Fabrication and properties of pressure-sintered reaction-bonded Si3N4 ceramics with addition of Eu2O3–MgO–Y2O3

Dense pressure-sintered reaction-bonded Si₃N₄ (PSRBSN) ceramics were obtained by a hot-press sintering method. Precursor Si powders were prepared with Eu₂O₃–MgO–Y₂O₃ sintering additive. The addition of Eu₂O₃–MgO–Y₂O₃ was shown to promote full nitridation of the Si powder. The nitrided Si₃N₄ particles had an equiaxial morphology, without whisker formation, after the Si powders doped with Eu₂O₃–MgO–Y₂O₃ were nitrided at 1400 °C for 2 h. After hot pressing, the relative density, Vickers hardness, flexural strength, and fracture toughness of the PSRBSN ceramics, with 5 wt% Eu₂O₃ doping, were 98.3 ± 0.2%, 17.8 ± 0.8 GPa, 697.0 ± 67.0 MPa, and 7.3 ± 0.3 MPa m^1/2, respectively. The thermal conductivity was 73.6 ± 0.2 W m^?1 K^?1, significantly higher than the counterpart without Eu₂O₃ doping, or with ZrO₂ doping by conventional methods.     

Pseudocapacitive contributions to electrochemical kinetics in NiOx electrochromic anodes

Because of its ability to change optical absorption dynamically by applied electric field, nickel oxide (NiO) is a promising anodic material in smart windows, which can improve energy conversion efficiency in construction buildings. Although many works have achieved high electrochromic performance with different method. The underlying mechanism is still not fully investigated. In this article, we prepared the NiO films with large specific surface area and high stability by electron beam evaporation. X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to figure out the surface morphology and composition of as-deposited films. Afterwards, the electrochemical properties and optical performance of the prepared NiO films were investigated. On this basis, the origin of surface charge was fully analyzed by cyclic voltammetry and diffusion coefficient test. These experimental and theoretical results firmly confirm that both the surface reaction and capacitive effect bring about the excellent EC performance in NiO films. These results not only provide clear evidence about electrochemical kinetics in NiO films, but also offer some useful guidelines for the design of EC materials with higher performance and longer stability.     

Matrix Manipulation of Directly-Synthesized PbS Quantum Dot Inks Enabled by Coordination Engineering

The direct-synthesis of conductive PbS quantum dot (QD) ink is facile, scalable, and low-cost, boosting the future commercialization of optoelectronics based on colloidal QDs. However, manipulating the QD matrix structures still is a challenge, which limits the corresponding QD solar cell performance. Here, for the first time a coordination-engineering strategy to finely adjust the matrix thickness around the QDs is presented, in which halogen salts are introduced into the reaction to convert the excessive insulating lead iodide into soluble iodoplumbate species. As a result, the obtained QD film exhibits shrunk insulating shells, leading to higher charge carrier transport and superior surface passivation compared to the control devices. A significantly improved power-conversion efficiency from 10.52% to 12.12% can be achieved after the matrix engineering. Therefore, the work shows high significance in promoting the practical application of directly synthesized PbS QD inks in large-area low-cost optoelectronic devices.     

Spectroscopic properties and thermally stable orange-red luminescence of Sm:Zr:LiNbO3 and Sm:Hf:LiNbO3 for white LED applications

LiNbO₃ crystals activated by Sm³⁺ and co-doped with Zr⁴⁺ (Sm:Zr:LN) or Hf⁴⁺ (Sm:Hf:LN) were prepared by the Czochralski method. Detailed investigation on spectroscopic properties was conducted on the frame of Judd-Ofelt (J-O) theory. The J-O intensity parameters Ω_i (i = 2, 4, 6), fluorescence branching ratios and radiative lifetime of excited level ⁴G_5/2 were determined. Furthermore, the thermal stability of the strong orange-red emissions obtained under near-UV excitation in both crystals was evaluated. As high as 100% and 97% of integrated intensities at room temperature in Sm:Zr:LN and Sm:Hf:LN respectively were retained at 423 K, demonstrating the suppressed thermal attenuation. The temperature sensing performance based on fluorescence intensity ratio strategy was degraded at higher temperatures with relatively low sensitivities, while the shift of CIE chromaticity coordinates of Sm:Zr:LN and Sm:Hf:LN in the orange-red region was insignificant, demonstrating the color constancy with increasing temperature. With the efficient and thermally stable orange-red luminescence, Sm:Zr:LN and Sm:Hf:LN could serve as promising candidate materials for near-UV excited white light-emitting diodes.     

