Dielectric, pyroelectric, and ferroelectric studies in (1 - x)AgNbO3-xFeNbO4 lead-free ceramics.

In the present study, the effect of heterovalent Fe3+ ions on the dielectric, pyroelectric, and ferroelectric properties of the (1 - x)AgNbO3-xFeNbO4 (x = 0.005, 0.01, 0.025, 0.05, and 0.1) system was investigated. The substitution of smaller ionic radius Fe3+ in B-sites and the formation of FeNbO4 as a secondary phase contributed to improved dielectric performance, especially the pyroelectric effect, of (1 - x)AgNbO3-xFeNbO4 ceramics by generating electron-rich ceramics. The (1 - x)AgNbO3-xFeNbO4 ceramics were prepared by conventional solid-state sintering. Pure AgNbO3 had a perovskite crystal structure with an orthorhombic crystal system, but the FeNbO4 in (1 - x)AgNbO3-xFeNbO4 ceramics was formed as a secondary phase with a monoclinic structure. In addition, the XRD and Raman spectroscopy data showed that some Fe3+ was substituted into B-sites of AgNbO3. The introduction of FeNbO4 effectively reduced the average grain size from 1.85 ± 0.09 µm to 1.22 ± 0.03 µm for pure AgNbO3 and 0.9AgNbO3-0.1FeNbO4, respectively. In addition, the relative density of the (1 - x)AgNbO3-xFeNbO4 ceramics decreased from 97.96% ± 0.01 for x = 0 to 96.75% ± 0.03 for x = 0.1. The real part of the permittivity ε', at room temperature, increased from 186.6 for x = 0 to a value of 738.7 for x = 0.1. Additionally, the maximum pyroelectric coefficient increased fivefold, reaching values of 2270 nC cm-2 K-1 for x = 0.1. Furthermore, a harvested pyroelectric energy density (W) of 1140 µJ cm-3 for x = 0.025 was achieved, which is appreciably higher than the 840 µJ cm-3 value for x = 0.

Climate-induced hydrological fluctuations shape Arctic Alaskan peatland plant communities.

Rapidly increasing temperatures in high-latitude regions are causing major changes in wetland ecosystems. To assess the impact of concomitant hydroclimatic fluctuations, mineral deposition, and autogenous succession on the rate and direction of changing arctic plant communities in Arctic Alaska, we conducted detailed palaeoecological analyses using plant macrofossil, pollen, testate amoebae, elemental analyses, and radiocarbon and lead (210Pb) dating on two replicate monoliths from a peatland that developed in a river valley on the northern foothills of the Books Range. We observed an expansion of Sphagnum populations and vascular plants preferring dry habitats, such as Sphagnum warnstorfii, Sphagnum teres/squarrosum, Polytrichum strictum, Aulacomnium palustre and Salix sp., in recent decades between 2000 and 2015 CE, triggered by an increase in temperature and deepening water tables. Deepening peatland water tables became accentuated over the last two decades, when it reached its lowest point in the last 700 years. Conversely, a higher water-table between ca. 1500 and 1950 CE led to a recession of Sphagnum communities and an expansion of sedges. The almost continuous supply of mineral matter during this time led to a dominance of minerotrophic plant communities, although with varying species composition throughout the study period. The replicate cores show similar patterns, but nuanced differences are also visible, depicting fine spatial scale differences particularly in peat-forming plant distribution and the different timings of their presence. In conclusion, our study provides valuable insights into the impact of hydroclimatic fluctuations on peatland vegetation in Arctic Alaska, highlighting their tendency to dry out in recent decades. It also highlights the importance of river valley peatlands in paleoenvironmental reconstructions.

Enhanced energy storage performance in reaction-sintered AgNbO3 antiferroelectric ceramics.

