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Red phosphorus offers a high theoretical sodium capacity and has been considered as a candidate anode for sodium-ion batteries. Similar to silicon anodes for lithium-ion batteries, the electrochemical performance of red phosphorus is plagued by the large volume variation upon sodiation. Here we perform in situ transmission electron microscopy analysis of the synthesized red-phosphorus-impregnated carbon nanofibers with the corresponding chemo-mechanical simulation, revealing that, the sodiated red phosphorus becomes softened with a “liquid-like” mechanical behaviour and gains superior malleability and deformability against pulverization. The encapsulation strategy of the synthesized red-phosphorus-impregnated carbon nanofibers has been proven to be an effective method to minimize the side reactions of red phosphorus in sodium-ion batteries, demonstrating stable electrochemical cycling. Our study provides a valid guide towards high-performance red-phosphorus-based anodes for sodium-ion batteries., Red phosphorus is a promising anode for Na-ion batteries but suffers from large volume change upon cycling. Here the authors show a red-phosphorus-impregnated carbon nanofiber design in which the sodiated red phosphorus is featured by a “liquid-like” behavior and ultra-stable electrochemical performance is realized.

The rare-earth germanium sulfide iodides RE3Ge2S8I (RE = La, Ce, Pr) have been prepared by reaction of the elements at 900 °C. They adopt the monoclinic La3(SiO4)2Cl-type structure (space group C2/c, Z = 4; a = 16.156(4)–15.9760(9) A, b = 7.9776(18)–7.8786(5) A, c = 11.081(3)–10.9281(6) A, β = 98.192(5)–98.4525(10)° on progressing from La to Pr for the RE component) consisting of isolated thiogermanate tetrahedral groups [GeS4]4– separated by RE3+ and I− ions. The optical band gaps fall in the range of 2.7–3.1 eV. Magnetic measurements indicated simple paramagnetic behaviour for Ce3Ge2S8I and Pr3Ge2S8I.

Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report...

Copper is a common current collector at the anode side in rechargeable batteries. The reactivity of copper is often neglected in battery applications which becomes a problem if the active material is highly reactive as well. Corrosion and compound formation results. Here, we report on the influence of the synthesis method and the role of copper on the electrochemical performance of black phosphorus anodes for sodium ion batteries. Two top-down and one bottom-up approaches were applied to prepare different samples. An easy dip coating process was developed to apply copper prior to usage significantly increasing the capacity of the system.

We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12) were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO2 nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP@TiO2 emerged to be the most active among the polyphosphide@TiO2 materials. The improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge transfer resistance which facilitated better charge separation from inorganic phosphides to TiO2.

Moiré superlattices of van der Waals heterostructures provide a powerful way to engineer electronic structures of two-dimensional materials. Many novel quantum phenomena have emerged in graphene and transition metal dichalcogenide moiré systems. Twisted phosphorene offers another attractive system to explore moiré physics because phosphorene features an anisotropic rectangular lattice, different from isotropic hexagonal lattices previously reported. Here we report emerging anisotropic moiré optical transitions in twisted monolayer/bilayer phosphorenes. The optical resonances in phosphorene moiré superlattice depend sensitively on twist angle and are completely different from those in the constitute monolayer and bilayer phosphorene even for a twist angle as large as 19°. Our calculations reveal that the Γ-point direct bandgap and the rectangular lattice of phosphorene give rise to the remarkably strong moiré physics in large-twist-angle phosphorene heterostructures. This work highlights fresh opportunities to explore moiré physics in phosphorene and other van der Waals heterostructures with different lattice configurations., Twisted phosphorene offers another attractive system to explore moiré physics. Here, the authors report emerging anisotropic moiré optical resonances in twisted monolayer/bilayer phosphorene, exhibiting strong twist dependence for angles as large as 19°.

Tin iodide phosphide (SnIP), an inorganic double-helix material, is a quasi-1D van der Waals semiconductor that shows promise in photocatalysis and flexible electronics. However, the understanding of the fundamental photophysics and charge transport dynamics of this new material is limited. Here, time-resolved terahertz (THz) spectroscopy is used to probe the transient photoconductivity of SnIP nanowire films and measure the carrier mobility. With insight into the highly anisotropic electronic structure from quantum chemical calculations, an electron mobility as high as 280 cm2 V-1 s-1 along the double-helix axis and a hole mobility of 238 cm2 V-1 s-1 perpendicular to the double-helix axis are detected. Additionally, infrared-active (IR-active) THz vibrational modes are measured, which shows excellent agreement with first-principles calculations, and an ultrafast photoexcitation-induced charge redistribution is observed that reduces the amplitude of a twisting mode of the outer SnI helix on picosecond timescales. Finally, it is shown that the carrier lifetime and mobility are limited by a trap density greater than 1018 cm-3 . The results provide insight into the optical excitation and relaxation pathways of SnIP and demonstrate a remarkably high carrier mobility for such a soft and flexible material, suggesting that it could be ideally suited for flexible electronics applications.

