No abstract

No abstract

A record high zT of 2.2 at 740 K is reported in Ge0.92Sb0.08Te single crystals, with an optimal hole carrier concentration ≈4 × 1020 cm−3 that simultaneously maximizes the power factor (PF) ≈56 µW cm−1 K−2 and minimizes the thermal conductivity ≈1.9 Wm−1 K−1. In addition to the presence of herringbone domains and stacking faults, the Ge0.92Sb0.08Te exhibits significant modification to phonon dispersion with an extra phonon excitation around ≈5–6 meV at Γ point of the Brillouin zone as confirmed through inelastic neutron scattering (INS) measurements. Density functional theory (DFT) confirmed this phonon excitation, and predicted another higher energy phonon excitation ≈12–13 meV at W point. These phonon excitations collectively increase the number of phonon decay channels leading to softening of phonon frequencies such that a three‐phonon process is dominant in Ge0.92Sb0.08Te, in contrast to a dominant four‐phonon process in pristine GeTe, highlighting the importance of phonon engineering approaches to improving thermoelectric (TE) performance.

No abstract

Recently, the anisotropic single crystalline SnSe has gained tremendous interest as a promising thermoelectric material. The elastic constants of such anisotropic crystals are notoriously difficult to measure yet play a crucial role in many thermodynamic properties. We report for the first time the nine independent elastic constants of its stiffness tensor as measured by resonant ultrasound spectroscopy. Our experimental values of the elastic constants are in good agreement with those reported by the density functional theory of SnSe, except for C 12 . The Voigt−Reuss− Hill method was used to determine the isotropic polycrystalline elastic moduli from the measured elastic constants of SnSe, which were found to be in agreement with theoretical values. Notably, the heat capacity of single crystalline SnSe deduced from our measured elastic moduli is in excellent agreement with the room temperature value of heat capacity determined from thermal transport measurements.

We examine the effect of nitrogen dopants in Few-layer graphene (FLG) cathodes on anion intercalation. Different nitrogen dopant configurations within the FLG were achieved by varying the synthesis parameters and their effects are compared. The dopant configurations of the samples were determined via X-ray photoelectron spectroscopy (XPS) and formation energies were calculated using density functional theory, allowing correlation between cell performance and dopant configuration. The reduced ion intercalation within the nitrogen doped FLG, and thus poor charge/discharge characteristics of nitrogen doped FLG cathodes, is attributed to the reduced mobility of the chloroaluminate ions in the presence of nitrogen dopants.The use of few-layer graphene (FLG) as a cathode in aluminum-ion batteries (AIBs) has recently attracted much interest, largely due to the 2015 report by Lin et al. [1] AIBs have the potential to *The Manuscript Click here to view linked References

Hexagonal boron nitride (h‐BN) and exfoliated nanosheets (BNNs) not only resemble their carbon counterparts graphite and graphene nanosheets in structural configurations and many excellent materials characteristics, especially the ultra‐high thermal conductivity, but also offer other unique properties such as being electrically insulating and extreme chemical stability and oxidation resistance even at elevated temperatures. In fact, BNNs as a special class of 2‐D nanomaterials have been widely pursued for technological applications that are beyond the reach of their carbon counterparts. Highlighted in this article are significant recent advances in the development of more effective and efficient exfoliation techniques for high‐quality BNNs, the understanding of their characteristic properties, and the use of BNNs in polymeric nanocomposites for thermally conductive yet electrically insulating materials and systems. Major challenges and opportunities for further advances in the relevant research field are also discussed.

Triboelectric nanogenerators (TENGs) convert mechanical energy, e.g., from human motions, into electrical power. The mechanical force brings two triboelectric materials with different electron affinities into contact, resulting in a voltage that can be used to power a device. Although progress has been made in identifying high‐performance triboelectric materials (e.g., polytetrafluoroethylene, MXenes, polyethylene terephthalate (PET), graphene‐impregnated polymers, and polyimide), the search for better triboelectric materials continues in order to harvest mechanical energy efficiently. Here, it is demonstrated that the output performance of a TENG can be enhanced by coating its triboelectric material surface with an important class of carbons, viz., zero‐dimensional C60 fullerene, which is known for its high electron affinity. Specifically, a C60 fullerene‐based TENG (F‐TENG) is fabricated and evaluated that supports a high open‐circuit voltage of ≈1.6 kV, short‐circuit current of ≈100 µA, instantaneous peak power density of ≈38 W m−2, and charging of a 1 µF capacitor to 180 V under 8 min. Because of the superior power output of the F‐TENG, a digital watch can be powered continuously in real‐time, a task that cannot be performed with a similar‐sized TENG comprising PET and polyimide. Notably, a novel methodology based on the analysis of the TENG output waveforms is presented for determining the triboelectric charge, which can then be used to rank the electrode material in the tribolelectric series.