Metallic Phase Research Articles

The cation exchange driving multi-phase regulation in Co7Fe3/Co@NC for enhanced broadband electromagnetic wave absorption

Phase engineering offers distinctive advantages in designing efficient electromagnetic wave (EMW) absorbers. The manipulation of the interaction and arrangement of different multi-phase systems enables the achievement of more precise EMW absorption. However, the transition mechanism from single metal phases to metal/alloy phases has not yet been fully revealed. Here, we employ multiphase engineering driven by cation exchange reactions to finely control the proportion of Co/Co7Fe3 phases and regulate electromagnetic parameters. The introduction of cavities and heteroatoms through cation exchange enables optimized defect distribution and composition, which enhances both impedance matching and electromagnetic attenuation capabilities. Specifically, we yield hollow Co7Fe3/Co@N-doped carbon (H-Co7Fe3/Co@NC) embedded in high-crystallinity graphite carbon after high-temperature pyrolysis, which promotes significant electron transfer between phases, thus enhancing conduction and polarization losses. H-Co7Fe3/Co@NC exhibits ultra-strong reflection loss (RL) of −59.70 dB at 9.37 GHz and achieves broadband absorption of 6.01 GHz at 2.1 mm. This study highlights the influence of Co7Fe3/Co heterogeneous structures on absorption performance and validates the electromagnetic response mechanism of multi-phase heterostructures through COMSOL finite element simulation analysis. Thus, this work paves the way for applying multi-phase engineering driven by cation exchange reactions for advanced absorbers.

The Effect of Adding the Mishraq Sulfur Ore on the Physical and Chemical Properties of Al-Angor and Al-Nahrawan Clays to Producing Lightweight Bricks

This paper aims to examine the possibility of producing lightweight laboratory clay Bricks by adding sulfur ore powder in different weight ratios ranging from 0, 10, 20, 30, 40, to 50% as supplementary materials to two types of clays taken from two different sites, which is the Al-Angor clay region near the city of Ramadi and the Al-Nahrawan clay region. The bricks burned at temperatures of 950 and 1050 C°٬ and the longitudinal Shrinkage tests, bulk density, water absorption, compression strength, and efflorescence were measured. The X-ray diffraction analysis was executed to determine the formed metal phases. The results of the tests showed a direct proportion between longitudinal contraction and water absorption ratio with the addition of sulfur ore and high burning temperature. While bulk density and compression strength are inversely proportional to the sulfur ratio and high burning temperature. Efflorescence tests showed a decrease in the efflorescence rate with an increase in the proportion of sulfur ore.

Revealing the role of 1T- & 2H- molybdenum Disulfide/Nickel sulfide heterojunction for efficient overall water splitting

In the ongoing quest for cost-effective and durable electrocatalysts for hydrogen production—a critical element of sustainable energy transformation—the 1T phase of Molybdenum Disulfide (MoS2) faces challenges due to its thermodynamic instability and the trade-off between efficiency and durability. Conversely, the 2H phase of MoS2, often disregarded in favor of the metallic 1T phase, suffers from its inert nature and limited active sites. To overcome these limitations, this study employs a straightforward hydrothermal synthesis strategy that couples both 1T and 2H phases of MoS2 with Ni3S2, forming 1T- and 2H- MoS2/Ni3S2 heterojunctions. Enhanced by Ni3S2′s abundant active sites, improved electron transport capabilities, synergistic interface effects, and better structural stability, these heterojunctions achieve a high current density exceeding 500 mA cm−2 at low overpotentials, along with prolonged durability for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolytes. Remarkably, an electrolyzer assembly utilizing 1T-MoS2/Ni3S2 as the cathode and 2H-MoS2/Ni3S2 as the anode demonstrates a competitive voltage of 1.58 V at 20 mA cm−2, showcasing superior performance in overall water splitting compared to other non-noble metal-based electrocatalysts. This study not only offers a viable method for synthesizing efficient and stable electrocatalysts for water splitting using transition metal-based heterogeneous structures but also addresses the fundamental challenges associated with 1T and 2H phases of MoS2.

