Highly stabilized and efficient thermoelectric copper selenide.

The liquid-like feature of thermoelectric superionic conductors is a double-edged sword: the long-range migration of ions hinders the phonon transport, but their directional segregation greatly impairs the service stability. We report the synergetic enhancement in figure of merit (ZT) and stability in Cu1.99Se-based superionic conductors enabled by ion confinement effects. Guided by density functional theory and nudged elastic band simulations, we elevated the activation energy to restrict ion migrations through a cation-anion co-doping strategy. We reduced the carrier concentration without sacrificing the low thermal conductivity, obtaining a ZT of ∼3.0 at 1,050 K. Notably, the fabricated device module maintained a high conversion efficiency of up to ∼13.4% for a temperature difference of 518 K without obvious degradation after 120 cycles. Our work could be generalized to develop electrically and thermally robust functional materials with ionic migration characteristics.

Prominent Josephson tunneling between twisted single copper oxide planes of Bi2Sr2-xLaxCuO6+y.

Josephson tunneling in twisted cuprate junctions provides a litmus test for the pairing symmetry, which is fundamental for understanding the microscopic mechanism of high temperature superconductivity. This issue is rekindled by experimental advances in van der Waals stacking and the proposal of an emergent d+id-wave. So far, all experiments have been carried out on Bi2Sr2CaCu2O8+x (Bi-2212) with double CuO2 planes but show controversial results. Here, we investigate junctions made of Bi2Sr2-xLaxCuO6+y (Bi-2201) with single CuO2 planes. Our on-site cold stacking technique ensures uncompromised crystalline quality and stoichiometry at the interface. Junctions with carefully calibrated twist angles around 45° show strong Josephson tunneling and conventional temperature dependence. Furthermore, we observe standard Fraunhofer diffraction patterns and integer Fiske steps in a junction with a twist angle of 45.0±0.2°. Together, these results pose strong constraints on the d or d+id-wave pairing and suggest an indispensable isotropic pairing component.

Correlating the charge-transfer gap to the maximum transition temperature in Bi2Sr2Can-1CunO2n+4+δ.

As the number of CuO2 layers, n, in each unit cell of a cuprate family increases, the maximum transition temperature (Tc,max) exhibits a universal bell-shaped curve with a peak at n = 3. The microscopic mechanism of this trend remains elusive. In this study, we used advanced electron microscopy to image the atomic structure of cuprates in the Bi2Sr2Can-1CunO2n+4+δ family with 1 ≤ n ≤ 9; the evolution of the charge-transfer gap size (Δ) with n can be measured simultaneously. We determined that the n dependence of Δ follows an inverted bell-shaped curve with the minimum Δ value at n = 3. The correlation between Δ, n, and Tc,max may clarify the origin of superconductivity in cuprates.

Silver-Catalyzed Synthesis of Benzyl Ethers via Alkoxylation of Benzylic C(sp3 )-H Bonds.

Alkoxylation of benzylic C(sp3 )-H bonds has become one of the most important tools for the construction of benzyl ethers from feedstock chemicals. Herein, we reported a silver catalyzed alkoxylation of benzylic C(sp3 )-H bonds employing potassium persulfate as an oxidant at room temperature. This strategy showed good functional-group tolerance, site selectivity, and chemoselectivity. The reaction proceeded smoothly in the presence of various primary, secondary, and tertiary alcohol nucleophiles, affording corresponding benzyl ethers. Combined experimental studies provided mechanistic insights into the possible radical pathways. Furthermore, a possible mechanism was proposed for this method.

Topological spin texture in the pseudogap phase of a high-Tc superconductor.