Phosphorene—the monolayered material of the element allotrope black phosphorus (Pblack)—and SnIP are 2D and 1D semiconductors with intriguing physical properties. Pblack and SnIP have in common that they can be synthesized via short way transport or mineralization using tin, tin(IV) iodide and amorphous red phosphorus. This top‐down approach is the most important access route to phosphorene. The two preparation routes are closely connected and differ mainly in reaction temperature and molar ratios of starting materials. Many speculative intermediates or activator side phases have been postulated especially for top‐down Pblack/phosphorene synthesis, such as Hittorf's phosphorus or Sn24P19.3I8 clathrate. The importance of phosphorus‐based 2D and 1D materials for energy conversion, storage, and catalysis inspired us to elucidate the formation mechanisms of these two compounds. Herein, we report on the reaction mechanisms of Pblack/phosphorene and SnIP from P4 and SnI2 via direct gas phase formation., 1D‐SnIP and 2D‐phosphorene are formed in a gas phase reaction of gaseous white phosphorus (P4) and SnI2 via P4 activation followed by successive helix or layer growth. P4 activation takes place by Sn2I4 dimers attracting the P lone pairs (SnIP) or direct SnI2 insertion in a P−P bond (phosphorene). Both reaction mechanisms were studied between 0 K and synthesis temperature.

Tin iodide phosphorus (SnIP) is an interesting new semiconductor that is the world's first non-templated inorganic double helix. Here we report on the first ultrafast study of SnIP, where we use THz spectroscopy to measure the carrier mobility and probe the relaxation dynamics. Additionally, we observe a vibrational mode at 1.49 THz and show how carrier screening reduces the oscillator amplitude, which manifests as a reduction in differential signal with Lorentzian lineshape.

SnIP, an atomic-scale inorganic double helix compound is composed of a hexagonal rod packing of double helices in the bulk phase. A racemic mixture of P- and M-SnIP double helices is energetically most favored and present in the solid. In order to evaluate if enantiomer-pure SnIP might be able to realize three different stacking models of seven chiral double helices, an enantiomer-pure, a 2:1, and a racemic 1:1 ratio were investigated according to their energies of formation. While a top-down approach did not lead to single isolated double helices, the development of a bottom-up approach might be beneficial. Motivated by templating strategies in confined geometries we performed first principles density functional theory (DFT) calculations using carbon nanotubes (CNTs) featuring different electronic properties and suitable sizes as matrices to accommodate chiral SnIP double helices. With the aid of DFT, we determined the ideal diameter, stability, and electronic properties of different SnIP@CNT systems. Appropriate molecular starting materials and a feasible formation mechanism are identified based on chemical considerations. An interaction between the CNTs and the SnIP units is evident, causing structure and property modifications of the hybrids. The intercalation of SnIP into a suitable CNT leads to a gain in total energy compared to the isolated systems. Based on our findings, a straightforward way to introduce chirality in suitable CNTs via SnIP@CNT hybrids is feasible.

Layered black phosphorus (BP) has attracted wide attention for mid-infrared photonics and high-speed electronics, due to its moderate band gap and high carrier mobility. However, its intrinsic band gap of around 0.33 electronvolt limits the operational wavelength range of BP photonic devices based on direct interband transitions to around 3.7 μm. In this work, we demonstrate that black arsenic phosphorus alloy (b-AsxP1–x) formed by introducing arsenic into BP can significantly extend the operational wavelength range of photonic devices. The as-fabricated b-As0.83P0.17 photodetector sandwiched within hexagonal boron nitride (hBN) shows peak extrinsic responsivity of 190, 16, and 1.2 mA/W at 3.4, 5.0, and 7.7 μm at room temperature, respectively. Moreover, the intrinsic photoconductive effect dominates the photocurrent generation mechanism due to the preservation of pristine properties of b-As0.83P0.17 by complete hBN encapsulation, and these b-As0.83P0.17 photodetectors exhibit negligible transport hystere...

Electrospinning is used to fabricate sodium ion conducting fiber membranes composed of polyethylene oxide (PEO), sodium tetrafluoroborate (NaBF4), and succinonitrile (SN) as plasticizer. As compared to conventionally prepared lithium electrolyte membranes with identical composition (PEO:SN:LiBF4), those membranes exhibit conductivities up to 10−4 S cm−1 at 328 K (activation energy ∼36 kJ mol−1, 36:8:1 membrane), which favors such systems as a solid-state electrolyte alternative for batteries. The conduction mechanism is evaluated and the ion mobility are examined. We identified the segment mobility of the polyethylene oxide as the main driving force for the enhanced ion mobility in the membranes. The introduction of SN has only a minor influence on the conductivity and segment mobility at room temperature, but extents the anion and cation mobility to temperatures below ambient. For the 36:8:1 (PEO:SN:NaBF4) membrane we found the highest ion mobility of all membranes under investigation. A comparison of the present sodium membranes with lithium systems of the same composition shows that the overall performance of the sodium systems is comparable. Taking plasticizer-free sodium membranes into account they perform even better than the lithium containing counterparts, and plasticizer-modified membranes show only half an order of magnitude lower conductivities than comparable lithium ones.

