Science and Technology of Advanced Materials最新文献

Full-Heusler compounds represent a rich and diverse class of functional materials, covering a large compositional phase space. Representatives with 24 valence electrons are commonly semimetals or narrow-gap semiconductors as per the Slater-Pauling rule and are thus considered as thermoelectric materials, especially for room-temperature applications. Research on the archetypal thermoelectric full-Heusler compound Fe₂VAl began over two decades ago, and since then, significant progress has been made in enhancing its thermoelectric performance. Advances have been achieved through various intrinsic and extrinsic substitutions, grain boundary engineering and other optimization strategies. Here, recent advancements are reviewed, challenges for the further development of competitive full-Heusler thermoelectrics are identified, and novel routes and concepts are highlighted that could make these materials viable for energy harvesting and cooling applications near room-temperature.

Solvent-free alkyl-π liquids, an emerging class of optoelectronically-active soft materials, have attracted attention for their applications in soft electronics, offering liquid fluidity as well as predictable and stable π-functions. Extensive research has been conducted to date on controlling the optoelectronic properties of alkyl-π liquids. When modulating function by adding solid dopants, the dopant molecules have poor solubility, leading to insoluble aggregates and inconsistencies in properties such as luminescent color. Chemical modification of the π-skeleton requires synthesizing molecules that display the desired properties, which poses challenges in achieving predictable performance and ensuring economic feasibility across various molecular designs. In this study, we propose a liquid-liquid blending strategy that enables the precise and homogeneous merge of π-functions of alkyl π-liquids. Rheological analysis was used to evaluate miscibility between alkyl π-liquids. Furthermore, the accurate and uniform control of the photoluminescent color--a representative π-function--was successfully demonstrated through the blending of three alkyl π-liquids that emit the three primary colors. This liquid-liquid blending strategy offers an innovative approach for adjusting not only luminescent color but also for merging various π-functions in solvent-free liquid materials.

Materials with magnetic anisotropy can serve as a model object for exploring the multicaloric effect because their thermodynamic state alterations can be achieved either through the application of a magnetic field H or/and by mechanically rotating the sample in the magnetic field using torque τ. In such materials, the total entropy change $\Delta S_T$ arises from two distinct contributions: (1) the conventional magnetocaloric effect (MCE) or paraprocess $\Delta S_{\left(m\right)}$ and (2) the rotational MCE $\Delta S_{\phi }$ . In this manuscript, using molecular field model which enables a separation of contributions to the total entropy change $\Delta S_T$ from conventional $\Delta S_{\left(m\right)}$ and rotational $\Delta S_{\phi }$ , we have determined cross-coupling multicaloric coefficients ${\chi }_{\tau ,H}={\left(\frac{\mathrm{\partial \tau }}{\mathrm{\partial H}}\right)}_{T,\theta }$ and ${\chi }_{H,\tau }=-{\left(\frac{\mathrm{\partial m}}{\mathrm{\partial \theta }}\right)}_{T,H}$ for anisotropic magnetic materials and show that they satisfy the basic thermodynamic identities. We also confirmed that the total multicaloric effect in the material with magnetic anisotropy can be accurately expressed as the sum of the individual magnetocaloric effects induced by separate application of the H and τ, minus the magnetic entropy change arising from thermodynamic cross-coupling between the subsystems of the solid: $\hspace{0.17em}\Delta S_T=\Delta S_{T,\tau }^{\left(H\right)}+\Delta S_{T,H}^{\left(\theta \right)}-\hspace{0.17em}\Delta S_{\mathrm{coupling}}$ .

High-performance thermoelectric (TE) materials near room temperature are crucial for cooling and energy harvesting applications. This study reports the outstanding thermoelectric performance of p-type Mn-doped Fe₂VAl Heusler alloy thin films, specifically Fe₂V_0.8Mn_0.2Al, prepared using magnetron sputtering. These films were deposited on insulating oxide substrates to eliminate any spurious contributions from the substrate. Large p-type Seebeck coefficients (S) have been observed for all films, revealing a maximum power factor of 4.26 mWK^-2m^-1 at 300 K. This study revealed thickness-dependent thermoelectric properties, with the highest power factor achieved in the 500 nm film. Films with d = 300 nm and 500 nm exhibit weak ferromagnetism. Hall resistivity measurements evidence an anomalous Hall effect (AHE) for the 300 nm and 500 nm samples. The AHE is strongest for the 500 nm film, consistent with a magnetic enhancement of the Seebeck coefficient and power factor. Additionally, we synthesized Al-rich p-type Fe₂V_0.9Mn_0.1Al_1.5 thin films at room temperature, 200°C, 400°C, and 600°C. The film deposited at 600°C exhibits an exceptional figure of merit ZT _appr ~0.8 and a power factor of 6.7 mW·K^-2·m^-1 at room temperature, which are respectively, 4 times and 1.5 times larger than the best values ever reported for any bulk or thin film p-type Fe₂VAl-based material.

