20 . We replace the ZnP sheets with FeAs sheets and get a new compound of SrFeAsF. The compound SrFeAsF has the tetragonal space group P4/nmm at 300 K. Both the resistivity and the dc magnetic susceptibility exhibit a clear anomaly at about 173 K, which is attributed to the structural and/or SDW transition. Surprisingly, a positive Hall coefficient R H has been found implying a dominant conduction by holelike charge carriers in this parent phase.The SrFeAsF samples were prepared using a two-step solid s...

The controllable isotropic thermal expansion with a broad coefficient of thermal expansion (CTE) window is intriguing but remains challenge. Herein we report a cubic MZrF series (M = Ca, Mn, Fe, Co, Ni and Zn), which exhibit controllable thermal expansion over a wide temperature range and with a broader CTE window (-6.69 to +18.23 × 10/K). In particular, an isotropic zero thermal expansion (ZTE) is achieved in ZnZrF, which is one of the rarely documented high-temperature isotropic ZTE compounds. By utilizing temperature-dependent high-energy synchrotron X-ray total scattering diffraction, it is found that the flexibility of metal···F atomic linkages in MZrF plays a critical role in distinct thermal expansions. The flexible metal···F atomic linkages induce negative thermal expansion (NTE) for CaZrF, whereas the stiff ones bring positive thermal expansion (PTE) for NiZrF. Thermal expansion could be transformed from striking negative, to zero, and finally to considerable positive though tuning the flexibility of metal···F atomic linkages by substitution with a series of cations on M sites of MZrF. The present study not only extends the scope of NTE families and rare high-temperature isotropic ZTE compounds but also proposes a new method to design systematically controllable isotropic thermal expansion frameworks from the perspective of atomic linkage flexibility.