Two-dimensional (2D) nanoflakes have emerged as a class of materials that may impact electronic technologies in the near future. A challenging but rewarding work is to experimentally identify 2D materials and explore their properties. Here, we report the synthesis of a layered material, P20.56(1)Sb0.44(1), with a systematic study on characterizations and device applications. This material demonstrates a direct band gap of around 1.67 eV. Using a laser-cutting method, the thin flakes of this material can be separated into multiple segments. We have also fabricated field effect transistors based on few-layer P20.56(1)Sb0.44(1) flakes with a thickness down to a few nanometers. Interestingly, these field effect transistors show strong photoresponse within the wavelength range of visible light. At room temperature, we have achieved good mobility values (up to 58.96 cm2/V·s), a reasonably high on/off current ratio (∼103), and intrinsic responsivity up to 10 μA/W. Our results demonstrate the potential of P20.56(...

The majority of research activities on LiCoPO 4 are focused on the phospho-olivine (space group Pnma ), which is a promising high-voltage cathode material for Li-ion batteries. In contrast, comparably little is known about its metastable Pna 2 1 modification. Herein, we present a comprehensive study on the structure–property relationships of 15–20 nm Pna 2 1 -LiCoPO 4 nanospheres prepared by a simple microwave-assisted solvothermal process. Unlike previous reports, the results indicate that the compound is non-stoichiometric and shows cation-mixing with Co ions on the Li sites, which provides an explanation for the poor electrochemical performance. Co L 2,3 -edge X-ray absorption spectroscopic data confirm the local tetrahedral symmetry of Co 2+ . Comprehensive studies on the thermal stability using thermogravimetric analysis, differential scanning calorimetry, and in situ powder X-ray diffraction show an exothermic phase transition to olivine Pnma -LiCoPO 4 at 527 °C. The influence of the atmosphere and the particle size on the thermal stability is also investigated.

High-performance particles of the high-voltage cathode material LiCoPO 4 for Li-ion batteries are synthesized by a simple and rapid one-step microwave-assisted solvothermal route at moderate temperatures (250 °C). Using a variety of water/alcohol 1:1 (v:v) solvent mixtures, including ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (TTEG), polyethylene glycol 400 (PEG), and benzyl alcohol (BA), the focus of the study is set on optimizing the electrochemical performance of the material by controlling the particle size and morphology. Scanning electron microscopy studies reveal a strong influence of the co-solvent on the particle size and morphology, resulting in the formation of variations between square, rhombic and hexagonal platelets. According to selected area electron diffraction experiments, the smallest crystal dimension is in the [010] direction for all materials, which is along the lithium diffusion pathways of the olivine crystal structure. The anisotropic crystal orientations with enhanced Li-ion diffusion properties result in high initial discharge capacities and gravimetric energy densities (up to 141 mAh g −1 at 0.1 C and 677 Wh kg −1 for LiCoPO 4 obtained from TEG), excellent rate capabilities, and cycle life for 20 cycles.

Few-layer black phosphorus or phosphorene is an intriguing and important 2D material. It is a single-layer material that consists of corrugated and condensed six-membered phosphorus rings (Fig. 1). Each phosphorene layer can be weakly bonded to neighboring ones by van der Waals-like interactions to form few-layer arrangements, which are also called phosphorene in many publications. Finally, attaching many phosphorene layers to each other ends up as orthorhombic black phosphorus, a long-known phosphorus allotrope. There are two different few-layer 2D materials of phosphorus known to date, which can be derived from the element structures of orthorhombic black phosphorus (1) or gray arsenic (2). The latter is discussed as blue phosphorus in the literature (3). Since 2014, when few-layer black phosphorus was first prepared by a top-down approach from black phosphorus and used as field effect transistors (4⇓–6), a continuously increasing interest can be observed for this 2D material. Recently, an elegant, well-defined, and controllable bottom-up route for partially oxidized phosphorene ( po- phosphorene) was reported (7). In a one-pot and also low-cost process, molecular highly reactive white phosphorus acts as starting material and ethylene diamine serves as a solvent and reaction promotor (4). In a low-temperature reaction at 100 °C, po- phosphorene can be achieved on a gram scale. Due to traces of oxygen present in the solvent or during the synthesis process, the target material is partially oxidized on the surface. This aspect may look like a disadvantage at first glance, but it has turned out to be beneficial for the long-term air and moisture stability of the final product. The report in PNAS by Tian et al. (7) on the first bottom-up synthesis of well-defined po -phosphorene is a major breakthrough in synthetic chemistry. It paves the way for the large-scale … [↵][1]1Email: tom.nilges{at}lrz.tum.de. [1]: #xref-corresp-1-1

