Giant Deformation Induced Staggered-Layer Structure Promoting the Thermoelectric and Mechanical Performance in n-Type Bi2(Te, Se)3.

Bismuth telluride has long been recognized as the most promising near-room temperature thermoelectric material for commercial application; however, the thermoelectric performance for n-type Bi2(Te, Se)3-based alloys is far lagging behind that of its p-type counterpart. In this work, a giant hot deformation (GD) process is implemented in an optimized Bi2Te2.694Se0.3I0.006+3 wt%K2Bi8Se13 precursor and generates a unique staggered-layer structure. The staggered-layered structure, which is only observed in severely deformed crystals, exhibits a preferential scattering on heat-carrying phonons rather than charge-carrying electrons, thus resulting in an ultralow lattice thermal conductivity while retaining high-weight carrier mobility. Moreover, the staggered-layer structure is located adjacent to the van der Waals gap in Bi2(Te, Se)3 lattice and is able to strengthen the interaction between anion layers across the gap, leading to obviously improved compressive strength and Vickers hardness. Consequently, a high peak figure of merit ZT of ≈ 1.3 at 423 K, and an average ZT of ≈ 1.2 at 300-473 K can be achieved in GD sample. This study demonstrates that the GD process can successfully decouple the electrical and thermal transports with simultaneously enhanced mechanic performance.

Giant dielectric response and relaxation behavior of Bi3+/W6+ co-doped TiO2 ceramics.

With the rapid development of electronic information technology, dielectric ceramics are widely used in the field of passive devices such as multi-layer ceramic capacitors. In this paper, (Bi2/3W1/3)xTi1-xO2 (BWTOx) ceramics with superior dielectric properties have been prepared by using a traditional solid-state method. Remarkably, at a (Bi2/3W1/3)4+ doping level of 0.01, a (Bi2/3W1/3)0.01Ti0.99O2 ceramic achieved a giant dielectric permittivity of ∼1.5 × 104 and a low loss tangent of ∼0.07 at 1 kHz, as well as a good temperature independence, which could satisfy the operating temperature standards for X9R capacitors. The abnormal dielectric relaxation in the low temperature region can be explained by the interface polarization. Data based on the complex impedance spectroscopy and X-ray photoemission spectroscopy results indicate that the colossal permittivity of BWTOx ceramics is mainly ascribed to the internal barrier layer capacitance effect. The findings of this work could provide valuable insights for achieving large dielectric constants and good temperature stability simultaneously in BWTOx and other related electronic ceramic materials.

Long-term stable and efficient degradation of ornidazole with minimized by-product formation by a biological sulfidogenic process based on elemental sulfur.

Conventional biological treatment processes cannot efficiently and completely degrade nitroimidazole antibiotics, due to the formation of highly antibacterial and carcinogenic nitroreduction by-products. This study investigated the removal of a typical nitroimidazole antibiotic (ornidazole) during wastewater treatment by a biological sulfidogenic process based on elemental sulfur (S0-BSP). Efficient and stable ornidazole degradation and organic carbon mineralization were simultaneously achieved by the S0-BSP in a 798-day bench-scale trial. Over 99.8 % of ornidazole (200‒500 µg/L) was removed with the removal rates of up to 0.59 g/(m3·d). Meanwhile, the efficiencies of organic carbon mineralization and sulfide production were hardly impacted by the dosed ornidazole, and their rates were maintained at 0.15 kg C/(m3·d) and 0.49 kg S/(m3·d), respectively. The genera associated with ornidazole degradation were identified (e.g., Sedimentibacter, Trichococcus, and Longilinea), and their abundances increased significantly. Microbial degradation of ornidazole proceeded by several functional genes, such as dehalogenases, cysteine synthase, and dioxygenases, mainly through dechlorination, denitration, N-heterocyclic ring cleavage, and oxidation. More importantly, the nucleophilic substitution of nitro group mediated by in-situ formed reducing sulfur species (e.g., sulfide, polysulfides, and cysteine hydropolysulfides), instead of nitroreduction, enhanced the complete ornidazole degradation and minimized the formation of carcinogenic and antibacterial nitroreduction by-products. The findings suggest that S0-BSP can be a promising approach to treat wastewater containing multiple contaminants, such as emerging organic pollutants, organic carbon, nitrate, and heavy metals.

The origin of dielectric relaxation behavior in TiO2 based ceramics co-doped with Zn2+, W6+ ions under a N2/O2 sintering atmosphere.

Dense (Zn0.5W0.5)xTi1-xO2 (ZWTOx) ceramics were fabricated using a conventional solid state reaction method with sintering under a nitrogen atmosphere (ZWTOx-N2) and an oxygen atmosphere (ZWTOx-O2), respectively. Colossal permittivity (ε > 104) and low loss (tan δ < 0.1) were simultaneously achieved in ZWTOx-N2 ceramics, and two types of dielectric relaxation behaviors observed were interpreted to be due to interface polarization and disassociation between oxygen vacancies and trivalent titanium ions, respectively. The impedance plots suggested that the ZWTOx-N2 ceramics are electrical heterostructures composed of semiconductor and insulator grain boundaries, which proved that the CP performance of ZWTOx-N2 ceramics almost originates from the internal barrier layer capacitance (IBLC) effect. In addition, a series of anomalous dielectric behaviors such as low permittivity and low frequency dispersion were observed for ZWTOx-O2 ceramics; polarization (P)-electric field (E) hysteresis loop curves were obtained for ZWTOx-O2 ceramics, and that impedance plots have shown that the ZWTOx-O2 ceramics display higher insulation resistivity. Density functional theory (DFT) calculations illustrated that the Zn2+-W6+ ion pairs are easy to form in ZWTOx-O2 ceramics, which causes destruction of the local lattice and thus leads to abnormal dielectric behavior. This work will provide a new strategy for defect engineering in TiO2 and other CP materials.

