Size effect on Debye temperature of metal crystals.

Understanding the physical origin of materials exhibiting different properties at the mesoscale is of great significance for the design and fabrication of multifunctional quantum devices. In this work, we proposed a simple model without any adjustable parameters to describe the size (D) dependence of Debye temperature ΘD(D) of metallic nanocrystals. ΘD(D) drops with the decrease of D, which is verified by relevant experimental and simulation results. In addition, we found that the difference in the size dependence of ΘD(D) of different metal elements is determined by the ratio of the solid/liquid interface energy γsl and surface stress f, and the smaller the D of the nanocrystals, the greater the influence of γsl/f on ΘD(D)/ΘD.

Balanced Mechanical and Biotribological Properties of Polymer Composites Reinforced by a 3D Interlocked Si3N4 Nanowire Membrane.

Polymer composites have great potential applications in the hip joint replacement, where the combinations of high mechanical strength and excellent biotribological properties are required. In this work, a well-dispersed three-dimensional (3D) silicon nitride nanowire membrane (SNm) designed as a reinforcement and brushite (Bs) served as bioactive filler are constructed into the polymer matrix, forming SNm-reinforced Bs/polymer composites (SNm-Bs/Pm). Especially, SNm could form a 3D interlocked structure, where the ultralong silicon nitride nanowires are entangled with each other. SNm could effectively facilitate the penetration of the polymer matrix and improve the cohesion strength of the polymer, thereby promoting mechanical and biotribological properties for SNm-Bs/Pm. The performances for polymer composites are optimized by increasing the layer number of preform. By comparing SNm-Bs/Pm with one-layer preform, the tensile strength of SNm-Bs/Pm with six-layer preforms reaches 83.3 MPa with an increase of 767.7%. In addition, the friction coefficient and wear rate of SNm-Bs/Pm with six-layer preforms in fetal bovine serum medium achieve 0.06 and 0.21 × 10-14 m3(N·m)-1 and decrease by 82.4 and 72.4%, respectively. The present work provides a promising methodology of preparing interlocked SNm-reinforced polymer composites with enhanced mechanical and biotribological properties that are potential for hip joint replacement applications.

Interfacial melting mechanism of nanocrystals determined by interfacial energy and interfacial stress.

To clarify the interface melting mechanism, a unified analytical expression was developed to describe the depression and superheating of Tm(D) functions for metallic nanoparticles, nanostructures, and nanoparticles embedded in a coherent or incoherent interface. Tm(D) functions are determined by the sign of γss, fss (or γsl and fsl), and D0 as caused by the change of interface environments. We found that there is TCIm(D) > TNSm(D) > TIIm(D) > TNPsm(D) for Ag nanocrystals within different interfaces. Moreover, for a given size, Tm(D)/Tm(∞) decreases with the reduction of γss/fss for nanoparticles, nanostructures and nanoparticles embedded in incoherent interfaces, while an opposite trend occurs for the coherent interfaces. In addition, we also found that there is TNPsm(D)/Tm(∞) < TIIm(D)/Tm(∞) < TNSm(D)/Tm(∞), which is in agreement with the relation of γNPssl/fNPssl < γIIss/fIIss < γNSss/fNSss. By analyzing the γss(D) (or γsl(D)), fss(D) (or fsl(D)) and γss(D)/fss(D) (or γsl(D)/fsl(D)) functions of Ag nanocrystals and comparing with their Tm(D) functions, it is found that there is a high consistency between the variation of γss(D)/fss(D) (γsl(D)/fsl(D)) and Tm(D)/Tm, which reveals that the size dependence of Tm(D)/Tm is determined by γss(D)/fss(D) (or γsl(D)/fsl(D)). Our predictions show a good agreement with the available theoretical and experimental results.

SiC Nanowire-Si3N4 Nanobelt Interlocking Interfacial Enhancement of Carbon Fiber Composites with Boosting Mechanical and Frictional Properties.

Carbon fiber composites composed of carbon fiber and pyrolytic carbon (PyC) matrix have great potential application in the brakes of aircrafts, where the combination of high mechanical strength and excellent frictional properties are required. In this work, two-component silicon-based interlocking enhancements were designed and constructed into carbon fiber composites for boosting the mechanical and frictional properties. Specially, silicon carbide nanowires (SiCnws) and silicon nitride nanobelts (Si3N4nbs) could form interlocking architectures, where SiCnws are rooted firmly on the carbon fiber surface in the radial direction and Si3N4nbs integrate the PyC matrix with carbon fibers together via a networked shape. SiCnws-Si3N4nbs not only refine the PyC matrix but also promote the bonding of the fiber/matrix interface and the cohesion strength of the PyC matrix, thus enhancing the mechanical and frictional properties. Benefiting from the SiCnws-Si3N4nbs synergistic effect and interlocking enhancement mechanism, the interlaminar shear strength and compressive strength of carbon fiber composites increased by 88.41% and 73.40%, respectively. In addition, the friction coefficient and wear rate of carbon fiber composites decreased by 39.50% and 69.88%, respectively. This work could open up an interlocking enhancement strategy for efficiently fabricating carbon fiber composites and promoting mechanical and frictional properties that could be used in the brakes of aircrafts.