Attaining high-rate hydrogen evolution via SILAR deposited bimetallic nickel cobalt boride electrode: Exploring the influence of Ni to Co ratio

For the first time, a bimetallic Nickel Cobalt Boride (NCB) film with varying Ni to Co ratios was synthesized on stainless steel via the SILAR method. The NCB2 film (1:1 ratio) exhibited a mixed phase of metal boride and oxy-hydroxide with a highly porous, flaky-type morphology, while NCB1 (1:3 ratio) and NCB3 (3:1 ratio) showed only oxidized metal phases and agglomerated clusters. EDX confirmed the purity of the samples, and XPS indicated higher oxidation in NCB1 and NCB3 compared to NCB2. For HER, NCB2 showed the lowest overpotential (80 mV) compared to NCB1 (96 mV) and NCB3 (101 mV), and the smallest Tafel slope value (71 mV/dec). HER kinetics followed a Volmer-Heyrovsky mixed reaction path. NCB2 exhibited the highest Cdl value (16.55 mF/cm2) and the largest electrochemical active surface area (413.7 cm2), outperforming NCB1 (333.125 cm2) and NCB3 (205 cm2). At an overpotential of 100 mV, NCB2's TOF value was 8.23 s⁻1, higher than NCB1 (1.4 s⁻1) and NCB3 (1 s⁻1). For OER, NCB2 showed the highest Cdl value (106 mF/cm2) and ECSA value (2650 cm2). The Faradic efficiency of NCB2 was ∼98% after 190 h. Hydrogen evolution rates for NCB1, NCB2, and NCB3 as cathodes were 952 mL/h, 1022 mL/h, and 800.8 mL/h, respectively. In a prototype electrolyzer, NCB2 enhanced the hydrogen evolution rate by 30% in bifunctional mode to 1334.6 mL/h. After 100 h, performance declined by only 2.7% due to surface oxidation and phase changes. This achievement marks a milestone towards low-cost green hydrogen production, achieving the highest rate of hydrogen evolution as ever reported.

Giant Photodegradation Rate Enabled by Vertically Grown 1T/2H MoS2 Catalyst on Top of Silver Nanoparticles

The exaltation of the photodegradation performance of dichalcogenide MoS2 grown on top of silver nanoparticles (Ag‐NPs) is reported on. The fabricated MoS2 nanosheets nucleate vertically from Ag‐NPs seeds, enabling the growth of both metallic and semiconductor phases 1T/2H‐MoS2. Findings reveal remarkable enhancement of the Raman scattering and an exceptional broadband optical absorption attributed to plasmonic effects induced by the presence of both metallic 1T‐MoS2 and Ag‐NPS at 2H‐MoS2 interfaces. To leverage this effect, photodegradation tests are conducted to remove methyl orange pollutant. Notably, results reveal a significant increase in photodegradation efficiency and rate constant, reaching up to 120% and 550% over pristine 2H‐MoS2, respectively. This finding underscores the role of Ag‐NPs and 1T‐MoS2 tandem to unlock the superior photodegradation properties of vertically aligned 2H‐MoS2 toward methyl orange, paving the way for the development of dichalcogenide‐based hybrid photocatalyst for wastewater treatment and environmental remediation.

Prediction of simultaneous enhancement of Goos-Hänchen shift and reflectance in VO2 grating structure