Superior Energy Storage Properties and Optical Transparency in K0.5 Na0.5 NbO3 -Based Dielectric Ceramics via Multiple Synergistic Strategies.

Eco-friendly transparent dielectric ceramics with superior energy storage properties are highly desirable in various transparent energy-storage electronic devices, ranging from advanced transparent pulse capacitors to electro-optical multifunctional devices. However, the collaborative improvement of energy storage properties and optical transparency in KNN-based ceramics still remains challenging. To address this issue, multiple synergistic strategies are proposed, such as refining the grain size, introducing polar nanoregions, and inducing a high-symmetry phase structure. Accordingly, outstanding energy storage density (Wtotal  ≈7.5 J cm-3 , Wrec  ≈5.3 J cm-3 ) and optical transmittance (≈76% at 1600 nm, ≈62% at 780 nm) are simultaneously realized in the 0.94(K0.5 Na0.5 )NbO3 -0.06Sr0.7 La0.2 ZrO3 ceramic, together with satisfactory charge-discharge performances (discharge energy density: ≈2.7 J cm-3 , power density: ≈243 MW cm-3 , discharge rate: ≈76 ns), surpassing previously reported KNN-based transparent ceramics. Piezoresponse force microscopy and transmission electron microscopy revealed that this excellent performance can be attributed to the nanoscale domain and submicron-scale grain size. The significant improvement in the optical transparency and energy storage properties of the materials resulted in the widening of the application prospects of the materials.

All Cubic-Phase δ-TAGS Thermoelectrics Over the Entire Mid-Temperature Range.

GeTe-based pseudo-binary (GeTe)x (AgSbTe2 )100- x (TAGS-x) is recognized as a promising p-type mid-temperature thermoelectric material with outstanding thermoelectric performance; nevertheless, its intrinsic structural transition and metastable microstructure (due to Ag/Sb/Ge localization) restrict the long-time application of TAGS-x in practical thermoelectric devices. In this work, a series of non-stoichiometric (GeTe)x (Ag1- δ Sb1+ δ Te2+ δ )100- x (x = 85∼50; δ = ≈0.20-0.23), referred to as δ-TAGS-x, with all cubic phase over the entire testing temperature range (300-773 K), is synthesized. Through optimization of crystal symmetry and microstructure, a state-of-the-art ZTmax of 1.86 at 673 K and average ZTavg of 1.43 at ≈323-773 K are realized in δ-TAGS-75 (δ = 0.21), which is the highest value among all reported cubic-phase GeTe-based thermoelectric systems so far. As compared with stoichiometric TAGS-x, the remarkable thermoelectric achieved in cubic δ-TAGS-x can be attributed to the alleviation of highly (electrical and thermal) resistive grain boundary Ag8 GeTe6 phase. Moreover, δ-TAGS-x exhibits much better mechanical properties than stoichiometric TAGS-x, together with the outstanding thermoelectric performance, leading to a robust single-leg thermoelectric module with ηmax of ≈10.2% and Pmax of ≈0.191 W. The finding in this work indicates the great application potential of non-stoichiometric δ-TAGS-x in the field of mid-temperature waste heat harvesting.

Metal-Free Halide Perovskite Single Crystals with Very Long Charge Lifetimes for Efficient X-ray Imaging.

Metal-free halide perovskites, as a specific category of the perovskite family, have recently emerged as novel semiconductors for organic ferroelectrics and promise the wide chemical diversity of the ABX3 perovskite structure with mechanical flexibility, light weight, and eco-friendly processing. However, after the initial discovery 17 years ago, there has been no experimental information about their charge transport properties and only one brief mention of their optoelectronic properties. Here, growth of large single crystals of metal-free halide perovskite DABCO-NH4 Br3 (DABCO = N-N'-diazabicyclo[2.2.2]octonium) is reported together with characterization of their instrinsic optical and electronic properties and demonstration, of metal-free halide perovskite optoelectronics. The results reveal that the crystals have an unusually large semigap of ≈16 eV and a specific band nature with the valence band maximum and the conduction band minimum mainly dominated by the halide and DABCO2+ , respectively. The unusually large semigap rationalizes extremely long lifetimes approaching the millisecond regime, leading to very high charge diffusion lengths (tens of µm). The crystals also exhibit high X-ray attenuation as well as being lightweight. All these properties translate to high-performance X-ray imaging with sensitivity up to 173 µC Gyair -1 cm-2 . This makes metal-free perovskites novel candidates for the next generation of optoelectronics.