Achieving Superior Thermoelectric Performance in Ge4Se3Te via Symmetry Manipulation with I–V–VI2 Alloying

Although orthorhombic GeSe is predicted to have an ultrahigh figure of merit, ZT ≈ 2.5, up to now, the highest experimental value is ≈0.2 due to the low carrier concentration (n_H ≈ 10¹⁸ cm⁻³). Improving symmetry is an effective approach for enhancing the ZT of GeSe-based materials. With Te-alloying, Ge₄Se₃Te displays the two-dimensional hexagonal structure and high n_H ≈ 1.23 × 10²¹ cm⁻³. Interestingly, Ge₄Se₃Te transformed from the hexagonal into the rhombohedral phase with only ≈2% I–V–VI₂-alloying (I = Li, Na, K, Cu, Ag; V = Sb, Bi; VI = Se, Te). According to the calculated results of Ge_0.82Ag_0.09Bi_0.09Se_0.614Te_0.386 single-crystal grown via AgBiTe₂-alloying, it exhibits a higher valley degeneracy than the hexagonal Ge₄Se₃Te. For instance, AgBiTe₂-alloying induces a strong band convergence and band inversion effect, resulting in a significantly enhanced Seebeck coefficient and power factor with a similar n_H from 17 µV K⁻¹ and 0.63 µW cm⁻¹ K⁻² for pristine Ge₄Se₃Te to 124 µV K⁻¹ and 5.97 µW cm⁻¹ K⁻² for 12%AgBiTe₂-alloyed sample, respectively. Moreover, the sharply reduced phonon velocity, nano-domain wall structure, and strong anharmonicity lead to low lattice thermal conductivity. As a result, a record-high average ZT ≈0.95 over 323–773 K with an excellent ZT ≈ 1.30 is achieved at 723 K.     

Oxygen Defects Engineering of VO2·xH2O Nanosheets via In Situ Polypyrrole Polymerization for Efficient Aqueous Zinc Ion Storage

What has been a crucial demand is that designing mighty cathode materials for aqueous zinc−ion batteries (AZIBs), which are vigorous alternative devices for large−scale energy storage by means of their high safety and low cost. Herein, a facile strategy is designed that combines oxygen defect engineering with polymer coating in a synergistic action. As an example, the oxygen−deficient hydrate vanadium dioxide with polypyrrole coating (O_d−HVO@PPy) is synthesized via a one-step hydrothermal method in which introducing oxygen vacancy in HVO is simultaneously realized during the in situ polymerization. Such a desirable material adjusts the surface adsorption and internal diffusion of Zn²⁺ demonstrated by electrochemical characterization and theoretical calculation results. Moreover, it also utilizes conductive polymer coating to improve electrical conductivity and suppress cathode dissolution. Therefore, the O_d−HVO@PPy electrode delivers a preferable reversible capacity (337 mAh g⁻¹ at 0.2 A g⁻¹) with an impressive energy density of 228 Wh kg⁻¹ and stable long cycle life. This enlightened design opens up a new modus operandi toward superior cathode materials for advanced AZIBs.     

Growth behavior and improved water–vapor-permeation-barrier properties of 10-nm-thick single Al2O3 layer grown via cyclic chemical vapor deposition on organic light-emitting diodes

We have investigated the growth behavior and water vapor permeation barrier properties of cyclic chemical vapor deposition (C-CVD)-grown 10-nm-thick single layer of Al₂O₃. Al₂O₃ layers grown by C-CVD showed a high density of 3.298 g/cm³ and were amorphous without grain boundaries. A deposition rate of 0.46 nm/cycle was obtained. The C-CVD system was self-limiting, as in the case of atomic layer deposition, which enables precise control of the thickness of the Al₂O₃ layer. A water vapor transmission rate of 1.51 × 10⁻⁵ (g/m²)/day was obtained from a Ca degradation test performed at 85 °C and 85% relative humidity. Moreover, the performance of organic light-emitting diodes, passivated by a C-CVD-grown 10-nm-thick Al₂O₃ single layer, was not affected after 24,000 h of turn-on time; this is strong evidence that C-CVD-grown Al₂O₃ layers effectively prevent water vapor from diffusing into the active organic layer.     