Vanadium dioxide (VO2) material stands out in the family of the phase change materials due to its temperature-dependent phase transition properties, which make it a promising candidate for the temperature-dependent optoelectronic devices. Enhancement of the Goos-Hänchen (GH) shift is essential in VO2-based nanostructures for their applications, but it has been limited to the multilayered structures with VO2 materials so far. Here, we theoretically investigate the GH shift and corresponding reflectance in the VO2-based grating structure. We evidence that this structure has two GH peaks (3107λ and 2266λ) and high reflectance values (both up to 1) when VO2 is in the insulating phase as well as the maximum GH valley (−1061λ) and low reflectance (0.19) when VO2 is in the metallic phase. The electromagnetic field distributions in this hybrid structure suggest that the guided mode resonances (GMRs) can be excited no matter whether VO2 is in its insulating or metallic phases due to the couplings between the incident waves and the adjacent evanescent diffracted order waves, which produces their enhanced GH shifts. Different from the former case with the high reflectances and the large GH shifts, the latter has the low maximum magnetic field intensity due to the lossy property of the metallic VO2, which leads to the low reflectance and small GH valley value. Additionally, we have also found that by the alterations of the temperature-dependent conductivity of VO2 and the geometric parameters of the structure allows for the control the magnitude and position of the GH peak or valley. The simultaneously enhanced GH shifts and reflectances in the VO2-based grating structure, associated with its controllable features, enable it an effective configuration for establishing the temperature sensors and optoelectronic switches.

Cutting performance and wear mechanism of submicron and ultrafine Ti(C, N)-based cermets

The complex thermal-mechanical coupling among Ti(C, N)-based cermet tool, workpiece and chip affects immensely the tool life, machining quality and costs during high-speed cutting, which makes the investigation on wear mechanisms of tools quite important. In this work, submicron and ultrafine Ti(C, N)-based cermet tools were prepared by vacuum sintering technology, and the cutting performance of the tools was evaluated by continuous dry cutting. The aim of this work is to unravel the wear mechanisms of submicron and ultrafine Ti(C, N)-based cermet tools based on the cutting performance and wear characteristics of both the cutting tools and chips generated during high-speed cutting. The Vickers hardness, flexural strength and tool lifespan of ultrafine Ti(C, N)-based cermets are significantly superior to those of submicron Ti(C, N)-based cermets because of grain refinement strengthening and the improved distribution of metal phases. Tool wear depends to a large extent upon the contact states and heat transfer ability at different locations of the tool edge, which are characterized by simultaneous action and mutual transition from abrasive, adhesion, surface fatigue and oxidative wear. Overall, ultrafine Ti(C, N)-based cermet tools with excellent comprehensive properties exhibit a distinctly reduced tool wear at different wear regions.

New correlations for focusing effect evaluation of the light metal layer in the lower head of a nuclear reactor in case of severe accident

In case of a severe accident (SA) in a nuclear reactor, the core heats up and materials melt and relocate to the lower head of the vessel. In such configuration, stratification occurs between the oxide and metal phases present in the melt. When the metal phase is lighter than the oxide phase, the maximum heat flux applied to the vessel wall is concentrated at the location of this top metal layer, creating the so-called “focusing effect”. The modelling of the focusing effect is essential for SA codes to properly evaluate the vessel failure time or to demonstrate the vessel integrity, when In Vessel Retention (IVR) strategy is implemented. However, existing correlations used in SA codes for focusing effect modelling have some limitations: if the thickness of the metal layer becomes very small, they predict an extremely high heat flux. Moreover, they were validated with tests using water, whereas the Prandtl number was found to play a significant role in this heat transfer.In this paper, the focusing effect is studied based on 3D Direct Numerical Simulations (DNS) of a cylindrical metal layer, covering all possible metal layer characteristics in terms of geometry and boundary conditions, especially for its top surface where the intensity of radiative heat transfer may vary. The analysis of the fluid behavior and the quantitative results obtained allow to derive new correlations and a new model based on the radial profile of the mean temperature of the system and on the radial profile at the top surface. Results at reactor scale confirm the overestimation of existing 0D model used in SA codes for a thin metal layer and highlight the relevance of the proposed model for focusing effect evaluation during transient situations.

