SnTe thermoelectric materials with low lattice thermal conductivity synthesized by a self-propagating method under a high-gravity field.

The conventional fabrication methods (for example, melting and powder metallurgy) of bulk thermoelectric materials are time- and energy-consuming, which restrict their large-scale application. In this work, ultra-fast self-propagating synthesis under a high-gravity field was used to prepare SnTe bulks, which shortened the synthesis time from several days to a few seconds. The grain growth was suppressed and some small pores were reserved in the matrix during the ultra-fast solidification process. The increased grain boundaries and pores (nanoscale to micron scale) enhanced phonon scattering, which greatly decreased the lattice thermal conductivity. The obtained minimum lattice thermal conductivity is 0.81 W m-1 K-1, and the maximum zT value is 0.5 (873 K), which is comparable to the best reported results of the undoped SnTe alloy. The ultra-fast non-equilibrium synthesis technique opens up new possibilities to prepare high-efficiency bulk thermoelectric materials with reduced time and energy consumption.

Correlation of Tunable CoSi4 Tetrahedron with the Superconducting Properties of LaCoSi.

It is known that as the FeAs4 tetrahedron in the Fe-based superconductor is close to the regular tetrahedron, critical temperature (Tc) can be greatly increased. Recently, a Co-based superconductor of LaCoSi (4 K) with "111" structure was found. In this work, we improve the Tc of LaCoSi through structural regulation. Tc can be increased by the chemical substitution of Co by Fe, while the superconductivity is suppressed by the Ni substitution. The combined analysis of neutron and synchrotron X-ray powder diffractions reveals that the change of the Si-Co-Si bond angles of the CoSi4 tetrahedron is possibly responsible for the determination of superconducting properties. The Fe chemical substitution is favorable for the formation of the regular tetrahedron of CoSi4. The present new Co-based superconductor of LaCoSi provides a possible method to enhance the superconductivity performance of the Co-based superconductors via controlling Co-based tetrahedra similar to those well established in the Fe-based superconductors.

Superconductivity in Co-Layered LaCoSi.

It is known that few Co-based superconducting compounds have been found compared with their Fe- or Ni-based counterparts. In this study, we have found superconductivity of 4 K in the LaCoSi compound for the first time. The combined analysis of neutron and synchrotron X-ray powder diffractions reveals that LaCoSi exhibits an isostructure with the known Fe-based LiFeAs superconductor, which is the first "111" Co-based superconductor. First-principles calculation shows that LaCoSi presents a quasi-two-dimensional band structure that is also similar to that of LiFeAs. The small structural distortion may be more conducive to the emergence of superconductivity in the LaCoSi compound, which provides a direction for finding new Co-based superconducting compounds.

Monitoring Strain Response of Epoxy Resin during Curing and Cooling Using an Embedded Strain Gauge.

The present work describes the monitoring system of the real-time strain response on the curing process of epoxy resin from the initial point of curing to the end, and the change in strain during temperature changes. A simple mould was designed to embed the strain gauge, thermometer, and quartz standard sample into the epoxy resin, so that the strain and the temperature were simultaneously measured and recorded. A cryogenic-grade epoxy resin was tested and the Differential Scanning Calorimetry (DSC) was used to analyse the curing process. Based on the DSC results, three curing processes were adopted to investigate their influence on strain response as well as residual strain of the epoxy resin. Moreover, impact strength of the epoxy resin with various curing temperatures were tested and the results indicate that the curing plays a crucial role on the mechanical properties. The method will find cryogenic application of epoxy adhesives and epoxy resin based composites to monitor the strain during the curing process as well as the cryogenic service.

Dual-Functional Supernanoparticles with Microwave Dynamic Therapy and Microwave Thermal Therapy.

The cytotoxic reactive oxygen species (ROS) generated by photoactivated sensitizers have been well explored in tumor therapy for nearly half a century, which is known as photodynamic therapy (PDT). The poor light penetration depth severely hinders PDT as a primary or adjuvant therapy for clinical indication. Whereas microwaves (MWs) are advantageous for deep penetration depth, the MW energy is considerably lower than that required for the activation of any species to induce ROS generation. Herein we find that liquid metal (LM) supernanoparticles activated by MW irradiation can generate ROS, such as ·OH and ·O2. On this basis, we design dual-functional supernanoparticles by loading LMs and an MW heating sensitizer ionic liquid (IL) into mesoporous ZrO2 nanoparticles, which can be activated by MW as the sole energy source for dynamic and thermal therapy concomitantly. The microwave sensitizer opens the door to an entirely novel dynamic treatment for tumors.