Preparation and Dielectric Characteristics of Semitransparent CoFe2O4–P(VDF-TrFE) Nanocomposite Films

Polymer–ceramic nanocomposites play an important role in embedded capacitors. However, polymer–ceramic dielectrics are limited for commercial applications due to their low transmittance, poor adhesion, and poor thermal stress reliability at high filler loadings. Thus, materials design and processing is critical to prepare films with improved dielectric properties and low filler loading. In this work, we use a spin coating-assisted method to fabricate poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]–CoFe₂O₄ (CFO) nanocomposite films. Magnetic CFO nanoparticles in the size range of 10 nm to 40 nm were successfully synthesized using a hydrothermal process. The dispersion of the nanoparticles, the dielectric properties, and the transmittance of the nanocomposite films were studied. The dielectric constant of the nanocomposite films increased by about 45% over the frequency range of 100 Hz to 1 MHz, compared with that of pristine P(VDF-TrFE) film. Optical measurements indicated that the transmittance of the films remains above 60% in the visible range, indicating a relatively low content of CFO in the polymer matrix. Our experimental results suggest that spin coating-assisted dispersion may be a promising route to fabricate dielectric polymer–ceramic nanocomposite films of controllable thickness.     

Design and Directional Growth of (Mg1−xZnx)(Al1−yCry)2O4 Single-Crystal Fibers for High-Sensitivity and High-Temperature Sensing Based on Lattice Doping Engineering and Acoustic Anisotropy

High-performance temperature sensors for the harsh environment are vital components for meeting the increasing demands for the development of existing and emerging technologies. In this study, specifically oriented (Mg_1−xZn_x)(Al_1−yCr_y)₂O₄ single-crystal fibers (SCF) are grown by the laser-heated pedestal growth technique and used as acoustic waveguides for ultrasonic temperature sensors (UTS) for the first time. The anisotropic sensor performance of the MgAl₂O₄ SCF-UTS are investigated under a longitudinal wave and transverse wave conditions, and the [110]-oriented MgAl₂O₄ SCF-UTS is found to have the highest sensitivity and resolution among all the MgAl₂O₄ SCF-UTS. On this basis, a unit sensitivity of 40.38–67.50 ns °C⁻¹ m⁻¹ and a resolution of 1.24–0.74 °C are achieved for the [110]-oriented (Mg_0.9Zn_0.1)(Al_0.995Cr_0.005)₂O₄ SCF-UTS in the range of 20–1200 °C, both of which represent the best sensor performance achieved by a SCF-UTS to date. The positive temperature-dependent sensor performance, accompanied by a high working temperature (≈2000 °C) and outstanding anti-oxidation, indicates that the [110]-oriented (Mg_0.9Zn_0.1)(Al_0.995Cr_0.005)₂O₄ SCF-UTS is a promising candidate for ultra-high temperature sensors. This study demonstrates a feasible strategy for the rational design of high-performance temperature sensors through a combination of crystal design, acoustic anisotropy, and lattice doping engineering.     

Ferroelectric,Ferromagnetic, and Magnetoelectric Properties of Multiferroic Ni0.5Zn0.5Fe2O4–BaTiO3 Composite Ceramics

Lead-free multiferroic composite ceramics xNi_0.5Zn_0.5Fe₂O₄–(1 ? x)BaTiO₃ (x = 0.2, 0.5, 0.8) with a 0–3-type connection structure have been prepared by a traditional ceramic process. The cubic spinel Ni_0.5Zn_0.5Fe₂O₄ phase and the tetragonal perovskite BaTiO₃ phase were confirmed by x-ray diffraction. The effect of Ni_0.5Zn_0.5Fe₂O₄ ferrite content on ferroelectric and ferromagnetic behavior, and the magnetoelectric coupling effect of the composite ceramics is discussed. With increasing Ni_0.5Zn_0.5Fe₂O₄ ferrite content, the saturation magnetization of the composite ceramic increased and the saturation polarization decreased. The magnetoelectric coupling response voltage was observed to decrease rapidly for samples with x = 0.2, then 0.5, then 0.8. The highest magnetoelectric coupling response voltage, measured for 0.2Ni_0.5Zn_0.5Fe₂O₄–0.8BaTiO₃, was 150 μV, which corresponds to a maximum magnetoelectric coupling voltage coefficient of 109 μV/cm Oe. When x = 0.5, the maximum magnetoelectric response voltage is only 8 μV, and when x = 0.8, no magnetoelectric response voltage is detected because of very large leakage current of the 0.8Ni_0.5Zn_0.5Fe₂O₄–0.2BaTiO₃ composite ceramic.