Effect of partition arrangement of metal hydrides and phase change materials on hydrogen absorption performance in the metal hydride reactor

Metal hydride (MH) suffers from strong thermal effects during hydrogen absorption. To fully utilize the reaction heat during hydrogen absorption, phase change material (PCM) can be used to achieve efficient thermal management in the reactor. A novel MH-PCM reactor with the partition arrangement of MH and PCM was proposed in this paper. Then, the two-dimensional multiphysics coupled model of the reactor was developed, and the effects of the number of partitions n, the mass of PCM and the hydrogen absorption pressure Pa on the hydrogen absorption performance were discussed detailedly. The results indicated that the novel MH-PCM reactor not only increases the heat transfer area and boots the hydrogen absorption rate, but also improves the uniformity of temperature distribution. As the n increases from 2 to 5, the hydrogen absorption time gradually shortens. Compared to the conventional MH-PCM reactor, the time for 90% hydrogen absorption shortens by 67.13%. Furthermore, the hydrogen absorption rate can be enhanced with the increasing mass of PCM and Pa. However, the larger these values are, the weaker the enhancement effect becomes. The results of this paper may provide a new direction for the optimized design and engineering application of MH-PCM reactors.

Tailoring the Hydrogen Spillover Effect in Ni-Based Heterostructure Catalysts for Boosting the Alkaline Hydrogen Oxidation Reaction.

Improving the catalytic efficiency of platinum group metal-free (PGM-free) catalysts for the sluggish alkaline hydrogen oxidation reaction (HOR) is crucial to the anion exchange membrane fuel cell. Recently, numerous Ni-based heterostructures have been designed based on bifunctional theory to enhance HOR activity by optimizing the binding energy of both H* and OH*; however, their activities are still far inferior to those of PGM catalysts. Indeed, the long transfer pathway for intermediates between different active sites in such heterostructures has rarely been investigated, which could be the reason for the bottleneck. Here, we design a Ni/MoOxHy heterostructure catalyst to promote H* migration from the Ni side to the interface for alkaline HOR via the hydrogen spillover effect. In situ X-ray absorption fine structure, Raman characterizations, H/D kinetic isotope effects, and theoretical calculations have proven facile H* migration from the Ni side to the interface, which further reacts with OH* on the MoOxHy surface. Besides, the hydrogen spillover effect is also beneficial for the preservation of the metallic phase of Ni during the reaction. The catalyst exhibits a high activity with Jk,m of 58.5 mA mgNi-1 and j0,s of 42 μA cmNi-2, which is among the best PGM-free catalysts and is even comparable to some PGM catalysts. It also shows the highest power density (511 mW cm-2) as a PGM-free anode when assembled into fuel cells under moderate back pressure. These findings prove that in addition to optimizing electrophilicity and oxophilicity for active sites, we could also improve the HOR activity from the transfer pathway for intermediates, which provides insight into the design of other efficient HOR catalysts.

Ground-state phase diagram of the unconventional Hubbard chain with bond–charge interaction

Using the field-theory approach combining bosonization and renormalization group, we investigate the weak-coupling phase diagram of the unconventional Hubbard chain, where in addition to a bond–charge interaction (X), the Hubbard interaction differs between odd (Uo) and even (Ue) sites. The result shows that at quarter filling, the unequal Hubbard repulsion has a great influence on low-energy charge excitations. For the attractive X, the umklapp scattering always exists, and the ground state only exhibits a spin-gapless insulating phase with dominant spin-density-wave correlations. For the repulsive X, the umklapp processes only take place if both Uo and Ue are greater than 8Xcos(π/4), and the phase diagram consists of three phases, a metallic phase with the spin-gapped singlet superconducting correlation, and two insulating phases characterized by the spin-density-wave and charge-density-wave correlations. We also present the phase diagram of the standard t-U-X chain in the case of non-half filling.

