Decoding the Atomic-Scale Structural Origin of Large Strain Performance in BNT-6BT Based Relaxor Ferroelectrics.

The relationship between matter properties and their atomic-scale structures is a challenging investigation. For relaxor ferroelectrics, correlating the relaxor mechanisms on the atomic scale to properties is still ambiguous. Here, the correlation between the atomic-scale structure and strain performance of 0.94 Bi0.5Na0.5TiO3-0.06BaTiO3 (94BNT-6BT) and 0.93 Bi0.5Na0.5TiO3-0.06BaTiO3-0.01BaZrO3 (93BNT-6BT-1BZ) is reported. The δTi-Bi/Na displacement vector map based on the annular dark field (ADF) scanning transmission electron microscopy (STEM) image demonstrates the coexistence of tetragonal (T) and rhombohedral (R) phases of the resulting ceramics, and BZ doping increases the proportion of the T phase. Furthermore, the enhanced annular bright field (eABF) STEM image demonstrates that BZ doped ceramics exhibit obvious oxygen octahedral tilt. The oxygen octahedral tilt increased gradually from the domain wall to the inner place of the nanodomain, indicating a regional consistency, which results in enhancement of the relaxor performance and stain property. This study opens exciting opportunities to the design of relaxor ferroelectrics with large strain for high-displacement actuator applications.

One-Stage Hydrothermal Growth and Characterization of Epitaxial LaMnO3 Films on SrTiO3 Substrate.

Epitaxial LaMnO3 thin films were grown on SrTiO3 substrate using a one-stage hydrothermal route from La(NO3)3, MnCl2 and KMnO4 in an aqueous solution of 10 M KOH at 340 °C. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) indicate full coverage of LaMnO3 on the substrate. X-ray diffraction in the symmetric ω/2θ mode suggests the film has an out-of-plane preferred orientation along the [001] direction of the substrate. The LaMnO3 epitaxial thin film growth mechanism is proposed based on the analysis of the atomic sharp interface formed between LaMnO3 and the SrTiO3 substrate, as seen by aberration-corrected scanning transmission electron microscopy (AC-STEM) imaging in combination with electronic energy loss spectroscopy (EELS). Compared with the conventional vapor deposition methods, the one-stage hydrothermal route opens up a new way to fabricate complex oxide epitaxial heterostructures.

Influence of Carbon Source on Microstructural and Mechanical Properties of High-Performance Reaction-Bonded Silicon Carbide.

Reaction-bonded silicon carbide (RBSC) has become an important structural ceramic with the benefit of being capable of preparing complex-shaped products. In order to fabricate high-performance RBSC, particle gradation of raw SiC combined with slip casting was used to prepare the porous preform before liquid silicon infiltration (LSI). The microstructural and mechanical properties of RBSC were compared by adding different amounts of carbon black (CB) content from 4 wt% to 10 wt%. Two pore structures with submicron and nano pores formed in the preform. As the amounts of carbon black increased, the mechanical properties improved and then suddenly weakened due to residual silicon initiating a nonuniform microstructure. The elastic modulus of the preform with 8 wt%CB after LSI was 389 ± 4 GPa and the flexural strength was 340 ± 17 MPa, which improved by about 150% compared to other rapid prototyping methods and has attractive application prospects.

Nitrogen migration in products during the microwave-assisted hydrothermal carbonization of spirulina platensis.

Nitrogen has a vital influence on the properties of the microwave-assisted hydrothermal carbonization (MHTC) products of Spirulina platensis (SP). The effects of hydrothermal temperature (140-220 °C) and time (1-4 h) on the product distribution and nitrogen migration of SP in MHTC were studied. Increasing temperature led to an increase in the carbon content, and a decrease in the nitrogen content in hydrochar. Protein-N was the major nitrogen-containing species in hydrochar. The total nitrogen in liquid phase increased significantly with increasing temperature. Carbon dots were found to be one of the valuable products in the liquid phase. Higher temperatures improved the amine-N level and reduced the quaternary-N content in carbon dots. A close correspondence was found between the N-containing species and the luminescence centers of carbon dots. A possible nitrogen migration mechanism was proposed to provide guidance for the potential application of the products.

Enhanced thermoelectric performance in polymorphic heavily Co-doped Cu2SnS3 through carrier compensation by Sb substitution.