An outstanding challenge in condensed-matter-physics research over the past three decades has been to understand the pseudogap (PG) phenomenon of the high-transition-temperature (high-Tc) copper oxides. A variety of experiments have indicated a symmetry-broken state below the characteristic temperature T* (refs. 1-8). Among them, although the optical study5 indicated the mesoscopic domains to be small, all these experiments lack nanometre-scale spatial resolution, and the microscopic order parameter has so far remained elusive. Here we report, to our knowledge, the first direct observation of topological spin texture in an underdoped cuprate, YBa2Cu3O6.5, in the PG state, using Lorentz transmission electron microscopy (LTEM). The spin texture features vortex-like magnetization density in the CuO2 sheets, with a relatively large length scale of about 100 nm. We identify the phase-diagram region in which the topological spin texture exists and demonstrate the ortho-II oxygen order and suitable sample thickness to be crucial for its observation by our technique. We also discuss an intriguing interplay observed among the topological spin texture, PG state, charge order and superconductivity.

When not helping is nice: Children's changing evaluations of helping during COVID-19.

A key aspect of children's moral and social understanding involves recognizing the value of helpful behaviors. COVID-19 has complicated this process; behaviors generally considered praiseworthy were considered problematic during the COVID-19 pandemic. The present study examined whether 6- to 12-year-olds (N = 228; residing in the United States) adapt their evaluations of helpful behavior in response to shifting norms. Specifically, we presented children with scenarios featuring helpful and unhelpful actions that involved physical interaction (e.g., hugging) or nonphysical interaction (e.g., recruiting a teacher); although all children were tested during the COVID-19 pandemic, stories portrayed individuals either before or during COVID-19. While children generally judged helpfulness positively and unhelpfulness negatively, children exhibited a selective shift in their judgments for COVID-19 scenarios: children considered helpfulness negatively and unhelpfulness positively if helping required physical interaction. These findings demonstrate that children flexibly tune their social evaluations of helping to align with evolving norms. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Radical Esterification of Unactivated Alkenes Using Formate as Carbonyl Source.

In recent years, methyl formate has received considerable attention as an ideal and green C1 building block to synthesize carboxylic esters. However, examples of a one-step route to esters with one-carbon elongation using methyl formate as a source of methoxycarbonyl radical are still rare. Herein, we present peroxide-induced radical carbonylation of N-(2-methylallyl)benzamides with methyl formate as the precursor of methoxycarbonyl radical and RuCl3 as catalyst, affording a series of biologically valuable 4-[(methoxycarbonyl)methyl]-3,4-dihydroisoquinolinones with good tolerance and insensitivity to moisture in one pot under simple and mild conditions.

Visible-Light-Promoted Synthesis of α-CF2H-Substituted Ketones by Radical Difluoromethylation of Enol Acetates.

An efficient and novel visible-light-promoted radical difluoromethylation of enol acetates for the synthesis of α-CF2H-substituted ketones has been described. Upon irradiation under blue LED with catalytic amounts of fac-Ir(ppy)3, this photocatalytic procedure employs difluoromethyltriphenylphosphonium bromide as a radical precursor. Various α-CF2H-substituted ketones are successfully created via designed systems based on the SET process. The methodology has also provided an operationally simple process with broad functional group compatibility.

1D/2D Heterostructures as Ultrathin Catalysts for Hydrogen Evolution Reaction.

2D MoS2 has emerged as a promising alternative to Pt-based catalysts for hydrogen evolution reaction (HER) due to its low cost and earth abundance. However, insufficient active sites of basal plane and poor conductivity become the foremost factors restricting the catalytic performance of MoS2 . Here, a facile strategy is presented to enhance the HER performance of MoS2 by converting its 2D structure into 1D/2D heterostructures of Mo6 Te6 /MoS2(1- x ) Te2 x by the in situ tellurization. As-prepared 1D/2D heterostructures exhibit excellent HER performance with the Tafel slope of ≈56 mV dec-1 (only one-third of that for pristine MoS2 ). The enhanced HER catalytic activity is attributed to more Te/S vacancies introduced by tellurization, which serve as the active sites as suggested by theoretical calculations. Besides, the formation of highly conductive well-aligned quasi-1D Mo6 Te6 nanobelts facilitate charge transport in HER. Previous work provides a facile approach to construct mixed dimensional materials, and opens up a new avenue to the properties modulation of 2D transition metal chalcogenides.

