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Pristine Ag2Se has inherent limitations in its Seebeck coefficient and electronic thermal conductivity, necessitating improvements through carrier concentration manipulation. While its porous structure has been utilized to reduce carrier concentrations, achieving optimal values remains challenging. This study explores enhancing Ag2Se with acetylene carbon black (ACB) nanocomposites to further reduce carrier concentrations and improve thermoelectric (TE) properties. ACB, a cost-effective alternative to other carbon materials, has demonstrated potential in enhancing TE performance in various composites. Ag2Se and ACB composites were synthesized by dispersing different ACB weights in a solution, followed by sintering. Characterization using x-ray diffraction (XRD), Transmission and scanning electron microscopy (TEM and SEM), and other techniques confirmed the phase, structure, and morphology of the composites. The addition of ACB resulted in decreased electrical conductivity and increased Seebeck coefficient in Ag2Se, particularly at ACB concentrations up to 5.0 wt%, balancing the power factor (PF). The total thermal conductivity decreased due to mainly reduced electronic thermal conductivity. The 5.0 wt% ACB sample achieved a zT of approximately 0.8 at 383 K, comparable to the performance of composites using more expensive low-dimensional carbon materials.

Geopolymer, an alternative construction material to cement, acquires strength and endurance through the geopolymerization process. However, the study on the early-stage geopolymerization is rare since it occurs rapidly and involves liquid phase, viscous slurry, and gel-like material, making the observation of this process complicated. This research addresses the challenge of observing this process by providing real-time evidence through in situ techniques: Fourier-transformed infrared (FTIR) spectroscopy, X-ray absorption spectroscopy (XAS), and environmental scanning electron microscopy (E-SEM). These methods consistently confirm the formation of aluminosilicate oligomers, short chains of silicate and aluminate species, in the polycondensation Stage I within the initial 5 minutes. This stage involves the reaction of Si-O and Al-O monomers, released during a dissolution process, with available Na2SiO3 from alkaline solutions in the system. In the subsequent polycondensation Stage II, aluminosilicate oligomers polymerize, creating a three-dimensional network of aluminosilicate chains through the crosslinking of Si-O-Si and Si-O-Al bonds. This process continues beyond the initial 5 minutes, gradually nearing completion around 30 minutes, as consistently confirmed by various experimental techniques. Rheological studies on the geopolymer paste flow rate support these interpretations. The study provides compelling direct evidence into the mechanisms of early-stage geopolymerization, significantly contributing to the research field and paving the way for widespread utilization in geopolymer applications.

Silver selenide (Ag2Se) is a promising thermoelectric material for near-room temperature energy conversion. This research developed an innovative approach to enhance the thermoelectric properties of Ag2Se through low-temperature cold sintering process (CSP). Aqua regia, a mixture of hydrochloric and nitric acids, was employed as a liquid medium in CSP, facilitating the localized atomic rearrangement and bonding at intergranular interfaces between Ag2Se particles. This yielded a densely packed sample with merged sub-micron grains and coherent interfaces. Aqua regia-assisted CSP notably improved thermoelectric properties compared to a reference sample without aqua regia. Carrier concentration decreased and carrier mobility increased for the CSP sample with 0.1 M aqua regia, leading to the enhanced electrical conductivity, Seebeck coefficient, and the maximum power factor of 2.13 mWm−1K−2. The addition of aqua regia in CSP consolidation also suppressed phonon thermal conductivity due to sub-micron pores and nanoprecipitates, resulting in low thermal conductivity of 0.5–0.7 Wm−1K−1, and significantly enhanced figure-of-merit (zT) reaching 1.13. Remarkably, the zT of the CSP Ag2Se was very stable against temperatures (±6 % fluctuations), with an average value of 1.06. These findings highlight CSP with aqua regia as an effective route to fabricate high-performance thermoelectric Ag2Se for near-room temperature applications.

Silver selenide (Ag2Se) is a high‐performance thermoelectric (TE) material near room temperature. This research improves its TE figure‐of‐merit (ZT) by varying the sintering temperatures (423–723 K) in the spark plasma sintering (SPS) process with high compression pressure (300 MPa). The SPS compaction of Ag2Se powders synthesized by wet chemical reaction leads to the fast fusion of particles so that the grain boundaries are hardly visible. Furthermore, the fast fusion causes nanopores at the grain surface and some cracks, particularly at higher sintering temperatures. These featured microstructures decrease carrier concentrations and affect the TE properties significantly. The TE measurements show that increasing sintering temperatures results in decreased electrical conductivity and increased magnitude of the Seebeck coefficient due to microstructural defects. Increasing SPS temperatures also suppresses the thermal conductivity from enhancing phonon scattering by defects. The bulk Ag2Se sample sintered at 723 K shows the best TE performance with the maximum ZT of 0.90 with a slight variation from 300 to 400 K. Thus, the high‐temperature SPS with high‐compression pressure is likely to be the key for fabricating bulk Ag2Se with high TE performance.