Solids with high ion mobility are of broad interest for energy storage applications. New systems featuring low-activated ion mobility are important to improve the performance in such systems. Herein we report on a model system dealing with such improved properties. Li0.2CdP2 was synthesized from the elements, lithium as structure stabilizer and CdI2 as reaction promoters in sealed silica ampoules at 823 K. It crystallizes tetragonal, in space group I4122 (α-CdAs2 structure type), with lattice parameters a = 7.6691(8) Å, c = 4.4467(4) Å and V = 261.53(4) Å3. After 24 h of storage in air lithium ions can be removed in a spontaneous delithiation reaction resulting in Li(OH)·H2O formation on the surface of the crystals. Formed α′-CdP2 adopts the α-CdAs2 structure type. Both compounds consist of isolated cadmium atoms and helical 1∞[P−]-chains generating empty channels suitable to accommodate Li ions. The heavy atom structure was determined by X-ray diffraction methods while a full model including lithium was derived from a combined solid state NMR and quantum chemical calculation approach. An low activation barrier range in the order of 0.1 to 0.2 eV was determined by NMR spectroscopy pointing towards an extraordinary high Li mobility in Li0.2CdP2. Of course a Cd-based solid will have certain disadvantages like toxicity and mass for storage applications but substitution of Cd by suitable lighter elements can solve this issue., Open Access Komponente aus der Allianzlizenz

Two-dimensional (2D) layered materials with diverse properties have attracted significant interest in the past decade. The layered materials discovered so far have covered a wide, yet discontinuous electromagnetic spectral range from semimetallic graphene, insulating boron nitride, to semiconductors with bandgaps from middle infrared to visible light. Here, we introduce new layered semiconductors, black arsenic-phosphorus (b-AsP), with highly tunable chemical compositions and electronic and optical properties. Transport and infrared absorption studies demonstrate the semiconducting nature of b-AsP with tunable bandgaps, ranging from 0.3 to 0.15 eV. These bandgaps fall into long-wavelength infrared (LWIR) regime and cannot be readily reached by other layered materials. Moreover, polarization-resolved infrared absorption and Raman studies reveal in-plane anisotropic properties of b-AsP. This family of layered b-AsP materials extend the electromagnetic spectra covered by 2D layered materials to the LWIR regime, and may find unique applications for future all 2D layered material based devices., 31 pages, 13 figures (4 in main text and 9 in Supporting Information), 2 Tables. To appear in Advanced Materials, 2015

Black phosphorus (BP) has been recently rediscovered as an elemental two-dimensional (2D) material that shows promising results for next generation electronics and optoelectronics because of its intrinsically superior carrier mobility and small direct band gap. In various 2D field-effect transistors (FETs), the choice of metal contacts is vital to the device performance, and it is a major challenge to reach ultralow contact resistances for highly scaled 2D FETs. Here, we experimentally show the effect of a work function tunable metal contact on the device performance of BP FETs. Using palladium (Pd) as the contact material, we employed the reaction between Pd and H2 to form a Pd–H alloy that effectively increased the work function of Pd and reduced the Schottky barrier height (ΦB) in a BP FET. When the Pd-contacted BP FET was exposed to 5% hydrogen concentrated Ar, the contact resistance (Rc) improved between the Pd electrodes and BP from ∼7.10 to ∼1.05 Ω·mm, surpassing all previously reported contact res...

Black arsenic phosphorus–based photodetectors sense detect long-wave mid-infrared light with high detectivity at room temperature., The mid-infrared (MIR) spectral range, pertaining to important applications, such as molecular “fingerprint” imaging, remote sensing, free space telecommunication, and optical radar, is of particular scientific interest and technological importance. However, state-of-the-art materials for MIR detection are limited by intrinsic noise and inconvenient fabrication processes, resulting in high-cost photodetectors requiring cryogenic operation. We report black arsenic phosphorus–based long-wavelength IR photodetectors, with room temperature operation up to 8.2 μm, entering the second MIR atmospheric transmission window. Combined with a van der Waals heterojunction, room temperature–specific detectivity higher than 4.9 × 109 Jones was obtained in the 3- to 5-μm range. The photodetector works in a zero-bias photovoltaic mode, enabling fast photoresponse and low dark noise. Our van der Waals heterojunction photodetectors not only exemplify black arsenic phosphorus as a promising candidate for MIR optoelectronic applications but also pave the way for a general strategy to suppress 1/f noise in photonic devices.

Particle size-tuned platelets of the high-voltage cathode material LiCoPO4 for Li-ion batteries have been synthesized by a simple one-step microwave-assisted solvothermal process using an array of water/ethylene glycol (EG) solvent mixtures. Particle size control was achieved by altering the concentration of the EG co-solvent in the mixture between 0 and 100vol%, with amounts of 0–80vol% EG producing single phase, olivine-type LiCoPO4. The particle sizes of the olivine materials were significantly reduced from about 1.2μm×1.2μm×500nm (0 vol% EG) to 200nm×100nm×50nm (80 vol% EG) with increasing EG content, while specific surface areas increased from 2 to 13m2g-1. The particle size reduction could mainly be attributed to the modified viscosities of the solvent blends. Owing to the soft template effect of EG, the crystals exhibited the smallest dimensions along the [010] direction of the Li diffusion pathways in the olivine crystal structure, resulting in enhanced lithium diffusion properties. The relationship between the synthesis, crystal properties and electrochemical performance was further elucidated, indicating that the electrochemical performances of the as-prepared materials mainly depend on the solvent composition and the respective particle size range. LiCoPO4 products obtained from reaction media with low and high EG contents exhibited good electrochemical performances (initial discharge capacities of 87–124mAhg−1at 0.1C), whereas materials made from medium EG concentrations (40–60vol% EG) showed the highest capacities and gravimetric energy densities (up to 137 mAhg−1 and 658Whkg−1at 0.1C), excellent rate capabilities, and cycle life.

