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Two-dimensional MXenes have shown great promise for many different applications, but in order to fully utilize their potential, control of their termination groups is essential. Here we demonstrate hydrolyzation with a continuous gas flow as a method to remove F-terminations from multilayered V 2 C T x particles, in order to prepare nearly F-free and partly bare vanadium carbide MXene. Density functional theory calculations demonstrate that the substitution of F-terminations is thermodynamically feasible and presents partly nonterminated V 2 CO as the dominating hydrolyzation product. Hydrolyzation at elevated temperatures reduced the F content but only subtly changed the O content, as inferred from spectroscopic data. The ideal hydrolyzation temperature was found to be 300 °C, as a degradation of the V 2 C T x phase and a transition to vanadium oxycarbides and V 2 O 3 were observed at higher temperature. When tested as electrodes in Li-ion batteries, the hydrolyzed MXene demonstrated a reduced polarization compared with the pristine MXene, but no change in intercalation voltage was observed. Annealing in dry Ar did not result in the same F reduction, and the importance of water vapor was concluded, demonstrating hydrolyzation as a new and efficient method to control the surface terminations of multilayered V 2 C T x post etching. These results also provide new insights on the thermal stability of V 2 C T x MXene in hydrated atmospheres., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

To handle energetic materials safely, it is important to have knowledge about their sensitivity. Density functional theory (DFT) has proven a valuable tool in the study of energetic materials, and in the current work, DFT is employed to study the thermal unimolecular decomposition of 2,4,6-trinitrophenol (picric acid, PA), 3-methyl-2,4,6-trinitrophenol (methyl picric acid, mPA), and 3,5-dimethyl-2,4,6-trinitrophenol (dimethyl picric acid, dmPA). These compounds have similar molecular structures, but according to the literature, mPA is far less sensitive to impact than the other two compounds. Three pathways believed important for the initiation reactions are investigated at 0 and 298.15 K. We compare the computed energetics of the reaction pathways with the objective of rationalizing the unexpected sensitivity behavior. Our results reveal a few if any significant differences in the energetics of the three molecules, and thus do not reflect the sensitivity deviations observed in experiments. These findings point toward the potential importance of crystal structure, crystal morphology, bimolecular reactions, or combinations thereof on the impact sensitivity of nitroaromatics.

The realization of sustainable and cheap Mg-S batteries depends on significant improvements in cycling stability. Building on the immense research on cathode optimization from Li-S batteries, for the first time a beneficial role of MXenes for Mg-S batteries is reported. Through a facile, low-temperature vacuum-filtration technique, several novel current collector- and binder-free cathode films were developed, with either dipenthamethylene thiuram tetrasulfide (PMTT) or S 8 nanoparticles as the source of redox-active sulfur. The importance of combining MXene with a high surface area co-host material, such as carbon nanotubes, was demonstrated. A positive effect of MXenes on the average voltage and reduced self-discharge was also discovered. Ascribed to the rich polar surface chemistry of Ti 3 C 2 T x MXene, an almost doubling of the discharge capacity (530 vs. 290 mA h g -1 ) was achieved by using MXene as a polysulfide-confining interlayer, obtaining a capacity retention of 83 % after 25 cycles., (© 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

The present challenge with all-oxide thermoelectric modules is their poor durability at high temperatures caused by the instability of the metal-oxide interfaces at the hot side. This work explains a new module concept based on a hybrid p-n junction, fabricated in one step by spark plasma co-sintering of Ca 3 Co 4- x O 9+δ (CCO, p-type) and CaMnO 3-δ /CaMn 2 O 4 (CMO, n-type). Different module (unicouple) designs were studied to obtain a thorough understanding of the role of the in situ formed hybrid p-n junction of Ca 3 CoMnO 6 (CCMO, p-type) and Co-oxide rich phases (p-type) at the p-n junction (>700 °C) in the module performance. A time-enhanced performance of the modules attributed to this p-n junction formation was observed due to the unique electrical properties of the hybrid p-n junction being sufficiently conductive at high temperatures (>700 °C) and nonconductive at moderate and low temperatures. The alteration of module design resulted in a variation of the power density from 12.4 (3.1) to 28.9 mW/cm 2 (7.2 mW) at Δ T ∼ 650 °C after 2 days of isothermal hold (900 °C hot side). This new concept provides a facile method for the fabrication of easily processable, cheap, and high-performance high-temperature modules., Competing Interests: The authors declare no competing financial interest., (© 2020 American Chemical Society.)