The Detection of the Pipe Crack Utilizing the Operational Modal Strain Identified from Fiber Bragg Grating.

The small and light-weight pipeline is widely used in hydraulic system for aerospace engineering. The crack is one of the most common failures in the pipelines so that its incipient detection can further avoid the catastrophic damage of the piping system. The electrical and piezoelectric sensors are conventionally used for the structural health monitoring (SHM), while these are not suitable for the cascaded pipelines in harsh environment because the added mass will change the modal characteristics of the cascaded pipelines. The Fiber Bragg Grating (FBG) sensor with light-weight, multiplexed, and anti-electromagnetic interference properties, are employed to obtain the modal strain transmissibility with a novel diagram of the operational modal analysis (OMA). Based on the OMA an enhanced damage indicator is proposed to detect the crack. After going through analytical modeling, finite element modeling (FEM) and its corresponding experiments, it is concluded that the presented method is effective and accurate to detect and locate the crack.

Langmuir-Blodgett self-assembly of ultrathin graphene quantum dot films with modulated optical properties.

Multiple-color-emissive graphene quantum dots (GQDs) have great potential in diverse applications such as bioimaging, light emission, and photocatalysis. Growing interest in GQDs is largely focused on their macro-scale aggregations that could inherit the unique properties of individual dots. However, the lack of advanced fabrication methods limits the practical applications of GQDs. Here, we employed a Langmuir-Blodgett (LB) technique to fabricate ultrathin, high-quality GQD aggregated films with well-modulated optical properties in a wide range of wavelengths. Through the combination of a bottom-up synthesis of GQDs and the LB assembly method, uniform, closely packed, and ultra-thin GQD films can be self-assembled with a well-controlled thickness on different substrates. The photoluminescence (PL) spectra of ultra-thin GQD films have an obvious red-shift compared with isolated GQD solution. We then elucidate remarkably strong energy transfer in self-assembled GQDs. Furthermore, the ultra-thin GQD films exhibit a clear excitation-dependent PL that could almost cover the entire visible light. This convenient self-assembly method and systematic optical and physical studies of ultra-thin GQD films may provide a new direction for developing low-cost, GQD film-based light-emitting devices.

Direct imaging of structural changes induced by ionic liquid gating leading to engineered three-dimensional meso-structures.

The controlled transformation of materials, both their structure and their physical properties, is key to many devices. Ionic liquid gating can induce the transformation of thin-film materials over long distances from the gated surface. Thus, the mechanism underlying this process is of considerable interest. Here we directly image, using in situ, real-time, high-resolution transmission electron microscopy, the reversible transformation between the oxygen vacancy ordered phase brownmillerite SrCoO2.5 and the oxygen ordered phase perovskite SrCoO3. We show that the phase transformation boundary moves at a velocity that is highly anisotropic, traveling at speeds ~30 times faster laterally than through the thickness of the film. Taking advantage of this anisotropy, we show that three-dimensional metallic structures such as cylinders and rings can be realized. Our results provide a roadmap to the construction of complex meso-structures from their exterior surfaces.

Selective nickel-catalyzed dehydrogenative-decarboxylative formylation of indoles with glyoxylic acid.

Herein we present a new strategy for the dehydrogenative-decarboxylative coupling of indoles with glyoxylic acid. A broad range of indoles were transformed into the corresponding 3-formylindoles in moderate to good yields and excellent functional group tolerance. Notably, no N-formylation product was detected under our conditions.

Copper-catalyzed carbonylative transformations of indoles with hexaketocyclohexane.