Hydrogen technologies for decarbonization of ferrous metallurgy: scientific background and technical capabilities

To date, the use of ferrous hydrogen in metallurgy is considered from several positions. First, the partial or complete replacement of carbon with hydrogen reduces greenhouse gas emissions of CO2. Secondly, due to the different chemical affinity for oxygen, it becomes possible to selectively (selectively) extract components from complex complex ores and man-made materials. Thirdly, the absence of carbon in the reaction zone will make it possible to obtain a metal with a low content of carbides, which in many cases increases the demand for the product. Thermodynamic calculations of a multicomponent oxide system (Ni, Fe, P, Zn, Mn, V, Cr, O) in the presence of various reducing agents: carbon, hydrogen are performed using the TERRA software package, and their combined effects are considered. It is shown that the type of reducing agent affects the temperature of the beginning of the reduction of metals and the degree of their metallization. Thus, by selecting the type of reducing agent, its quantity, and the temperature of the process, it is possible to selectively extract some metals, and leave others in an oxidized state. Ilmenite concentrate in the form of a briquette was used in laboratory tests. The analysis of the iron reduction process using carbon or hydrogen as a reducing agent has been carried out. In comparison with the results obtained using carbon, the kinetics of iron reduction with hydrogen is higher. At the same time, the reduction proceeds with the formation of metallic iron, rutile (TiO2) and residual ilmenite. Whereas, in a carbothermic process occurring at higher temperatures (1000–1300 ℃), the reduction products are iron and iron ditanate (FeTi2O5). In addition, an important advantage of selective reduction by gas is the possibility of subsequent separation of the metallic and oxide phases by melting, without fear of secondary reduction due to solid carbon residues.

Exploring photocatalytic tetracycline removal performance under simulated sunlight irradiation: Milling time effect on metallic reduction of MnO/ZrO2 mixed oxide

In the present research, it is reported that ball milling technique can be applied to enhance the photocatalytic properties of MnO and ZrO2 metal oxide powders (MZOx) furthermore the fabricated photocatalyst can be used for the degradation of tetracycline (TTC). XRD analyses revealed that increasing the milling time resulted in the formation of a pure metallic Mn crystal phase, which boosted the antibiotic degradation rate. It was confirmed by SEM technique that the morphological structures of the particles were generally small and uniform. The band gap energy was calculated as 3.70 eV for the hybrid metal oxide. Additionally, the adsorptive and photoluminescence features were illuminated via DRS and PL analyses. The effect of milling time had a major impact on the photodegradation rate of TTC, and the 8 h milling sample (MZOx-8h) exhibited the highest catalytic degradation activity (79.4 %). Low photocatalytic activity was obtained at acidic pHs and increased at alkaline pHs. The presence of H2O2 sharply decreased photocatalytic process time (60 min) and 94.3 % of the TTC was degraded at 7.5 mM H2O2. The photocatalytic degradation process proceeded through superoxide radicals and was supported by holes. The stability of MZOx-8h almost remained constant (70.02 %) even after seven cycles. It was determined that the presence of oxalic acid positively affected the progress of TTC degradation reactions. Further, practical application areas were investigated and MZOx-8h doped on support materials was found to be suitable for such applications in proportion to the doping ratio. Finally, it was demonstrated that MZOx-8h exhibited remarkable performance in photocatalytic reactions of different types of organic pollutants. The synergistic nature of MnO and ZrO2 with the contribution of ball milling time effect resulted in high photocatalytic activity.

Magnetic ferroelectric metal in bilayer Fe3GeTe2 under interlayer sliding

The inherent interlayer freedom in van der Waals stacked materials provides an excellent opportunity to investigate ferroelectric-like behavior through interlayer translation. Based on first-principles calculations, we find that the interlayer sliding in Fe3GeTe2 (FGT) bilayer enables the coexistence of polarization, metallicity, and ferromagnetism. We find that the polarization is induced by the uncompensated vertical interlayer charge transfer, and can be switched by an in-plane interlayer sliding. A moderate biaxial strain can reverse the polarization direction of the sliding FGT bilayer. The vertical polarization disentangles with the in-plane conductivity as was previously seen in the sliding ferroelectric WTe2 bilayer. Our work proposes an extremely rare magnetic ferroelectric metal phase that is useful for magnetoelectric and spintronic applications.