An all-oxide thermoelectric generator for high-temperature operation depends on a low electrical resistance of the direct p-n junction. Ca 3 Co 4- x O 9+ δ and CaMnO 3- δ exhibit p-type and n-type electronic conductivity, respectively, and the interface between these compounds is the material system investigated here. The effect of heat treatment (at 900 °C for 10 h in air) on the phase and element distribution within this p-n junction was characterized using advanced transmission electron microscopy combined with X-ray diffraction. The heat treatment resulted in counter diffusion of Ca, Mn and Co cations across the junction, and subsequent formation of a Ca 3 Co 1+ y Mn 1- y O 6 interlayer, in addition to precipitation of Co-oxide, and accompanying diffusion and redistribution of Ca across the junction. The Co/Mn ratio in Ca 3 Co 1+ y Mn 1- y O 6 varies and is close to 1 ( y = 0) at the Ca 3 Co 1+ y Mn 1- y O 6 -CaMnO 3- δ boundary. The existence of a wide homogeneity range of 0 ≤ y ≤ 1 for Ca 3 Co 1+ y Mn 1- y O 6 is corroborated with density functional theory (DFT) calculations showing a small negative mixing energy in the whole range., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Calcium manganite-based perovskite-type oxides hold promise for application in chemical looping combustion processes and oxygen transport membranes. In this study, we have investigated the structure, electrical conductivity and oxygen transport properties of perovskite-type oxides CaMn1-x-yTixFeyO3-δ. Distinct from previous work, data of high-temperature X-ray diffraction (HT-XRD) in the temperature range 600-1000 °C (with intervals of 25 °C) demonstrates that CaMnO3-δ (CM) transforms from orthorhombic to a mixture of orthorhombic and tetragonal phases between 875 °C and 900 °C. Rietveld refinements show the formation of a pure tetragonal phase at 975 °C and of a pure cubic phase at 1000 °C. Partial substitution of manganese by iron and/or titanium to yield CaMn0.875Ti0.125O3-δ (CMT), CaMn0.85Fe0.15O3-δ (CMF) or CaMn0.725Ti0.125Fe0.15O3-δ (CMTF) leads to different phase behaviours. While CMT remains orthorhombic up to the highest temperature covered by the HT-XRD experiments, CMF and CMTF undergo an orthorhombic → tetragonal → cubic sequence of phase transitions. Electrical conductivity relaxation measurements are conducted to determine the chemical diffusion coefficient (Dchem) and the surface exchange coefficient (kchem) of the materials. The results demonstrate that oxygen transport is hindered in the tetragonal phase, when occurring, which is attributed to a possible ordering of oxygen vacancies. The small polaron electrical conductivity of CM in the cited temperature range is lowered upon partial manganese substitution, by about 10% for CMF and up to half an order of magnitude for CMT and CMTF.

High-temperature instability of the Ca₃Co 4- y O 9+ δ and CaMnO 3- δ direct p-n junction causing the formation of Ca₃Co 2- x Mn x O₆ has motivated the investigation of the thermoelectric performance of this intermediate phase. Here, the thermoelectric properties comprising Seebeck coefficient, electrical conductivity, and thermal conductivity of Ca₃Co 2- x Mn x O₆ with x = 0.05, 0.2, 0.5, 0.75, and 1 are reported. Powders of the materials were synthesized by the solid-state method, followed by conventional sintering. The material Ca₃CoMnO₆ ( x = 1) demonstrated a large positive Seebeck coefficient of 668 μV/K at 900 °C, but very low electrical conductivity. Materials with compositions with x < 1 had lower Seebeck coefficients and higher electrical conductivity, consistent with small polaron hopping with an activation energy for mobility of 44 ± 6 kJ/mol and where both the concentration and mobility of hole charge carriers were proportional to 1- x . The conductivity reached about 11 S·cm -1 at 900 °C for x = 0.05. The material Ca₃Co 1.8 Mn 0.2 O₆ ( x = 0.2) yielded a maximum zT of 0.021 at 900 °C. While this value in itself is not high, the thermodynamic stability and self-assembly of Ca₃Co 2- x Mn x O₆ layers between Ca₃Co 4- y O 9+ δ and CaMnO 3- δ open for new geometries and designs of oxide-based thermoelectric generators.

All-oxide thermoelectric modules for energy harvesting are attractive because of high-temperature stability, low cost, and the potential to use nonscarce and nontoxic elements. Thermoelectric modules are mostly fabricated in the conventional π-design, associated with the challenge of unstable metallic interconnects at high temperature. Here, we report on a novel approach for fabrication of a thermoelectric module with an in situ formed p-p-n junction made of state-of-the-art oxides Ca 3 Co 4- x O 9+δ (p-type) and CaMnO 3 -CaMn 2 O 4 composite (n-type). The module was fabricated by spark plasma co-sintering of p- and n-type powders partly separated by insulating LaAlO 3 . Where the n- and p-type materials originally were in contact, a layer of p-type Ca 3 CoMnO 6 was formed in situ. The hence formed p-p-n junction exhibited Ohmic behavior and a transverse thermoelectric effect, boosting the open-circuit voltage of the module. The performance of the module was characterized at 700-900 °C, with the highest power output of 5.7 mW (around 23 mW/cm 2 ) at 900 °C and a temperature difference of 160 K. The thermoelectric properties of the p- and n-type materials were measured in the temperature range 100-900 °C, where the highest zT of 0.39 and 0.05 were obtained at 700 and 800 °C, respectively, for Ca 3 Co 4- x O 9+δ and the CaMnO 3 -CaMn 2 O 4 composite., Competing Interests: The authors declare no competing financial interest.

Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the western nucleus of the merging galaxy pair Arp 299 that radiated >1.5 × 10 52 erg at infrared and radio wavelengths but was not luminous at optical or x-ray wavelengths. We interpret this as a TDE with much of its emission reradiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the difference between theoretical predictions and observed luminosities of TDEs. The radio observations resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH., (Copyright © 2018, American Association for the Advancement of Science.)

Diffusivity on the A- and B-site of polycrystalline perovskite CaMnO 3-δ with Ca deficiency and spinel CaMn 2 O 4 (marokite) as a secondary phase was studied using chemical tracers and secondary ion mass spectrometry (SIMS) complemented by electron probe microanalysis (EPMA). Thin films containing Sr and Co chemical tracers were deposited on the polished surface of the polycrystalline composite sample followed by annealing at 800-1200 °C for 96 h. Diffusion profiles for each tracer were determined with SIMS, followed by calculation of diffusion coefficients by fitting to appropriate models. The Sr tracer showed mainly lattice diffusion, with an activation energy of 210 ± 30 kJ mol -1 , whereas the Co tracer showed a combination of lattice and enhanced grain-boundary diffusion, with activation energies of 270 ± 30 kJ mol -1 and 380 ± 40 kJ mol -1 , respectively. The diffusivities may be used to predict interdiffusion and lifetime of junctions between n-type CaMnO 3-δ or CaMnO 3-δ /CaMn 2 O 4 composites and metallization interlayers or p-type leg materials in oxide thermoelectrics. In particular, the relatively high effective diffusivity of Co in polycrystalline CaMnO 3-δ may play a role in the reported fast formation of the secondary phase (Ca 3 Co 2-y Mn y O 6 ) between p-type Ca 3 Co 3.92 O 9+δ and n-type CaMnO 3-δ in a direct p-n thermoelectric junction.

Internationally adopted postinstitutionalized (PI) children are at risk for lower levels of emotion understanding. This study examined how postadoption parenting influences emotion understanding and whether lower levels of emotion understanding are associated with behavior problems. Emotion understanding and parent mental state language were assessed in 3-year-old internationally adopted PI children (N = 25), and comparison groups of children internationally adopted from foster care (N = 25) and nonadopted (NA) children (N = 36). At 5.5-year follow-up, PI children had lower levels of emotion understanding than NA children, a group difference not explained by language. In the total sample, parent mental state language at age 3 years predicted 5.5-year emotion understanding after controlling for child language ability. The association of parent mental state language and 5.5-year emotion understanding was moderated by adoption status, such that parent mental state language predicted 5.5-year emotion understanding for the internationally adopted children, but not for the NA children. While postadoption experience does not erase negative effects of early deprivation on emotion understanding, results suggest that parents can promote emotion understanding development through mental state talk. At 5.5 years, PI children had more internalizing and externalizing problems than NA children, and these behavioral problems related to lower levels of emotion understanding.

Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) (BSCF) with the cubic perovskite structure is known to be metastable at low temperature under an oxidizing atmosphere. Here, the thermal and chemical expansion of BSCF were studied by in situ high temperature powder X-ray diffraction and thermo-gravimetrical analysis (TGA) in partial pressure of oxygen ranging from an inert atmosphere (∼10(-4) bar) to 10 bar O(2). The BSCF powder, heat treated at 1000 °C and quenched to ambient temperature prior to the analysis, was shown to oxidize under an oxidizing atmosphere before thermal reduction took place. With decreasing partial pressure of oxygen the initial oxidation was suppressed and only reduction of Co/Fe and loss of oxygen were observed under an inert atmosphere. The thermal expansion of BSCF under different atmospheres was determined from the thermal evolution of the cubic unit cell parameter, demonstrating that the thermal expansion of BSCF depends on the atmosphere. Chemical expansion of BSCF was also estimated based on the diffraction data and thermo-gravimetrical analysis. A hexagonal perovskite phase, coexisting with the cubic BSCF polymorph, was observed to be formed above 600 °C during heating. The phase separation leading to the formation of the hexagonal polymorph was driven by oxidation, and the unit cell of the cubic BSCF was shown to decrease with increasing amounts of the hexagonal phase. The hexagonal phase disappeared upon further heating, accompanied with an expansion of the unit cell of the cubic BSCF.