A solid state melting and annealing route was used to prepare Cu6Te3S, a copper telluride sulfide representing a filled variant of the Cr3Si structure type. The title compound exhibits a reversible phase transition at 404 K which was confirmed by thermal analysis, temperature dependent X-ray single crystal and powder diffractometry. Both polymorphs crystalize cubic in space groups P 4 ¯ 3 n $P\bar 43n$ and P213, respectively. X-ray photoelectron spectroscopy (XPS) was performed to evaluate the electronic structure of Cu6Te3S and to determine the oxidation state of Cu in the title compound.

SnIP is the first atomic-scale double helical semiconductor featuring a 1.86 eV bandgap, high structural and mechanical flexibility, and reasonable thermal stability up to 600 K. It is accessible on a gram scale and consists of a racemic mixture of right- and left-handed double helices composed by [SnI] and [P] helices. SnIP nanorods

Materials with high dynamics in the solid state are of potential interest in semiconductor science and for a great variety of energy applications. In most of the cases the majority of physical properties of such compounds are directly related to their electronic structure. Optimization of properties is therefore correlated with direct or indirect control of this parameter. Compounds with highly mobile ions like the coinage metal cations and the heavy chalcogenide anions can easily be modified chemically or physically to fine tune their electronic structures. The range of adjustable properties lasts from ion conductivity, magneto resistance, thermoelectricity to a reversible redox-driven switch of semiconductivity. Today, the strong demand on clean energy production, the efficient energy transport and energy storage is a major goal for present and oncoming generations. Stable, mixed-conducting materials will play a major role in this process. The ongoing development of coinage metal chalcogenide halides during the last 50 years reflects the fundamental interest in this field. Many interesting and sometimes unexpected properties have been determined recently which substantiates the great potential of this class of materials. Especially the new class of coinage metal polychalcogenide halides is of potential interest due to their drastic modulations of physical properties driven by a fundamental tuning of its electronic structures. Thermopower and thermal diffusivity, two major properties to tune thermoelectricity can be varied in such a way that drastic changes can be addressed in very small temperature ranges close to room temperature. Herein we report on the recent progress of polychalcogenide and chalcogenide halides with the mobile d 10 ions Ag and Cu putting the main focus on silver compounds.

New ternary phosphides Ce 3 Zn 2− x P 4 and Ce 4 Zn 2− x P 5 were synthesized from intermetallic precursors CeZn and CeZn 3 , cerium, and phosphorus in equimolar NaCl/KCl fluxes. The structures were refined on the basis of single crystal X-ray diffractometer data: La 3 Zn 2 P 4 type, R 3 ¯ m , a = 414.1(1), c = 4102(1) pm, wR 2 = 0.0378, 288 F 2 values, 17 variables for Ce 3 Zn 1.82 P 4 and P 3 ¯ m 1 , a = 415.9(1), c = 1710.5(6) pm, w R 2 = 0.0408, 361 F 2 values, 20 variables for Ce 4 Zn 1.80 P 5 (new structure type). The phosphorus atoms in both structures form close-packed layers with stacking sequences ( hhcc ) 3 for Ce 3 Zn 1.82 P 4 and hhccc for Ce 4 Zn 1.80 P 5 . The cerium and zinc atoms fill octahedral and tetrahedral voids in the close-packed phosphide substructures with Ce–P and Zn–P distances in the ranges 291–302 and 249–251 pm. Temperature-dependent susceptibility measurements of Ce 4 Zn 1.80 P 5 show an experimental magnetic moment of 2.55(1) μ B /Ce atom, indicating pure trivalent cerium. Ce 4 Zn 1.80 P 5 orders antiferromagnetically at 3.5(1) K.

Systematic examinations for new phases on the quasi-binary section AgX−Ag2Q (with X = halide and Q = chalcogenide) led to the exploration of the three new compounds Ag19Te6Br7, Ag19Te6Br5.4I1.6, and Ag19Te5SeBr7. All of them crystallize in new structure types with rigid anion and highly disordered silver substructures. A peritectic decomposition to the binary halides and chalcogenides and Ag23Te12Br was observed for each compound between 693 and 719 K. Polymorphism, a common feature for solid state ion conductors, was found for Ag19Te6Br7. Impedance spectroscopic investigations showed high conductivities (up to σ = 1.1 × 10 −2 Ω−1 cm−1, 323 K, Ag19Te6Br5.4I1.6) and low activation energies (Ea = 0.19 eV, α-Ag19Te6Br7) at room temperature. A topological description of the rigid and complex anion substructure was used to classify the three different structures. Linearly arranged nets of anions, separated from each other by the disordered silver ions, corrugate under partial substitution of either the halide ...

Ag10Te4Br3 is polymorphic with four polymorphs in the temperature range from 3 to 450 K. It represents the first member of a formerly unseen class of materials featuring covalently and ionically bo...

