Diffusion of Macromolecules across the Nuclear Pore Complex

Nuclear pore complexes (NPCs) are very selective filters that monitor the transport between the cytoplasm and the nucleoplasm. Two models have been suggested for the plug of the NPC. They are (i) it is a reversible hydrogel or (ii) it is a polymer brush. We propose a mesoscopic model for the transport of a protein through the plug, that is general enough to cover both. The protein stretches the plug and creates a local deformation. The bubble so created (prtoein+deformation) executes random walk in the plug. We find that for faster relaxation of the gel, the diffusion of the bubble is greater. Further, on using parameters appropriate for the brush, we find that the diffusion coefficient is much lower. Hence the gel model seems to be more likely explanation for the workings of the plug

<i>n</i>‑Type Ultrathin Few-Layer Nanosheets of Bi-Doped SnSe: Synthesis and Thermoelectric Properties

SnSe, an environmentally friendly layered chalcogenide, has fostered immense attention in the thermoelectric community with its high thermoelectric figure of merit in single crystals. Although the stride toward developing superior <i>p</i>-type SnSe as a thermoelectric material is progressing rapidly, synthesis of <i>n</i>-type SnSe is somewhat overlooked. Here, we report the solution-phase synthesis and thermoelectric transport properties of two-dimensional (2D) ultrathin (1.2–3 nm thick) few-layer nanosheets (2–4 layers) of <i>n</i>-type SnSe. The <i>n</i>-type nature of the nanosheets initially originates from chlorination of the material during the synthesis. We could increase the carrier concentration of <i>n</i>-type SnSe significantly from 3.08 × 10¹⁷ to 1.97 × 10¹⁸ cm^–3 via further Bi doping, which results in an increase of electrical conductivity and power factor. Furthermore, Bi-doped nanosheets exhibit ultralow lattice thermal conductivity (∼0.3 W/mK) throughout the temperature range of 300–720 K, which can be ascribed to the effective phonon scattering by an interface of SnSe layers, nanoscale grain boundaries, and point defects

Insights into the Lithium Substructure of the Superionic Conductors Li3YCl6 and Li3YBr6

The recent interest in the halide-based solid electrolytes Li3MX6 (M = Y, Er, In; X = Cl, Br, I) shows these materials to be promising candidates for solid-state battery application, due to high ionic conductivity and large electrochemical stability window. However, almost nothing is known about the underlying lithium sub-structure within those compounds. Here, we investigate the lithium sub-structure of Li3YCl6 and Li3YBr6 using temperature-dependent neutron diffraction. We compare compounds prepared by classic solid-state syntheses with a mechanochemical synthesis to shed light on the influence of the synthetic approach on the reported yttrium disorder and the resulting surrounding lithium sub-structure. This work provides a better understanding of the strong differences in ionic transport depending on the synthesis procedure of Li3MX6

Local ferroelectricity in thermoelectric SnTe above room temperature driven by competing phonon instabilities and soft resonant bonding

We report direct observation of local ferroelectric ordering above room temperature in rocksalt SnTe, which is a topological crystalline insulator and a good thermoelectric material. Although SnTe is known to stabilize in a ferroelectric ground state (rhombohedral phase) below ∼100 K, at high temperatures it was not expected to show any ferroelectric ordering forbidden by its globally centro-symmetric crystal structure (Fm-3m). Here, we show that SnTe exhibits local ferroelectric ordering that is robust above room temperature through direct imaging of ferroelectric domains by piezoresponse force microscopy and measurement of local polarization switching using switching spectroscopy. Using first-principles theoretical analysis, we show how the local ferroelectricity arises from soft bonding and competing phonon instabilities at intermediate wavelengths, which induce local Sn-off centering in the otherwise cetrosymmetric SnTe crystal structure. The results make SnTe an important member of the family of new multi-functional materials namely the ferroelectric-thermoelectrics

On the underestimated influence of synthetic conditions in solid ionic conductors