Ultrasound-induced liquid/solid interfacial reaction between Zn-3Al alloy and Zr-based bulk metallic glasses.

Ultrasound-assisted fluxless brazing of Zr based Bulk metallic glasses (Zr-BMG) joint using Zn-3Al filler metal was performed in this study. The effect of ultrasonic vibration time on the microstructure and mechanical properties of Zr-BMG joints were investigated. Results showed that excellent metallurgic bonding could be obtained in ultrasonically brazed Zr-BMG joints. The interfacial reaction between liquid Zn-3Al filler metal and Zr-BMG substrate showed a mutation characteristic, which could be distinguished into incubation period and acceleration period. In the incubation period, Zn50Zr25Al25 intermetallic compounds (IMCs) with small ellipsoidal shape were slowly formed and distributed randomly on Zr-BMG surface. However, in the acceleration period, Zn50Zr25Al25 ellipsoids developed rapidly into a wavy-structured IMCs layer with a thickness of 17 µm, which was comprised of alternate Zn50Zr25Al25 and Zn22Zr sublayers. The microstructure evolution of Zn-3Al/Zr-BMG interface was ascribed to the combined effects of acoustic cavitations and Al element controlled interfacial metallurgic reactions. The average shear strength of joint was increased firstly then decreased slightly with increasing ultrasonic vibration time, and a highest strength value of approximately 100 MPa was obtained for joints brazed for 96 s. The shearing failure was inclined to occur at the Zn-3Al/Zr-BMG interface then transferred into the interfacial IMCs layer with increasing ultrasonic vibration time.

Tunable CsPbBr3/Cs4PbBr6 phase transformation and their optical spectroscopic properties.

As a novel type of promising materials, metal halide perovskites are a rising star in the field of optoelectronics. On this basis, a new frontier of zero-dimensional perovskite-related Cs4PbBr6 with bright green emission and high stability has attracted an enormous amount of attention, even though its photoluminescence still requires to clarification. Herein, the controllable phase transformation between three-dimensional CsPbBr3 and zero-dimensional Cs4PbBr6 is easily achieved in a facile ligand-assisted supersaturated recrystallization synthesis procedure via tuning the amount of surfactants, and their unique optical properties are investigated and compared in detail. Both Cs4PbBr6 and CsPbBr3 produce remarkably intense green luminescence with quantum yields up to 45% and 80%, respectively; however, significantly different emitting behaviors are observed. The fluorescence lifetime of Cs4PbBr6 is much longer than that of CsPbBr3, and photo-blinking is easily detected in the Cs4PbBr6 product, proving that the zero-dimensional Cs4PbBr6 is indeed a highly luminescent perovskite-related material. Additionally, for the first time, tunable emissions over the visible-light spectral region are demonstrated to be achievable via halogen composition modulations in the Cs4PbX6 (X = Cl, Br, I) samples. Our study brings a simple method for the phase control of CsPbBr3/Cs4PbBr6 and demonstrates the intrinsic luminescence nature of the zero-dimensional perovskite-related Cs4PbX6 products.

Conducting polymer-coated MIL-101/S composite with scale-like shell structure for improving Li-S batteries.

Lithium-sulfur batteries are regarded as a promising energy storage system. However, they are plagued by rapid capacity decay, low coulombic efficiency, a severe shuttle effect and low sulfur loading in cathodes. To address these problems, effective carriers are highly demanded to encapsulate sulfur in order to extend the cycle life. Herein, we introduced a doped-PEDOT:PSS-coated MIL-101/S multi-core-shell structured composite. The unique structure of MIL-101, large specific area and conductive shell ensure high dispersion of sulfur in the composite and minimize the loss of polysulfides to the electrolyte. The doped-PEDOT:PSS-coated sulfur electrodes exhibited an increase in initial capacity and an improvement in rate characteristics. After 192 cycles at the current density of 0.1C, a doped-PEDOT:PSS-coated MIL-101/S electrode maintained a capacity of 606.62 mA h g-1, while the MIL-101/S@PEDOT:PSS electrode delivered a capacity of 456.69 mA h g-1. The EIS measurement revealed that the surface modification with the conducting polymer provided a lower resistance to the sulfur electrode, which resulted in better electrochemical behaviors in Li-S battery applications. Test results indicate that the MIL-101/S@doped-PEDOT:PSS is a promising host material for the sulfur cathode in the lithium-sulfur battery applications.