LiCoPO4 (LCP) exists in three different structural modifications: LCP-Pnma (olivine structure), LCP-Pn21a (KNiPO4 structure type), and LCP-Cmcm (Na2CrO4 structure type). The synthesis of the LCP-Cmcm polymorph has been reported via high pressure/temperature solid-state methods and by microwave-assisted solvothermal synthesis. Phase transitions from both LCP-Pn21a and LCP-Cmcm to LCP-Pnma upon heating indicates a metastable behavior. However, a precise study of the structural changes during the heating process and the magnetic properties of LCP-Cmcm are hitherto unknown. Herein, we present the synthesis and characterization of LCP-Cmcm via a rapid and facile soft-chemistry approach using two different kinetically controlled pathways, solvothermal and polyol syntheses, both of which only require relatively low temperatures (~200 °C). Additionally, by polyol, method a dumbbell-like morphology is obtained without the use of any additional surfactant or template. A temperature-dependent in situ powder XRD shows a transition from LCP-Cmcm at room temperature to LCP-Pnma and finally to LCP-Pn21a at 575 and 725 °C, respectively. In addition to that, the determination of the magnetic susceptibility as a function of temperature indicates a long-range antiferromagnetic order below TN = 11 K at 10 kOe and 9.1 K at 25 kOe. The magnetization curves suggests the presence of a metamagnetic transition.

Olivine-type LiCoPO4 is considered a promising high-voltage cathode material for next-generation lithium-ion batteries. However, preparing high-performance LiCoPO4 by a simple approach has been challenging. Herein, we present a facile and rapid (30 min) one-step microwave-assisted solvothermal synthesis route using a 1 : 1 (v/v) water/ethylene glycol (EG) binary solvent mixture and a temperature of 250 °C. The technique delivers high-performance LiCoPO4 nanoparticles without additional post-annealing or carbon coating steps. The as-prepared powder consists of single crystalline LiCoPO4 and features a hexagonal platelet-like morphology with dimensions of 700–800 nm × 400–600 nm × 100–220 nm. Selected area electron diffraction (SAED) experiments reveal that the platelets show the smallest dimension along [010], which is the direction of the lithium diffusion pathways in the olivine crystal structure. Furthermore, the results indicate that the EG co-solvent plays an important role in tailoring the particle size, morphology, and crystal orientation of the material. Co L-edge soft X-ray absorption spectroscopy (XAS) of LiCoPO4 are presented for the first time and confirm that the material only consists of Co2+. Benefiting from the unique morphology, which facilitates Li-ion conduction, electrochemical measurements deliver an initial discharge capacity of 137 mA h g−1 at 0.1 C, a remarkably stable capacity retention of 68% after 100 cycles at 0.5 C, and a specific energy density of 658 W h kg−1 based on its capacity and voltage, which is the best performance of LiCoPO4 obtained from microwave-assisted solvothermal synthesis to date.

Ag10Te4Br3 is the first representative of an M(group 11) (poly)chalcogenide halide with covalently bonded [Te2]2- units and isolated Te2- ions. It represents a new class of materials located between M(group 11) chalcogen halides, characterized by covalently bonded chalcogen structure motives, on the one hand and chalcogenide halides, consisting of isolated chalcogenide ions, on the other. A high silver mobility on distinct silver layers was observed for orthorhombic Ag10Te4Br3, resulting in a pronounced 1D silver mobility at room temperature. The covalent regions of the chalcogen substructure account for the lowest activation energies, determined after a detailed analysis of the silver joint probability density functions (jpdf). Impedance spectroscopic measurements were performed in order to substantiate the results from jpdf analyses. Ag10Te4Br3 is an excellent conductor, with conductivities on the same order of magnitude as β-Ag3SX (X = I, Br) or glassy silver chalcogenide halides. The occurrence of the...

Herein we report the structural, thermal and physical properties of Ag5Te2−ySeyCl ( y = 0 –0.7). Polymorphic Ag5Te2Cl ( y = 0 ) is an ion conductor with two reversible phase transitions at 241 and 334 K. While the monoclinic room temperature β- and the low temperature γ-phase show conductivities below σ = 10 −3 Ω −1 cm −1 , the tetragonal high temperature α-phase is a promising conductor for electronic devices with conductivities up to 10 −1 Ω −1 cm −1 in addition to high moisture and photo stability. The α–β-phase transition temperature of ion conducting Ag5Te2Cl can be lowered by partial substitution of tellurium by selenium. From differential thermal analysis (DTA) and differential scanning calorimetry (DSC) a linear decrease of the α–β-phase transition temperature with increasing compositional parameter y to a minimum transition temperature of 239 K was observed for Ag5Te1.3Se0.7Cl. Phases up to a maximum selenium content of y = 0.7 were stabilized by preservation of the β- and α-Ag5Te2Cl structure types. Ag5Te2−ySeyCl ( y = 0 –0.9) phases were characterised by powder X-ray diffraction (XRD) at room temperature. The stabilization of the α-Ag5Te2Cl structure type in Ag5Te2−ySeyCl around room temperature results in an increase of conductivity of more than 2 orders of magnitude compared to the ternary phase. Conductivity of up to σ = 5.1 × 10 −2 Ω −1 cm −1 (314 K, α-Ag5Te1.6Se0.4Cl) was observed by impedance spectroscopy. In the range from room temperature down to 239 K any transition temperature can be chosen by simply varying the composition.