Heavily acceptor-doped Cu2SnS3 (CTS) shows promisingly large power factor (PF) due to its rather high electrical conductivity (σ) which causes a modest ZT with a high electronic thermal conductivity (κe ). In the present work, a strategy of carrier compensation through Sb-doping at the Sn site in Cu2Sn0.8Co0.2S3 was investigated, aiming at tailoring electrical and phonon transport properties simultaneously. Rietveld analysis suggested a complex polymorphic microstructure in which the cation-(semi)ordered tetragonal phase becomes dominant over the coherently bonded cation-disordered cubic phase, as is preliminarily revealed using TEM observation, upon Sb-doping and Sb would substitute Sn preferentially in the tetragonal structure. With increasing content of Sb, the σ was lowered and the Seebeck coefficient (S) was enhanced effectively, which gave rise to high PFs maintained at ~10.4 µWcm-1K-2 at 773 K together with an optimal reduction in κe by 60-70% in the whole temperature range. The lattice thermal conductivity was effectively suppressed from 1.75 Wm-1K-1 to ~1.2 Wm-1K-1 at 323 K while maintained very low at 0.3-0.4 Wm-1K-1 at 773 K. As a result, a peak ZT of ~0.88 at 773 K has been achieved for Cu2Sn0.74Sb0.06Co0.2S3, which stands among the tops so far of the CTS-based diamond-like ternary sulfides. These findings demonstrate that polymorphic microstructures with cation-disordered interfaces as an approach to achieve effective phonon-blocking and low lattice thermal conductivity, of which further crystal chemistry, microstructural and electrical tailoring are possible by appropriate doping.

Significant Optimization of Electron-Phonon Transport of n-Type Bi2O2Se by Mechanical Manipulation of Se Vacancies via Shear Exfoliation.

Very recently, a novel layered oxyselenide Bi2O2Se has attracted much attention as a promising n-type eco-friendly thermoelectric material, especially for the n-type counterpart of p-type BiCuSeO. However, very poor electrical conductivity of intrinsic polycrystalline Bi2O2Se prohibits the further development of its thermoelectric performance. In the present work, a novel and facile method using a kitchen blender was developed for large-scale production of Bi2O2Se nanosheets. The electrical transport behavior of the resultant bulk Bi2O2Se via shear exfoliation changes from semiconductivity to metallic, electrical conductivity, which is greatly improved by more than 3 orders of magnitude from 0.1 to 470 S cm-1 at room temperature. Besides, thermal conductivity had been reduced to 0.93 W K-1 m-1 at 773 K. This synergistical promotion of electron-phonon transport could mainly come from increased interfacial defects of shear-exfoliated Bi2O2Se to introduce a large amount of electrons by Se vacancies and induce the intensive scattering of phonons by vacancies and interfaces. A high ZTpeak of 0.5 at 793 K had been achieved for Bi2O2Se with shear exfoliation for 60 min, which is 1.5 times larger than the ZT record of Bi2O2Se-based thermoelectrics. In addition, the figure of merit for the thermoelectric module based on p-type BiCuSeO and n-type Bi2O2Se has been evaluated to be around 0.8 at 793 K, making BiCuSeO-Bi2O2Se module a very promising candidate for mid-temperature thermoelectric applications.

Ordered Porous Poly(ionic liquid) Crystallines: Spacing Confined Ionic Surface Enhancing Selective CO2 Capture and Fixation.

Porous poly(ionic liquid)s (PPILs) combine the features of porous materials, polymers, and ionic liquids (ILs) or their derivatives, but they are normally of amorphous structure with disordered pores. Here, we report the facile synthesis of ordered porous poly(ionic liquid) crystallines (OPICs, specialized as a kind of PPIL analogues) with diverse and adjustable framework IL moieties through the Schiff base condensation of IL-derived ionic salts and neutral monomers. Ternary monomer mixtures are employed to artistically control the chemical composition and pore configurations. Compact atomic packing was achieved to give spacing confined ionic surface with strong CO2 affinity. Through monomer control, OPICs exhibit high CO2 uptakes with excellent CO2/N2(CH4) selectivities and efficiently implement CO2 fixation through catalyzing epoxides cycloaddition under down to ambient conditions.