Direct conversion of biogas to syngas over bimetallic nickel–cobalt supported on α-alumina catalysts

Syngas is an essential feedstock for many valuable chemicals, produced primarily by steam reformation of methane. Recently, dry reformation (reaction between methane and carbon dioxide) has gained importance as both the reactants are greenhouse gases (GHGs). However, dry reformation (DRM) produces syngas with a low H2/CO (<1.0). The DRM requires catalyst such as nickel supported on alumina, which results in higher coke. In this study, 6Ni–6Co/α-Al2O3 and 12Ni/α-Al2O3 catalysts were prepared by wetness impregnation. The catalysts were characterized using FESEM, XRD, XPS, BET, H2-TPR, NH3-TPD and H2-Chemisorption. The catalyst performance under DRM conditions were carried out in a fixed bed reactor at 20,000 ml/gcat.hr GHSV, between 600 °C and 700 °C, at atmospheric pressure. The performance of the catalysts was compared based on conversion of methane and carbon dioxide, hydrogen to carbon monoxide and coke deposition. The rates of consumption of methane carbon dioxide were found to be equal, and higher rates were observed for 6Ni–6Co/α-Al2O3, which is attributed to NiAl2O4/CoAl2O4 phase of active metals, higher surface area, smaller crystallite size and higher dispersion. This active phase of catalyst also responsible for higher rate of CO2 adsorption and reduced coke deposition. Highest H2/CO was found to be 1.26 for 6Ni–6Co/α-Al2O3.

Chemical Imaging of Carbide Formation and Its Effect on Alcohol Selectivity in Fischer Tropsch Synthesis on Mn-Doped Co/TiO2 Pellets.

X-ray diffraction/scattering computed tomography (XRS-CT) was used to create two-dimensional images, with 20 μm resolution, of passivated Co/TiO2/Mn Fischer-Tropsch catalyst extrudates postreaction after 300 h on stream under industrially relevant conditions. This combination of scattering techniques provided insights into both the spatial variation of the different cobalt phases and the influence that increasing Mn loading has on this. It also demonstrated the presence of a wax coating throughout the extrudate and its capacity to preserve the Co/Mn species in their state in the reactor. Correlating these findings with catalytic performance highlights the crucial phases and active sites within Fischer-Tropsch catalysts required for understanding the tunability of the product distribution between saturated hydrocarbons or oxygenate and olefin products. In particular, a Mn loading of 3 wt % led to an optimum equilibrium between the amount of hexagonal close-packed Co and Co2C phases resulting in maximum oxygenate selectivity. XRS-CT revealed Co2C to be located on the extrudates' periphery, while metallic Co phases were more prevalent toward the center, possibly due to a lower [CO] ratio there. Reduction at 450 °C of a 10 wt % Mn sample resulted in MnTiO3 formation, which inhibited carbide formation and alcohol selectivity. It is suggested that small MnO particles promote Co carburization by decreasing the CO dissociation barrier, and the Co2C phase promotes CO nondissociative adsorption leading to increased oxygenate selectivity. This study highlights the influence of Mn on the catalyst structure and function and the importance of studying catalysts under industrially relevant reaction times.

FCC twins and martensites responses of metastable dual-phase high entropy alloy to friction stir processing

Fe50Mn30Co10Cr10 dual-phase high entropy alloy (DP-HEA) has good application prospects in the nuclear and automotive industries due to its strength-ductility synergistic effect. The initial volume fractions of FCC twins and HCP martensites in Fe50Mn30Co10Cr10 HEA affect the relative contribution of transformation-induced plasticity and twinning-induced plasticity to the alloy's strength and ductility under loading conditions. Understanding the relationship between FCC twins and martensites is crucial during the friction stir process (FSP). In this study, the microstructure of Fe50Mn30Co10Cr10 HEA as FSP condition was studied. The HCP phase in the base metal almost completely transformed into the FCC phase during FSP. Both FCC twin and HCP martensite transformations serve to alleviate strain in the FCC matrix. The initiation of FCC twin and martensite formation depends on critical stress levels at different temperatures. Higher strain and coarser grains promote more martensite formation, while finer grains and lower strain impede it, causing FCC twins to occur before HCP martensites during the cooling process of materials in the processed zone. These findings offer insights into controlling the volume fractions of twins and martensites in FSPed DP-HEA, thereby potentially enhancing the mechanical properties of DP-HEA.