Negative Thermal Expansion in (Hf,Ti)Fe2 Induced by the Ferromagnetic and Antiferromagnetic Phase Coexistence.

Negative thermal expansion (NTE) is an intriguing physical phenomenon that can be used in the applications of thermal expansion adjustment of materials. In this study, we report a NTE compound of (Hf,Ti)Fe2, while both end members of HfFe2 and TiFe2 show positive thermal expansion. The results reveal that phase coexistence is detected in the whole NTE zone, in which one phase is ferromagnetic (FM), while the other is antiferromagnetic (AFM). With increasing temperature, the FM phase is gradually transformed to the AFM one. The NTE phenomenon occurs in the present (Hf,Ti)Fe2 because of the fact that the unit cell volume of the AFM phase is smaller than that of the FM phase, and the mass fraction of the AFM phase increases with increasing temperature. The construction of phase coexistence can be a method to achieve NTE materials in future studies.

Atomic Linkage Flexibility Tuned Isotropic Negative, Zero, and Positive Thermal Expansion in MZrF6 (M = Ca, Mn, Fe, Co, Ni, and Zn).

The controllable isotropic thermal expansion with a broad coefficient of thermal expansion (CTE) window is intriguing but remains challenge. Herein we report a cubic MZrF6 series (M = Ca, Mn, Fe, Co, Ni and Zn), which exhibit controllable thermal expansion over a wide temperature range and with a broader CTE window (-6.69 to +18.23 × 10-6/K). In particular, an isotropic zero thermal expansion (ZTE) is achieved in ZnZrF6, which is one of the rarely documented high-temperature isotropic ZTE compounds. By utilizing temperature-dependent high-energy synchrotron X-ray total scattering diffraction, it is found that the flexibility of metal···F atomic linkages in MZrF6 plays a critical role in distinct thermal expansions. The flexible metal···F atomic linkages induce negative thermal expansion (NTE) for CaZrF6, whereas the stiff ones bring positive thermal expansion (PTE) for NiZrF6. Thermal expansion could be transformed from striking negative, to zero, and finally to considerable positive though tuning the flexibility of metal···F atomic linkages by substitution with a series of cations on M sites of MZrF6. The present study not only extends the scope of NTE families and rare high-temperature isotropic ZTE compounds but also proposes a new method to design systematically controllable isotropic thermal expansion frameworks from the perspective of atomic linkage flexibility.

Cs3W3PO13: A Tungsten Phosphate with One-Dimensional Zigzag Tunnels Exhibiting Strongly Anisotropic Thermal Expansion.

A new tungsten phosphate, Cs3W3PO13, is synthesized using the high-temperature flux method. Cs3W3PO13 crystallizes in the space group Pnma and contains one-dimensional zigzag tunnels, which are found for the first time in tungsten phosphate. This highly anisotropic structural feature results in a very strong anisotropic thermal expansion, with thermal expansion coefficients of 14.15 ± 1.11 and 0.72 ± 0.22 M K(-1) along the a and b axes, respectively, over the temperature range from 13 to 270 K. In addition, thermal analysis, UV-vis-near-IR diffuse reflectance, and first-principles electronic structure calculations on Cs3W3PO13 are performed.

Effect of cobalt doping on the structural, magnetic and abnormal thermal expansion properties of NaZn13-type La(Fe1-xCox)11.4Al1.6 compounds.

Cubic NaZn13-type La(Fe1-xCox)11.4Al1.6 compounds were synthesized and extensively explored through crystal structure and magnetization analyses. By optimizing the chemical composition, the isotropic abnormal properties of excellent zero and giant negative thermal expansion in a pure form were both found at different temperature ranges through room temperature. Moreover, the temperature regions with the remarkable abnormal thermal expansion (ATE) properties have been broadened which are controlled by the dM/dT. The present study demonstrates that the ATE behavior mainly depends on special structural and magnetic properties. These diverse properties suggest the high potential of La(Fe1-xCox)11.4Al1.6 for the development of abnormal expansion materials.

