PNb 9 O 25 , a Wadsley-Roth compound whose structure is obtained by appropriate crystallographic shear of the ReO 3 structure, is a high-power electrode material that can reach 85 % of the equilibrium capacity in 30 minutes and 67% in 6 minutes. Here we show that multielectron redox, as observed through X-ray absorption spectroscopy and X-ray photoelectron spectroscopy, and an insulator-to-metal transition upon lithium insertion, as suggested by a number of complementary techniques, contribute to the impressive performance. Chemically tuning the tetrahedral site between phosphorus and vanadium leads to significant changes in the electrochemistry and kinetics of lithium insertion in the structure, pointing to larger implications for the use of crystallographic shear phases as fast-charging electrode materials.

Transition metal perovskite chalcogenides, a class of materials with rich tunability in functionalities, are gaining increased attention as candidate materials for renewable energy applications. Perovskite oxides are considered excellent n-type thermoelectric materials.Compared to oxide counterparts, we expect the chalcogenides to possess more favorable thermoelectric properties such as lower lattice thermal conductivity and smaller band gap, making them promising material candidates for high temperature thermoelectrics. Thus, it is necessary to study the thermal properties of these materials in detail, especially thermal stability, to evaluate their potential. In this work, we report the synthesis and thermal stability study of five compounds, a-SrZrS 3 , b-SrZrS 3 , BaZrS 3 , Ba 2 ZrS 4 , and Ba 3 Zr 2 S 7 . These materials cover several structural types including distorted perovskite, needle-like, and Ruddlesden-Popper phases.Differential scanning calorimeter and thermo-gravimetric analysis measurements were performed up to 1200°C in air. Structural and chemical characterizations such as X-ray diffraction, Raman spectroscopy, and energy dispersive analytical X-ray spectroscopy were performed on all the samples before and after the heat treatment to understand the oxidation process. Our studies show that perovskite chalcogenides possess excellent thermal stability in air at least up to 600°C.

Crystalline solids exhibiting glass-like thermal conductivity have attracted substantial attention both for fundamental interest and applications such as thermoelectrics. In most crystals, the competition of phonon scattering by anharmonic interactions and crystalline imperfections leads to a non-monotonic trend of thermal conductivity with temperature. Defect-free crystals that exhibit the glassy trend of low thermal conductivity with a monotonic increase with temperature are desirable because they are intrinsically thermally insulating while retaining useful properties of perfect crystals. However, this behavior is rare, and its microscopic origin remains unclear. Here, we report the observation of ultralow and glass-like thermal conductivity in a hexagonal perovskite chalcogenide single crystal, BaTiS3, despite its highly symmetric and simple primitive cell. Elastic and inelastic scattering measurements reveal the quantum mechanical origin of this unusual trend. A two-level atomic tunneling system exists in a shallow double-well potential of the Ti atom and is of sufficiently high frequency to scatter heat-carrying phonons up to room temperature. While atomic tunneling has been invoked to explain the low-temperature thermal conductivity of solids for decades, our study establishes the presence of sub-THz frequency tunneling systems even in high-quality, electrically insulating single crystals, leading to anomalous transport properties well above cryogenic temperatures.

The effects of shear planes in perovskitic materials have been studied in order to identify their role in the electrochemical behavior and structural evolution of Li+ intercalation hosts.

A class of wide bandgap host materials is introduced as an alternative to carbazole-based hosts to enhance the efficiency and transport properties of organic light emitting diodes (OLEDs).

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Nitrous oxide (N 2 O), also known as laughing gas, is arguably one of the most detrimental greenhouse gases while concurrently being overlooked by the public. Specifically, N 2 O is ∼300 times more damaging than its better-known counterpart carbon dioxide (CO 2 ) and has a longer-lived lifetime in the atmosphere than CO 2 . There exist both natural and anthropogenic sources of N 2 O, and thus, for a better understanding of sources, capture, and decomposition, it is pivotal to identify N 2 O within the nitrogen biosphere. This review covers the past and current low-cost N 2 O gas-sensing technologies, focusing specifically on low-cost metal oxide semiconductors (MOSs), chemiresistive and electrochemical sensors that can provide spatial and temporal monitoring of N 2 O emissions from various sources. Additionally, compositional modifications to MOsS using metal− organic frameworks (MOFs) are discussed, potentially facilitating new awareness and efforts for increased sensing performance and functionality in N 2 O detection.

While high-performance piezoelectric polymeric nanofibers such as polyvinylidene fluoride and its derivatives have been extensively studied to various applications, limited works examined other functional piezoelectric organic polymers with different chemical functionalities. In this work, size- and conformation-dependent piezoelectric properties of polyacrylonitrile (PAN) nanofibers were systematically investigated. PAN nanofibers with diameters ranging from 40 to 600 nm were systematically synthesized by adjusting electrospinning solution conditions where their conformation was further tuned through post-thermal treatment. Through in situ poling and stretching of polymer chains, the electrospinning process allowed the alignment of polar functional groups along the nanofibers to form a greater fraction of the electroactive phase (i.e., zigzag) over 31 helical (nonelectroactive) conformation. Smaller fiber further increased the electroactive content by the dimensional confinement effect. Fourier-transform infrared spectroscopy analysis and X-ray diffraction analysis confirmed the enhancement of zigzag conformation over 31 helical by reducing the fiber diameter and postannealing. A piezoelectric charge constant of 39.0 pm/V was achieved via reducing the PAN nanofiber diameter down to 40 nm, followed by post-thermal treatment at 95 °C, which paved a way to develop a flexible high-performance nanogenerator with diverse chemical functionality.