Single crystals of orthorhombic black phosphorus can be grown by a short way transport reaction from red phosphorus and Sn/SnI4 as mineralization additive. Sizes of several millimeters can be realized with high crystal quality and purity, making a large area preparation of single or multilayer phosphorene possible. An in situ neutron diffraction study has been performed addressing the formation of black phosphorus. Black phosphorus is formed directly via gas phase without the occurrence of any other intermediate phase. Crystal growth was initiated after cooling the starting materials down from elevated temperatures at 500 {\deg}C., Comment: 12 Pages, 6 Figures

International audience; Recently silver(I)-(poly)chalcogenides have received special interest in energy conversion materials because of their thermoelectric and resistivity switching properties. In order to understand these features, a new topological principle has been developed, which is an useful tool to plan new synthesis strategies and to vary functional properties. It has been shown that anion substitution is powerful tool to tune the physical properties in terms of a thermoelectric performance optimization. Herein we report on the recently introduced substance class of silver(I)-(poly)chalcogenidehalides and the well-established class of silver(I)-chalcogenidehalides. We focus our report on the electrochemical behaviour of all known silver-(poly)telluridehalides Ag10Te4Br3, Ag23Te12Br, Ag20Te10BrI,Ag5Te2Cl and selected substituted phases.

Semiconductors are key materials in modern electronics and are widely used to build, for instance, transistors in integrated circuits as well as thermoelectric materials for energy conversion, and there is a tremendous interest in the development and improvement of novel materials and technologies to increase the performance of electronic devices and thermoelectrics. Tetramorphic Ag10Te4Br3 is a semiconductor capable of switching its electrical properties by a simple change of temperature. The combination of high silver mobility, a small non-stoichiometry range and an internal redox process in the tellurium substructure causes a thermopower drop of 1,400 μV K−1, in addition to a thermal diffusivity in the range of organic polymers. The capability to reversibly switch semiconducting properties from ionic to electronic conduction in one single compound simply by virtue of temperature enables novel electronic devices such as semiconductor switches. Switching between n- and p-type conduction in a semiconductor can be done through doping. A fundamentally different behaviour has now been observed in Ag10Te4Br3, as a transition from ionic to electronic conduction is achieved simply by heating, which could be used for switches or in novel electronic devices.

Compared to the hitherto known polymeric seleno- and perselenoborates a new and remarkable structural principle was realized in the lithium selenoborate Li7B7Se15. The three dimensional anion sublattice is formed by entities of formal composition [B7Se13]5−. Additionally, isolated diselenide units and lithium cations are found in the structure. The connection pattern of the basic corner-sharing BSe4-tetrahedra gives rise to this tetragonal structure hitherto unknown in both, oxidic and non-oxidic chalcogenoborate chemistry. A characteristic feature of the structure is an extensive system of channels facilitating ionic motion and providing different diffusion paths for the Li ions. This channel system offers several atom sites suitable for lithium cations. As expected, some Li positions are partially occupied and they show comparatively large anisotropic displacement ellipsoids which prove the mobility of the cations already at room temperature, indicating an above average ion conductivity in this chalcogenoborate. The new chalcogenoborate was prepared in a solid state reaction from lithium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 800 °C. Li7B7Se15 crystallizes tetragonal, space group P 4 2 / n b c (no. 133) with a = 11.4107 ( 4 ) A , c = 16.4251 ( 5 ) A at 273 K, and Z = 4 . JPDF-calculations based on the displacement parameters using a non harmonic approach and 6Li magic-angle spinning (MAS) NMR spectra at 210 K yield resolved resonances for the Li(1) site and a dynamically averaged Li(2,3) site. The site populations deduced from NMR and X-ray diffraction are found in excellent agreement with each other. Line broadening and coalescence phenomena observed within the temperature region 240 K ⩽ T ⩽ 300 K reveal thermally activated ion transfer between the Li(1) ↔ Li(2,3) sites, which can be simulated well by standard two-site exchange theory. From the temperature dependent motional correlation times we extract an activation energy of 59(1) kJ/mole for this process.

By tailoring the architecture of a bulk material at several different length scales, the ability of a semiconductor to convert heat into voltage has been optimized to a groundbreaking level of performance. See Letter p.414 Thermoelectric materials offer ways to transform heat to electrical energy and vice versa. Here, the authors tailor the architecture of a bulk thermoelectric material, the semiconductor lead telluride, to maximize thermoelectric performance. They achieve phonon scattering on three different length scales. Atomic-scale doping, nanometer-scale endotaxial precipitation and mesoscale grain-boundary structures were introduced to the material to drastically reduce its thermal conductivity and subsequently achieve a very high thermoelectric figure of merit. These advances could aid in the design of advanced thermoelectric materials that can be used to recover waste heat.