Broad Negative Thermal Expansion Operation-Temperature Window Achieved by Adjusting Fe-Fe Magnetic Exchange Coupling in La(Fe,Si)13 Compounds.

Cubic La(Fe,Si)13-based compounds have been recently developed as promising negative thermal expansion(NTE) materials, but the narrow NTE operation-temperature window(∼110 K) restricts their actual applications. In this work, we demonstrate that the NTE operation-temperature window of LaFe(13-x)Si(x) can be significantly broadened by adjusting Fe-Fe magnetic exchange coupling as x ranges from 2.8 to 3.1. In particular, the NTE operation-temperature window of LaFe10.1Si2.9 is extended to 220 K. More attractively, the coefficients of thermal expansion of LaFe10.0Si3.0 and LaFe9.9Si3.1 are homogeneous in the NTE operation-temperature range of about 200 K, which is much valuable for the stability of fabricating devices. The further experimental characterizations combined with first-principles studies reveal that the tetragonal phase is gradually introduced into the cubic phase as the Si content increases, hence modifies the Fe-Fe interatomic distance. The reduction of the overall Fe-Fe magnetic exchange interactions contributes to the broadness of NTE operation-temperature window for LaFe(13-x)Si(x).

Cryogenic abnormal thermal expansion properties of carbon-doped La(Fe,Si)13 compounds.

Recently, La(Fe,Si)13-based compounds have attracted much attention due to their isotropic and tunable abnormal thermal expansion (ATE) properties as well as bright prospects for practical applications. In this research, we have prepared cubic NaZn13-type carbon-doped La(Fe,Si)13 compounds by the arc-melting method, and their ATE and magnetic properties were investigated by means of variable-temperature X-ray diffraction, strain gauge and the physical property measurement system (PPMS). The experimental results indicate that both micro and macro negative thermal expansion (NTE) behaviors gradually weaken with the increase of interstitial carbon atoms. Moreover, the temperature region with the most remarkable NTE properties has been broadened and near zero thermal expansion (NZTE) behavior occurs in the bulk carbon-doped La(Fe,Si)13 compounds.

Zero thermal expansion in NaZn13-type La(Fe,Si)13 compounds.

A zero thermal expansion material in a pure form of NaZn13-type La(Fe,Si)13 was fabricated. Through optimizing the chemical composition, an isotropic zero thermal expansion material is achieved. The obtained materials exhibit a low expansion of |α| < 1.0 × 10(-6) K(-1) (α is the coefficient of linear thermal expansion) over a broad temperature range (15-150 K). The present study indicates that the thermal expansion behavior of the NaZn13-type La(Fe,Si)13 compounds depends mainly on the content of Si element. This new material is desirable in many fields of industry as a reliable and low-cost zero thermal expansion material.

Abnormal thermal expansion properties of cubic NaZn13-type La(Fe,Al)13 compounds.

The cubic NaZn13-type La(Fe,Al)13 compounds were synthesized, and their linear thermal expansion properties were investigated in the temperature range of 4.2-300 K. It was found that these compounds exhibit abnormal thermal expansion behavior, i.e., pronounced negative thermal expansion (NTE) or zero thermal expansion (ZTE) behavior, below the Curie temperature due to the magnetovolume effect (MVE). Moreover, in the La(Fe,Al)13 compounds, the modification of the coefficient of thermal expansion (CTE) as well as the abnormal thermal expansion (ATE) temperature-window is achieved through optimizing the proportion of Fe and Al. Typically, the average CTE of the LaFe13-xAlx compounds with x = 1.8 reaches as large as -10.47 × 10(-6) K(-1) between 100 and 225 K (ΔT = 125 K). Also, the ZTE temperature-window of the LaFe13-xAlx compounds with x = 2.5 and x = 2.7 could be broadened to 245 K (from 5 to 250 K). Besides, the magnetic properties of these compounds were measured and correlated with the abnormal thermal expansion behavior. The present results highlight the potential application of such La(Fe,Al)13 compounds with abnormal thermal expansion properties in cryogenic engineering.