Sounds Stimulation on In Vitro HL1 Cells: A Pilot Study and a Theoretical Physical Model

Mechanical vibrations seem to affect the behaviour of different cell types and the functions of different organs. Pressure waves, including acoustic waves (sounds), could affect cytoskeletal molecules via coherent changes in their spatial organization and mechano-transduction signalling. We analyzed the sounds spectra and their fractal features. Cardiac muscle HL1 cells were exposed to different sounds, were stained for cytoskeletal markers (phalloidin, beta-actin, alpha-tubulin, alpha-actinin-1), and studied with multifractal analysis (using FracLac for ImageJ). A single cell was live-imaged and its dynamic contractility changes in response to each different sound were analysed (using Musclemotion for ImageJ). Different sound stimuli seem to influence the contractility and the spatial organization of HL1 cells, resulting in a different localization and fluorescence emission of cytoskeletal proteins. Since the cellular behaviour seems to correlate with the fractal structure of the sound used, we speculate that it can influence the cells by virtue of the different sound waves’ geometric properties that we have photographed and filmed. A theoretical physical model is proposed to explain our results, based on the coherent molecular dynamics. We stress the role of the systemic view in the understanding of the biological activity.     

珠江口盆地珠一坳陷古近系高自然伽马砂岩形成机制及油气地质意义

运用放射性元素寻找油气是一种非常规油气勘探手段。近年来,在珠江口盆地珠一坳陷富烃凹陷周边古近系钻遇高自然伽马(GR)砂岩,其GR值(100~300 API)甚至大于同区泥岩的GR值(100~200 API)。为了弄清该特殊现象背后的地质意义,对珠江口盆地珠一坳陷古近系高自然伽马砂岩开展了铀(U)、钍(Th)、钾(K)等3种元素含量与GR值的相关趋势线分析,从井震特征、岩性特征及矿物成分特征等入手分析了砂岩GR值增高的主要原因及成因机制,探讨了放射性元素聚集的条件、运移通道、驱动力以及油气意义。结果表明:西江、惠州地区由U含量增高导致砂岩GR值偏高,恩平、番禺地区由K,Th含量增高导致砂岩GR值偏高;砂岩GR值增高有两大成因机制,一是地下流体带来的放射性元素离子U4+在氧化-还原面处富集后导致地层GR值偏高,这种特殊现象说明在具有连通基底大断裂旁的圈闭中,U4+的富集指示了曾经油气的存在,证实了研究区油气运移通道的有效性,对于油气藏的预测有着非常重要的指导性意义,二是地表流体带来的含放射性元素的矿物大量沉积后导致地层GR值偏高,含放射性元素矿物性质不稳定,可指示近源供给的存在,对于判断物源及沉积环境有着非常重要的意义。该研究成果为预测研究区油气成藏有利区带提供了依据。     

Freeze-drying and mechanical redispersion of aqueous PEDOT:PSS

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films are attracting famous applications in antistatic coating, energy storage and conversion, printed electronics, and biomedical fields due to their conductivity, optical transparency and flexibility. However, PEDOT:PSS has poor dispersion stability during long-term storage and transport. Moreover, the dried PEDOT:PSS films are insoluble in any solvent and cannot be redispersed again. In comparison to bake drying, here, a feasible strategy to achieve mechanically redispersed PEDOT:PSS with the help of freeze-drying process was reported. The redispersed PEDOT:PSS can recover not only the initial characters such as pH, chemical composition, viscosity, and particle size under similar solid contents, but also conductivity and surface morphology of treated films. In addition, the treated film exhibits self-healing properties similar to pristine film in terms of mechanical and electrical properties. This technology enables reuse and overcomes the technical problems of PEDOT:PSS dispersion, realizing real-time processing to meet variable applications.     

Phase,domain, and microstructures in Sr2+ substituted low-temperature sintering PZT-based relaxor ferroelectrics

The Ag-Pd internal electrode of multilayer piezoelectric ceramics needs to be sintered below 1000°C, and lead wires and components need to be welded with lead-free solder at 260°C. PNN–PMW–PZT–xSr piezoelectric ceramics with high Curie temperature (T_c > 260°C) were synthesized at a low sintering temperature (960°C) to meet the requirements of multilayer piezoelectric devices. The relationship between structures (phase, domain, and microstructures) and electrical properties (piezo/ferroelectric properties, and dielectric relaxation) in the Sr²⁺ substituted ceramics was investigated. Rietveld refinement and Raman spectra show that Sr²⁺ substitution can cause the phase change and increase the force constant of [BO₆] octahedron. The piezoelectric response increases with increasing the content of the tetragonal phase (CTP) in the rhombohedral-tetragonal (R-T) coexisted ceramics. The ceramics with 0.6 mol% Sr²⁺ substitution have minimum activation energy for domain wall movement (E_a) of 0.0362 eV which favors the formation of nanometer-sized domains, and possess excellent electrical properties (d₃₃ = 623 pC/N, d₃₃^* =783 pm/V, T_c =295°C). The higher the CTP, the lower the E_a. The lower E_a favors the rotation of polarization direction and extension, and is beneficial to the generation of the nanometer-size domains, resulting in high piezoelectric properties.