In this research, AgNbO3 ceramics were produced by two sintering methods: reaction sintering (RS) and conventional solid-state sintering (CSSS). The process was similar for both methods, except that in RS, Ag2O and Nb2O5 precursors were mixed, then formed into pellets, skipping the calcination step, and sintered at 1100 °C for 6 hours. Both prepared ceramics had the same perovskite crystal structure with an orthorhombic crystal system and Pbcm and Pmc21 space groups with similar lattice dynamic vibration modes at room temperature. The average grain size of the polycrystalline samples prepared by RS and CSSS was found to be ∼2.03 ± 0.77 and ∼1.85 ± 0.96 µm, respectively. The relative bulk densities of the ceramics produced by RS and CSSS were found to be ∼94.0 ± 1.8 and ∼96.5 ± 1.3%, respectively. Ceramics prepared by both methods showed antiferroelectric behavior, and reaction-sintered AgNbO3 ceramics exhibited lower energy loss density than CSSS samples. In addition, a recoverable energy storage density (Wrec) of 3.1 J cm-3 and higher energy storage efficiency (η) for RS samples were measured at 175 kV cm-1. Moreover, the η values of 74.2% and 57.7% were measured for samples sintered by RS and CSSS, respectively. This energy storage efficiency is the highest ever reported for pure AgNbO3 ceramics. Furthermore, reaction-sintered samples showed good temperature stability for Wrec and η in the 30-80 °C temperature range.

Recent climate change has driven divergent hydrological shifts in high-latitude peatlands.

High-latitude peatlands are changing rapidly in response to climate change, including permafrost thaw. Here, we reconstruct hydrological conditions since the seventeenth century using testate amoeba data from 103 high-latitude peat archives. We show that 54% of the peatlands have been drying and 32% have been wetting over this period, illustrating the complex ecohydrological dynamics of high latitude peatlands and their highly uncertain responses to a warming climate.

Pillar[5]arene-Based Polycationic Glyco[2]rotaxanes Designed as Pseudomonas aeruginosa Antibiofilm Agents.

Pseudomonas aeruginosa (P.A.) is a human pathogen belonging to the top priorities for the discovery of new therapeutic solutions. Its propensity to generate biofilms strongly complicates the treatments required to cure P.A. infections. Herein, we describe the synthesis of a series of novel rotaxanes composed of a central galactosylated pillar[5]arene, a tetrafucosylated dendron, and a tetraguanidinium subunit. Besides the high affinity of the final glycorotaxanes for the two P.A. lectins LecA and LecB, potent inhibition levels of biofilm growth were evidenced, showing that their three subunits work synergistically. An antibiofilm assay using a double ΔlecAΔlecB mutant compared to the wild type demonstrated that the antibiofilm activity of the best glycorotaxane is lectin-mediated. Such antibiofilm potency had rarely been reached in the literature. Importantly, none of the final rotaxanes was bactericidal, showing that their antibiofilm activity does not depend on bacteria killing, which is a rare feature for antibiofilm agents.

Dynamic Constitutional Frameworks as Antibacterial and Antibiofilm Agents.

Dynamic constitutional frameworks (DCFs) were synthesized and screened for biofilm inhibition or disruption. They are composed of a trialdehyde core reversibly linked to a diamine PEG connector and to a variety of neutral, anionic, or cationic heads, to generate a library of DCFs to generate multivalent dendritic architectures in the presence of Pseudomonas aeruginosa and Staphylococcus aureus. The best DCFs were always polycationic and the nature of the cationic heads significantly impact the antibiofilm activity. The best antibiofilm activity was observed for DCF3B, displaying a polyethyleneimine head. A simple inactive guanidinium functional head strongly inhibited biofilm growth when assayed as a multivalent DCF3C. Using a more advanced in vitro biofilm model of chronic wound infection, DCF3C was found significantly superior than all other DCFs. These results demonstrate the versatility and effectiveness of DCFs as low cost and efficient systems for antibiofilm disruption.

How Joannites' economy eradicated primeval forest and created anthroecosystems in medieval Central Europe.