Enhanced negative thermal expansion in La(1-x)Pr(x)Fe10.7Co0.8Si1.5 compounds by doping the magnetic rare-earth element praseodymium.

Experiments have been performed to enhance negative thermal expansion (NTE) in the La(Fe,Co,Si)13-based compounds by optimizing the chemical composition, i.e., proper substitution of La by magnetic element Pr. It is found that increasing the absolute value of the average coefficient of thermal expansion (CTE) in the NTE temperature region (200-300 K) attributes to enhancement of the spontaneous magnetization and its growth rate with increasing Pr content. Typically, the average CTE of La(1-x)Pr(x)Fe10.7Co0.8Si1.5 with x = 0.5 reaches as large as -38.5 × 10(-6) K(-1) between 200 and 300 K (ΔT = 100 K), which is 18.5% larger than that of x = 0. The present results highlight the potential applications of La(Fe,Co,Si)13-based compounds with a larger NTE coefficient.

Optimization of thermoelectric efficiency in SnTe: the case for the light band.

p-Type PbTe is an outstanding high temperature thermoelectric material with zT of 2 at high temperatures due to its complex band structure which leads to high valley degeneracy. Lead-free SnTe has a similar electronic band structure, which suggests that it may also be a good thermoelectric material. However, stoichiometric SnTe is a strongly p-type semiconductor with a carrier concentration of about 1 × 10(20) cm(-3), which corresponds to a minimum Seebeck coefficient and zT. While in the case of p-PbTe (and n-type La3Te4) one would normally achieve higher zT by using high carrier density in order to populate the secondary band with higher valley degeneracy, SnTe behaves differently. It has a very light, upper valence band which is shown in this work to provide higher zT than doping towards the heavier second band. Therefore, decreasing the hole concentration to maximize the performance of the light band results in higher zT than doping into the high degeneracy heavy band. Here we tune the electrical transport properties of SnTe by decreasing the carrier concentration with iodine doping, and increasing the carrier concentration with Gd doping or by making the samples Te deficient. A peak zT value of 0.6 at 700 K was obtained for SnTe0.985I0.015 which optimizes the light, upper valence band, which is about 50% higher than the other peak zT value of 0.4 for GdzSn1-zTe and SnTe1+y which utilize the high valley degeneracy secondary valence band.

Scalable Photochromic Film for Solar Heat and Daylight Management.

The adaptive control of sunlight through photochromic smart windows could have a huge impact on the energy efficiency and daylight comfort in buildings. However, the fabrication of inorganic nanoparticle and polymer composite photochromic films with a high contrast ratio and high transparency/low haze remains a challenge. Here, a solution method is presented for the in situ growth of copper-doped tungsten trioxide nanoparticles in polymethyl methacrylate, which allows a low-cost preparation of photochromic films with a high luminous transparency (luminous transmittance Tlum = 91%) and scalability (30 × 350 cm2 ). High modulation of visible light (ΔTlum = 73%) and solar heat (modulation of solar transmittance ΔTsol = 73%, modulation of solar heat gain coefficient ΔSHGC = 0.5) of the film improves the indoor daylight comfort and energy efficiency. Simulation results show that low-e windows with the photochromic film applied can greatly enhance the energy efficiency and daylight comfort. This photochromic film presents an attractive strategy for achieving more energy-efficient buildings and carbon neutrality to combat global climate change.

Giant negative thermal expansion in NaZn13-type La(Fe, Si, Co)13 compounds.

La(Fe, Si)13-based compounds are well-known magnetocaloric materials, which show a pronounced negative thermal expansion (NTE) around the Curie temperature but have not been considered as NTE materials for industrial applications. The NaZn13-type LaFe13-xSix and LaFe11.5-xCoxSi1.5 compounds were synthesized, and their linear NTE properties were investigated. By optimizing the chemical composition, the sharp volume change in La(Fe, Si)13-based compounds was successfully modified into continuous expansion. By increasing the amount of Co dopant in LaFe11.5-xCoxSi1.5, the NTE shifts toward a higher temperature region, and also the NTE operation-temperature window becomes broader. Typically, the linear NTE coefficient identified in the LaFe10.5Co1.0Si1.5 compound reaches as much as -26.1 × 10(-6) K(-1), with an operation-temperature window of 110 K from 240 to 350 K, which includes room temperature. Such control of the specific composition and the NTE properties of La(Fe, Si)13-based compounds suggests their potential application as NTE materials.