The development of high-performance inorganic solid electrolytes is central to achieving high-energy- density solid-state batteries. Whereas these solid-state materials are often prepared via classic solid-state syntheses, recent efforts in the community have shown that mechanochemical reactions, solution syntheses, microwave syntheses, and various post-synthetic heat treatment routines can drastically affect the structure and microstructure, and with it, the transport properties of the materials. On the one hand, these are important considerations for the upscaling of a materials processing route for industrial applications and industrial production. On the other hand, it shows that the influence of the different syntheses on the materials' properties is neither well understood fundamentally nor broadly internalized well. Here we aim to review the recent efforts on understanding the influence of the synthetic procedure on the synthesis-(micro)structure-transport correlations in superionic conductors. Our aim is to provide the field of solid-state research a direction for future efforts to better understand current materials properties based on synthetic routes, rather than having an overly simplistic idea of any given composition having an intrinsic conductivity. We hope this review will shed light on the underestimated influence of synthesis on the transport properties of solid electrolytes toward the design of syntheses of future solid electrolytes and help guide industrial efforts of known materials.</p

Understanding the Chemical Nature of the Buried Nanostructures in Low Thermal Conductive Sb-Doped SnTe by Variable-Energy Photoelectron Spectroscopy

Nanoprecipitates embedded in a matrix of thermoelectric materials decrease the lattice thermal conductivity significantly by extensive heat carrying phonon scattering. Recently, two-dimensional layered intergrowth nanostructures of Sn$_m$Sb$_{2n}$Te$_{3n+m}$ embedded in SnTe matrix have provided record low lattice thermal conductivity in SnTe, but an understanding of the chemical nature of these layered nanostructures is still not clear. Herein, we studied the chemical nature of the intergrowth nanostructures of a series Sb-doped SnTe by variable-energy X-ray photoelectron spectroscopy at synchrotron, which is well known to probe buried interfaces and embedded nanostructures. The primary oxidation states of Sb, Sn, and Te in these intergrowth structures are found to be in +3, +2, and −2, respectively, which is expected from the composition. However, both the Sn and Sb are found to be slightly oxidized in the surface. From the intensity variation with photon energy, we have found a thin layer of SnO$_2$ (∼4.5 nm) on the sample surfaces and the thickness decreases with Sb doping. Te is also found in 0 oxidation states, which corroborates with the variation of Sn vacancies with Sb doping. The valence band features near the edge do not change significantly with Sb doping. This understanding of the chemical nature of low lattice thermal conductive Sb-doped SnTe will help further to design the thermoelectric materials with their surface phenomenon

Mechanochemical Synthesis: A Tool to Tune Cation Site Disorder and Ionic Transport Properties of Li 3

The lithium-conducting, rare-earth halides, Li₃MX₆ (M = Y, Er; X = Cl, Br), have garnered significantly rising interest recently, as they have been reported to have oxidative stability and high ionic conductivities. However, while a multitude of materials exhibit a superionic conductivity close to 1 mS cm⁻¹, the exact design strategies to further improve the ionic transport properties have not been established yet. Here, the influence of the employed synthesis method of mechanochemical milling, compared to subsequent crystallization routines as well as classic solid-state syntheses on the structure and resulting transport behavior of Li₃ErCl₆ and Li₃YCl₆ are explored. Using a combination of X-ray diffraction, pair distribution function analysis, density functional theory, and impedance spectroscopy, insights into the average and local structural features that influence the underlying transport are provided. The existence of a cation defect within the structure in which Er/Y are disordered to a new position strongly benefits the transport properties. A synthetically tuned, increasing degree of this disordering leads to a decreasing activation energy and increasing ionic conductivity. This work sheds light on the possible synthesis strategies and helps to systematically understand and further improve the properties of this class of materials

Mechanochemical Synthesis: A Tool to Tune Cation Site Disorder and Ionic Transport Properties of Li3MCl6(M = Y, Er) Superionic Conductors

The lithium-conducting, rare-earth halides, Li₃MX₆ (M = Y, Er; X = Cl, Br), have garnered significantly rising interest recently, as they have been reported to have oxidative stability and high ionic conductivities. However, while a multitude of materials exhibit a superionic conductivity close to 1 mS cm⁻¹, the exact design strategies to further improve the ionic transport properties have not been established yet. Here, the influence of the employed synthesis method of mechanochemical milling, compared to subsequent crystallization routines as well as classic solid-state syntheses on the structure and resulting transport behavior of Li₃ErCl₆ and Li₃YCl₆ are explored. Using a combination of X-ray diffraction, pair distribution function analysis, density functional theory, and impedance spectroscopy, insights into the average and local structural features that influence the underlying transport are provided. The existence of a cation defect within the structure in which Er/Y are disordered to a new position strongly benefits the transport properties. A synthetically tuned, increasing degree of this disordering leads to a decreasing activation energy and increasing ionic conductivity. This work sheds light on the possible synthesis strategies and helps to systematically understand and further improve the properties of this class of materials