During European states' development, various past societies utilized natural resources, but their impact was not uniformly spatially and temporally distributed. Considerable changes resulted in landscape fragmentation, especially during the Middle Ages. Changes in state advances that affected the local economy significantly drove trajectories of ecosystems' development. The legacy of major changes from pristine forest to farming is visible in natural archives as novel ecosystems. Here, we present a high-resolution densely dated multi-proxy study covering the last 1500 years from a peatland located in CE Europe. The economic activity of medieval societies was highly modified by new rulers-the Joannites (the Order of St. John of Jerusalem, Knights Hospitaller). We studied the record of these directorial changes noted in the peat profile. Our research revealed a rapid critical land-use transition in the late Middle Ages and its consequences on the peatland ecosystem. The shift from the virgin forest with regular local fires to agriculture correlates well with the raising of local economy and deforestations. Along with the emerging openness, the wetland switched from alkaline wet fen state to acidic, drier Sphagnum-dominated peatland. Our data show how closely the ecological state of wetlands relates to forest microclimate. We identified a significant impact of the Joannites who used the novel farming organization. Our results revealed the surprisingly fast rate of how feudal economy eliminated pristine nature from the studied area and created novel anthroecosystems.

Cationic dynamic covalent polymers for gene transfection.

Dynamic covalent polymers are materials formed by reversible covalent bonds and non-covalent interactions through an adaptive constitutional dynamic chemistry. The implementation of dynamic covalent polymers in gene delivery has recently emerged due to their responsive and adaptive features. Indeed, such an approach offers the alluring promise of discovering optimal delivery vectors self-fitted to their nucleic acid cargos and responsive to environmental changes (e.g. pH changes or the presence of a biomolecular target). This review will discuss more precisely the structural features of the molecular building blocks used so far, the architecture of the resulting dynamic covalent polymers from linear to 2D and 3D, and the covalent and supramolecular self-assembly processes at play in nucleic acid recognition and delivery, showcasing in particular the very few examples of adaptive self-assembly of dynamic covalent polymers templated by nucleic acids and responsive to the presence of biomolecular targets found in cell membranes that facilitate cell entry.

Microwave-Assisted Synthesis of an Alternant Poly(fluorene-oxadiazole). Synthesis, Properties, and White Light-Emitting Devices.

An alternant poly(dihexyl fluorene-co diphenyl oxadiazole) has been synthetized by microwave-assisted oxidative polymerization. The structure has been confirmed by 1H-NMR and FTIR spectroscopies. Gel permeation chromatography indicated high molecular weight and low polydispersity index. DFT calculations suggested a complete separation of HOMO and LUMO orbitals, which were located on fluorene and oxadiazole moiety, respectively. X-ray diffraction, polarized light microscopy, and atomic force microscopy indicated the polymer tendency to stack into a layered morphology with a more compact structure for the films prepared by spin coating. Furthermore, UV-vis and photoluminescence spectroscopies indicated the formation of H-aggregates which played a key role in photoluminescence quenching in solid state. Nevertheless, the good charge mobility gained due to the orbital overlapping in H-aggregates led to excellent electroluminescence, which enabled the development of white OLED devices with outstanding stability.

Piezoresistive Effect in the [Fe(Htrz)2(trz)](BF4) Spin Crossover Complex.

We report on the effect of hydrostatic pressure on the electrical conductivity and dielectric permittivity of the [Fe(Htrz)2(trz)](BF4) (Htrz = 1H-1,2,4,-triazole) spin crossover complex. Variable-temperature and -pressure broad-band impedance spectrometry revealed a piezoresistive effect of more than 1 order of magnitude for pressures as low as 500 bar, associated with a large pressure-induced hysteresis of 1700 bar. The origin of the piezoresistive effect has been attributed to the pressure-induced spin state switching in the complex, and the associated P,T phase diagram was determined.