Open systems on the surfaces of soft materials induce dissipative structures such as evaporative self-organization. Based on the viscous fingering phenomena, we demonstrate a meniscus splitting phenomena by evaporating an aqueous solution of versatile polyvinyl alcohol (PVA) solution from a Hele-Shaw cell. To understand it as a universal phenomenon independent of the polymer species, the distinct evolutionary pathways to pattern formation were evaluated, focusing on the interface deformation and directional deposition of the polymer. The PVA solution, which showed a steep concentration-dependent viscosity gradient under a local moderate humidity gradient, was capable of bridging the cell gap for vertical membrane formation. The interfacial shape transformation from one downward concave to multiple upward convex shapes is controllable not only by tuning the physical properties of the polymer but also by conditioning the water evaporating atmosphere. We envision that demonstrations with different cell aperture designs will expand the realization of this phenomenon using other synthetic polymers or chemical species. Such an open system design with humidity tuning is a strategy for exposure to non-equilibrium phenomena using various soft materials, particles, fibers, and networks.

Micro-particles with an internal helical liquid crystalline (LC) molecular order serve as efficient and highly compact circularly polarized luminescence (CPL) emitters. However, the coupling between CPL emission and the interior LC molecular order remains poorly understood at the single particle level. Here, we synthesized microspheres from an LC monomer RM23 together with a fluorescent dye and a chiral additive (R/S-BPy) and investigated their CPL properties. Polarized optical microscopy and angle-dependent CPL observations at a single-particle level revealed randomly distributed one-handed helical domains in each sphere, leading to CPL emission with an average dissymmetry factor value |g _lum| of 0.05 regardless the observation angle. The color of the CPL emission is tunable in the range of 450-700 nm by varying the fluorescent dyes doped in the spheres.

We utilized twin network analysis of polycrystalline materials through graph theory to visualize microstructures and examine the behavior of dislocation cluster generation in multicrystalline silicon grown by directional solidification. This approach allows for a rapid and statistical understanding of microstructures and their correlations by representing these features and their changes as network graphs. Our analysis revealed that dislocation clusters are formed at asymmetric Σ27a grain boundaries, which result from a specific twinning process. Gaining this knowledge is expected to assist in identifying grain boundary groups that can minimize the formation of dislocation clusters.

Influences of the stacking sequence and in-plane ordering of Zn₆Y₈ atomic clusters on the basal slip in long-period stacking-ordered (LPSO) phases in the Mg-Zn-Y systems were investigated by micropillar compression of single crystals at room temperature. The critical resolved shear stress (CRSS) values for basal slip do not depend much on the stacking sequence of the LPSO structures and the degree of the in-plane ordering of Zn₆Y₈ atomic clusters. The CRSS values increase with the decrease in the specimen size, following an inverse power-law relationship with a very large power-law exponent of about 0.88. Atomic-resolution scanning transmission electron microscopy (STEM) imaging of core structures of basal edge dislocations in the Mg-Zn-Y LPSO phase with a perfect in-plane ordering of Zn₆Y₈ atomic clusters revealed that the Burgers vector is b = (a/3)[2 $\stackrel{-}{1}$ $\stackrel{-}{1}$ 0] and the basal dislocations glide between the atomic planes which do not cut through Zn₆Y₈ atomic clusters.

YbMnSb₂, a topological semimetal with an exotic band structure, has recently been found to exhibit potential thermoelectric transport properties in its single-crystalline formality. The fabrication of polycrystals, which have the advantages of easy synthesis and doping tunability, will advance the transport studies of YbMnSb₂ but face challenges. Here, we found that the polycrystalline YbMnSb₂, synthesized using the conventional melting method, unexpectedly exhibits obvious impurities due to the competing phase YbMn₂Sb₂. To avoid the high-temperature synthesis, high-quality polycrystalline bulk YbMnSb₂, as well as three other RMnSb₂ (R = Sr, Ba, Eu), were successfully prepared by mechanical alloying followed by spark plasma sintering. Based on the high-quality polycrystalline samples, it was discovered that YbMnSb₂ reacts with oxygen during heating in the presence of small amounts of oxygen, resulting in MnSb, Yb₂O₃, and Sb. A similar oxidation phenomenon also occurs for the other RMnSb₂. This work provides a feasible method for synthesizing high-quality RMnSb₂ polycrystals, which should also be suitable for the other isostructural topological semimetals, paving the way for future studies of their transport properties.

Carbon materials with ordered frameworks and atomically dispersed metal sites, referred to as ordered carbonaceous frameworks (OCFs), have attracted considerable attention for their promising potential in fundamental research and diverse practical applications, particularly in electrocatalysis. In this work, we synthesize Fe-incorporated OCF (Fe-OCF) with a heme-like structure through structure-preserving pyrolysis of Fe-porphyrin with four ethynyl groups. Fe-OCF is characterized by its ordered microporous framework, incorporating atomically dispersed Fe(III) sites with a high content of 6.9 wt%, analogous to metal-organic frameworks. At the same time, Fe-OCF possesses the advantages of carbon materials, including chemical stability, thermal stability, and electrical conductivity. Remarkably, Fe-OCF mimics the functionality of a sensor enzyme by facilitating the redox reaction of hydrogen peroxide, which is regulated by an applied potential, thereby enabling bidirectional catalytic behavior. Fe-OCF exhibits a linear reduction current response to hydrogen peroxide, underscoring its efficient electron transfer and catalytic properties. Moreover, Fe-OCF demonstrates superior stability compared to molecular Fe-porphyrin, further emphasizing its potential application as a novel hydrogen peroxide sensor. These results emphasize the significant potential of Fe-based OCFs as advanced materials for artificial enzyme applications and next-generation hydrogen peroxide sensing technology.