Hardness and Microstructure Characterization of Hardfacing Alloys Deposited by The Shielded Metal Arc Welding (SMAW) on AISI 1045 Medium Carbon Steel

A ring frame is a machine used for yarn production in the textile industry. Continuous use of the machine results in wear on the shaft timing pulley on the ring frame machine. To improve this condition, repairs are needed, one of which uses the hardfacing method. This study aims to determine the effect of hardfacing on the microstructure and hardness of the shaft timing pulley made from AISI 1045. The hardfacing process used the shielded metal arc welding (SMAW) method with welding current variations of 115 A, 125 A, 135 A, 145 A, and 155 A. In this study, the electrode used was AWS A5.1 E7018 with a diameter of 3.2 mm. The hardfacing product obtained was then finished with a lathe to produce a shaft with a final diameter of 30 mm. In this study, microstructure and hardness tests were carried out on specimens before and after finishing. The results of this study showed that an increase in current caused an increase in the number of pearlite phases in the weld metal and HAZ (heat-affected zone) areas. While in the base metal, the increase in current increased the number of ferrite phases. The highest hardness value was found in specimens that were hardfaced with a current of 145 A. However, the hardness of the hardfacing layer will decrease with the use of currents greater than 145 A. The hardness of the specimens with hardfacing treatment at a current of 145 A resulted in hardness in the weld metal, HAZ, and base metal of 225 HV, 209 HV, and 203 HV, respectively. After the finishing process, the weld metal, HAZ, and base metal in this specimen produced a hardness of 225 HV, 217 HV, and 208 HV, respectively.

Electro-Thermo-Magnetic Effect-Induced Large Thermoelectric Performance of Calcium Cobaltite Nanocomposites.

As attractive thermoelectric oxides, Ca3Co4O9-based materials have been intensively studied for their applications in recent years. However, their thermoelectric performance is enormously limited due to the contradiction of electrical resistivity and thermal conductivity. Herein, BaFe12O19 nanospheres were introduced into the Ca3Co4O9 matrix. The metallic Ag, ferrites, and matrix phase survived together, and a high density of nanoscale BaFe12O19 precipitation was observed. The reduction of work function could lead to band bending and form an interface potential due to the electro-thermo-magnetic effect contributing to the hole migration. As a result, a huge ZT value of 0.51 for the 8 wt % BaFe12O19/Ca3Co4O9 nanocomposites was obtained at 1073 K, accompanied by a low electrical resistivity of 6.7 mΩ·cm and a high Seebeck coefficient of 217.5 μV/K. In addition, a significant reduction of thermal conductivity (1.11 W/(m·K)) occurred, which was due to the nanoscale ferromagnetic phase effectively scattering the mid- and short-wavelength heat-carrying phonons. The synergistic enhancement of thermoelectric performance confirmed that the electro-thermo-magnetic effect is an effective way to solve the challenging problem of performance deterioration in oxide thermoelectric materials.

Stacking faults along the {111} planes seed pressure-induced phase transformation in single crystal silicon

We explore the onset of phase transformation, at the nanoscale, in single-crystal diamond-cubic silicon (dc-Si) subjected to pressures of 13 GPa using a diamond anvil cell with a methanol-ethanol pressure medium. Transmission electron microscopy reveals two distinct structural features along {111} planes: (1) thin bands of defective dc-Si and (2) thicker bands of body-centered cubic silicon (bc8), surrounded by defective dc-Si. We propose that these features are consistent with shear bands that have been formed by slip along the low energy {111} planes and have a range of thicknesses depending on how much plastic deformation has occurred. The presence of bc8-Si within the thicker bands can be explained by localized regions of high pressure or energy at their center facilitating phase transformation to the metastable metallic β-Sn phase, which in turn, transforms to bc8 on pressure release. Our observations reveal that phase formation in silicon can be shear-activated, the transformation is not nucleation-limited, and its sluggish nature may be due to the slow growth of the metallic phase.