In recently years, scientific research has been focused on finding new sources of efficient energy storage and lithium batteries are one of the most outstanding alternatives. Nowadays, investigation on cathode materials constitute one of the key factors of lithium rechargeable batteries studies. Recently, oxides with olivine structures has triggered the battery field, due to its excellent electrochemical properties, crystal stability, energy density, power capacity and are not expensive. However, the demand and development of more enhanced cathode materials can be achieved by the use of sophisticated synthetic methods. The purpose of this article is to provide a perspective to the materials community on the opportunities and limitations of nanostructured materials by highlighting examples in synthesis, fundamental studies and applications on microwave synthesis as novel route to obtain high voltage phospho-olivines.

Black phosphorus prepared via the mineralization concept displays promising characteristics with respect to Li-ion battery applications. Although the theoretical specific capacity of black phosphorus as a negative electrode material is 2596 mA h g−1, a good cycling stability at high capacities, however, is still missing. Even worse, a large capacity drop after the first cycle is present and, depending on the electrode preparation, a poor first cycle coulombic efficiency (only 8%) represents a huge challenge to overcome. Herein we report on the performances of black phosphorus as a negative electrode material and display the roles of Cu3P and the copper current collector in this context. Furthermore, a composite material prepared by reacting pristine black phosphorus particles with a copper solution under solvothermal conditions shows a first cycle coulombic efficiency of 43%. We show that the presence of copper is crucial for the electrochemical performance of black phosphorus and that also the particle size and the electrode preparation procedure play a crucial role.

Electrochemical energy storage devices such as lithium ion batteries (LIBs), sodium-ion batteries (NIBs) and supercapacitors (SCs) have been developed for various potential applications including portable electronics, electro-mobility, and large-scale stationary energy storage. This thesis focuses on developing novel polyoxometalates (POMs) and nanostructured carbon materials as electrode materials for SCs, LIBs, and NIBs, as well as investigating respective their charge storage/transport mechanism. A polyoxovanadate, Na6[V10O28], is synthesized using a simple solution process, and studied as electrode materials for SCs and LIBs in this thesis. The electrochemical properties of Na6[V10O28] electrodes for SCs are investigated in Li-ion containing organic electrolyte utilizing galvanostatic charge/discharge and cyclic voltammetry in a three-electrode configuration. Activated carbon (AC) is employed as the positive electrode to assemble an asymmetric supercapacitor with Na6[V10O28] as the negative electrode in order to demonstrate that Na6[V10O28] is a promising electrode material for practical supercapacitor applications. The electrochemical properties of Na6[V10O28] as a cathode in LIBs is also tested by galvanostatic charge/discharge and cyclic voltammetry in a half-cell configuration, and exhibits a high capacity (up to 213 mAh g−1). In order to figure out the charge storage and transport mechanism, in-situ V K-edge X-ray absorption fine structure (XAFS) measurements and temperature dependent Chronoamperometry measurements are utilized for Na6[V10O28] LIBs. Those techniques can detect the oxidation states and inner structure changes of Na6[V10O28] during charging/discharging, as well as determine the rate of electron transfer and the reorganization energy of Na6[V10O28] electrodes. A POM/Carbon hybrid material is also investigated in this thesis for SC applications. A nanohybrid material which combines (TBA)5[PVV2MoVI10O40] (TBA-PV2Mo10, TBA: [(CH3(CH2)3)4N]+, tetra-n-butyl ammonium) and single-walled carbon nanotubes (SWCNTs) is synthesized by a simple solution method which electrostatically attaches anionic [PV2Mo10O40]5- anions with organic TBA cations on the SWCNTs. SWCNT-TBA-PV2Mo10 electrodes is tested in an acidic aqueous electrolyte by galvanostatic charge/discharge and cyclic voltammetry in three-electrode-configuration in order to figure out the electrochemical performance. In this SWCNT-TBA-PV2Mo10 nanohybrid material, TBA-PV2Mo10 offers redox activity while the TBA organic groups help to preventing dissolution in the aqueous electrolyte in order to increase the cycling stability, and SWCNTs offers high electrical conductivity with high double-layer capacitance that improve both energy and power density. A SWCNT-TBA-PV2Mo10 symmetric SC is fabricated and exhibits a 39 % higher specific capacitance as compared to a SWCNT symmetric SC, and presents high cycling stability up to 6500 cycles. A nanostructured carbon material, core–shell heterostructure with multi-walled carbon nanotubes (MWCNTs) as the core and graphene oxide nanoribbons (GONRs) as the shell (MWCNT@GONR), is also investigated as anode material for NIBs in this thesis. MWCNT@GONR with oxygen-containing functional groups is synthesized by unzipping process of MWCNTs utilizing microwave-assisted process. Annealing process is employed to study the influence of the amount of carboxylic acid groups on the electrochemistry of MWCNT@GONR. The novel core-shell structure prevents the restacking problem of graphene and enables penetration of the electrolyte. Furthermore, MWCNTs offer high electronic conductivity and direct electron transfer path while GONRs offer high surface area and functional groups which adsorb more Na ions on the surface therefore increasing capacity. A full cell which combines MWCNT@GONR as anode and P2-NaxMnO2 as cathode is assembled and exhibits a high energy density. Doctor of Philosophy