With hexaketocyclohexane octahydrate as the carbon monoxide source, a novel procedure for copper-catalyzed direct double carbonylation of indoles has been established. Using alcohols as reaction partners, moderate to good yields of the desired double carbonylation products have been obtained. Wide functional group tolerance and substrate scope can be observed.

Carbonylative coupling of N-chloroamines with alcohols: synthesis of esterification reagents.

Herein we report a new method for the carbonylative synthesis of carbamates. Starting from N-chloroamines and alcohols, with copper or Pd/C as the catalyst, the corresponding carbamates were produced in moderate to good yields. No additional oxidant or base is needed in this system. Notably, the produced benzotriazole-carboxylates can be used as esterification reagents.

Stable iridium dinuclear heterogeneous catalysts supported on metal-oxide substrate for solar water oxidation.

Atomically dispersed catalysts refer to substrate-supported heterogeneous catalysts featuring one or a few active metal atoms that are separated from one another. They represent an important class of materials ranging from single-atom catalysts (SACs) and nanoparticles (NPs). While SACs and NPs have been extensively reported, catalysts featuring a few atoms with well-defined structures are poorly studied. The difficulty in synthesizing such structures has been a critical challenge. Here we report a facile photochemical method that produces catalytic centers consisting of two Ir metal cations, bridged by O and stably bound to a support. Direct evidence unambiguously supporting the dinuclear nature of the catalysts anchored on α-Fe2O3 is obtained by aberration-corrected scanning transmission electron microscopy (AC-STEM). Experimental and computational results further reveal that the threefold hollow binding sites on the OH-terminated surface of α-Fe2O3 anchor the catalysts to provide outstanding stability against detachment or aggregation. The resulting catalysts exhibit high activities toward H2O photooxidation.

Atomic scale imaging of magnetic circular dichroism by achromatic electron microscopy.

In order to obtain a fundamental understanding of the interplay between charge, spin, orbital and lattice degrees of freedom in magnetic materials and to predict and control their physical properties1-3, experimental techniques are required that are capable of accessing local magnetic information with atomic-scale spatial resolution. Here, we show that a combination of electron energy-loss magnetic chiral dichroism 4 and chromatic-aberration-corrected transmission electron microscopy, which reduces the focal spread of inelastically scattered electrons by orders of magnitude when compared with the use of spherical aberration correction alone, can achieve atomic-scale imaging of magnetic circular dichroism and provide element-selective orbital and spin magnetic moments atomic plane by atomic plane. This unique capability, which we demonstrate for Sr2FeMoO6, opens the door to local atomic-level studies of spin configurations in a multitude of materials that exhibit different types of magnetic coupling, thereby contributing to a detailed understanding of the physical origins of magnetic properties of materials at the highest spatial resolution.

A copper-catalyzed carbonylative four-component reaction of ethene and aliphatic olefins.

To have a balance between reactivity and selectivity has been a long-standing challenge in multicomponent reactions. In this communication, a carbonylative four-component reaction has been developed. With copper as the catalyst, using ethene including other aliphatic alkenes, alcohols and acetonitrile as the substrates under CO pressure, various desired products were produced in moderate to good yields. The obtained products can be applied in the synthesis of δ-valerolactams. Good functional group tolerance and reaction efficiency can be observed here.

Publisher Correction: Atomic scale imaging of magnetic circular dichroism by achromatic electron microscopy.

In Fig. 1 of the version of this Letter originally published, the word 'Subtract' was missing from the green box to the left of panel f. This has now been corrected in all versions of the Letter.

Silver and Palladium Cocatalyzed Carbonylative Activation of Benzotriazoles to Benzoxazinones under Neutral Conditions.

A novel and efficient method for the carbonylative activation of benzotriazoles to benzoxazinones has been developed. By using a silver and palladium bimetallic catalyst system, a broad range of benzotriazoles were transformed into the corresponding benzoxazinones in moderate to good yields with excellent functional group tolerance. Notably, this procedure proceeds under neutral conditions.