Self-Stacked 3D Anisotropic BNNS Network Guided by Para-Aramid Nanofibers for Highly Thermal Conductive Dielectric Nanocomposites.

The enhancement of the heat-dissipation property of polymer-based composites is of great practical interest in modern electronics. Recently, the construction of a three-dimensional (3D) thermal pathway network structure for composites has become an attractive way. However, for most reported high thermal conductive composites, excellent properties are achieved at a high filler loading and the building of a 3D network structure usually requires complex steps, which greatly restrict the large-scale preparation and application of high thermal conductive polymer-based materials. Herein, utilizing the framework-forming characteristic of polymerization-induced para-aramid nanofibers (PANF) and the high thermal conductivity of hexagonal boron nitride nanosheets (BNNS), a 3D-laminated PANF-supported BNNS aerogel was successfully prepared via a simple vacuum-assisted self-stacking method, which could be used as a thermal conductive skeleton for epoxy resin (EP). The obtained PANF-BNNS/EP nanocomposite exhibits a high thermal conductivity of 3.66 W m-1 K-1 at only 13.2 vol % BNNS loading. The effectiveness of the heat conduction path was proved by finite element analysis. The PANF-BNNS/EP nanocomposite shows outstanding practical thermal management capability, excellent thermal stability, low dielectric constant, and dielectric loss, making it a reliable material for electronic packaging applications. This work also offers a potential and promotable strategy for the easy manufacture of 3D anisotropic high-efficiency thermal conductive network structures.

In vitro degradation behavior of silica nanoparticles under physiological conditions.

Understanding the degradability of silica nanoparticles is significant for the rational design of desired nanomaterials for various biomedical applications. However, the effect of the intrinsic properties of silica nanoparticles, such as particle shape, surface chemistry, and porosity, on kinetic degradation process under different extrinsic conditions has still received little attention. Herein, mesoporous silica nanoparticles (MSNs) with different aspect ratios (ARs, 1, 2, and 4), the corresponding PEG-functionalized MSNs, and amorphous Stöber spherical silica nanoparticles were specially designed and their degradation was evaluated in in vitro simulated physiological media. The results show that shape, surface properties and porosity of nanoparticles, as well as the component of simulated physiological media, play important roles in tuning the degradation kinetics and behaviors. Sphere-shaped MSNs have a faster degradation rate than rod-shaped counterparts. Naked MSNs are eroded from particle external surface, while PEGylated MSNs from interior of particles. And spherical MSNs display more extensive degradation than amorphous silica nanoparticles. The presence of fetal bovine serum (FBS) in Dulbecco's Modified Eagle's Medium (DMEM) can accelerate the degradation process. These results can provide useful guidelines for the rational design of silica nanoparticles for biomedical applications.

Overcoming multidrug resistance with mesoporous silica nanorods as nanocarrier of doxorubicin.

Multidrug resistance (MDR) is a major obstacle to the effective chemotherapy in many human malignancies. Nanoparticulate drug delivery systems (NDDSs) have been reported to be able to bypass MDR, but the cancer therapeutic efficacy is still limited. In this study, we firstly designed the nonspherical mesoporous silica nanorods (MSNRs) with aspect ratio (AR) of 1.5 and 5 as drug delivery systems of doxorubicin to overcome multidrug resistance. For drug loading, the long-rod MSNRs (NLR, AR = 5) showed higher drug loading capacity of doxorubicin (DOX) than the short-rod MSNRs (NSR, AR = 1.5). NLR encapsulated DOX had increased intracellular DOX accumulation in drug-resistant Chinese hamster ovary (CHO) cells compared with free DOX by observablly increased cellular uptake and significantly prolonged intracellular drug retention. It further exhibited increased cytotoxicity compared with free DOX under different drug concentrations. These findings may provide a new perspective for designing high-performance nanoparticulate drug delivery systems for bypassing multidrug resistance of cancer therapy.