Lithium-borate-based glass co-doped with nickel and cobalt ions was successfully fabricated by a two-step melt quenching method. The relationship between Ni and Co contents in the glasses was investigated, with a focus on their electrochemical properties and battery performance. Cyclic voltammetry was used to pre-investigate the electrochemical properties of the glass electrodes. It was found that the specific capacitance of all conditions was above 100 F/g. This preliminary study showed that the glass is feasible to use as a Li-ion battery cathode. The Co-rich content sample (NC11) exhibited the highest specific capacity of 380 mAh/g in the first cycle test. However, the specific capacity was dramatically decreased in subsequent cycles due to Li-ion trapping in the glass structure. Additionally, the higher amount of Ni ions in the co-doping Ni/Co-LBO glass enhanced the retention properties. This suggests that Ni-rich content could improve the release of free Li-ions from the host glass structure.

Machine learning (ML) is increasingly being adopted to accelerate the development of materials research. In this work, we applied the ML approach to predict the figure-of-merit (ZT) of thermoelectric (TE) materials. The experimental datasets were gathered from 150 published articles for five high-performance TE groups in the mid-temperature range, i.e., PbTe, Co4Sb12, Mg2Si, BiCuSeO, and Cu2Se, resulting in 1563 data points in total. The chemical formulas of individual compounds, including the dopant types and concentrations, were extracted as ML features using the Magpie software. The ZT value was set as the target value. The model was built based on different regression algorithms, and its accuracy for predicting ZT was evaluated using the coefficient of determination (R2) and the root mean squared error (RMSE). It was found that the model’s accuracy increased with increasing datasets and by incorporating features from experimental parameters (measurement temperature, sintering temperature, and sintering pressure). The final ML model showed relatively high accuracy, with an R2 of 0.859 and an RMSE of 0.156 for a test set. It means that the model can confidently predict the ZT of specific doped compounds in the selected TE groups. To utilize the model effectively, it is implemented as a webpage application with a user-friendly interface so that researchers without ML expertise can explore the ZT values of the doped TE materials. It will certainly be beneficial for experimentalists as a guideline for designing their experiments.

Alkali-activated material is a potential alternative building material. The conventional forming method of alkali-activated is casting. Recently, additive manufacturing technology, or 3D printing, has become increasingly attractive for use in construction due to its advantages in freedom of design, cost-efficiency, and less labor required. However, the proper characteristics of alkali-activated materials for 3D printing are still very limited. In this work, the 3D printing with high calcium fly ash alkali-activated using customized extruder was studied. The variables for the mix proportion were sand-to-fly ash ratio of 1.55, 1.65 and 1.75, and liquid-to-binder ratio of 0.45, 0.50 and 0.55; and printing speed of 140–160 mm/s, interval duration of 10, 20, and 30 min, and nozzle height of for the printing of 10, 11 and 12 mm for the printing. The results showed that for high calcium fly ash activated with sodium hydroxide and sodium silicate, the mix with a sand-to-fly ash ratio of 1.65 and a liquid-to-binder ratio of 0.50 was the most suitable one considering the fast-setting time of 56 min and ease of extruding the mixture with a flowability of 103 %. were the printing speed of 150 mm/s, interval duration between each layer of 3 min, and the nozzle height of 11 mm. The 28-day compressive strength of 23.9 MPa was obtained. The high calcium fly ash was shown to be suitable for 3D printing the presence of calcium reduced setting time and improve the buildability of the 3D printed mortar.

Abstract We investigated the effects of both intrinsic defects and hydrogen atom impurities on the magnetic properties of MgO samples. MgO in its pure defect-free state is known to be a nonmagnetic semiconductor. We employed density-functional theory and the Heyd–Scuseria–Ernzerhof (HSE) density functional. The calculated formation energy and total magnetic moment indicated that uncharged $${\mathrm{V}}_{\mathrm{Mg}}^{0}$$ V Mg 0 and singly charged $${\mathrm{V}}_{\mathrm{Mg}}^{-1}$$ V Mg - 1 magnesium vacancies are more stable than oxygen vacancies (VO) under O-rich growth conditions and introduce a magnetic moment to MgO. The calculated density of states (DOS) results demonstrated that magnetic moments of VMg result from spin polarization of an unpaired electron of the partially occupied valence band, which is dominated by O 2p orbitals. Based on our calculations, VMg is the origin of magnetism and ferromagnetism in MgO. In contrast, the magnetic moment of the magnetic VMg-MgO crystal is suppressed by hydrogen (H) atoms, and unpaired electrons are donated to the unpaired electronic states of VMg when the defect complex Hi-VMg is formed. This suggests that H causes a reduction in magnetization of the ferromagnetic MgO. We then performed experimental studies to verify the DFT predictions by subjecting the MgO sample to a thermal treatment that creates Mg vacancies in the structure and intentionally doping the MgO sample with hydrogen atoms. We found good agreement between the DFT results and the experimental data. Our findings suggest that the ferromagnetism and diamagnetism of MgO can be controlled by heat treatment and hydrogen doping, which may find applications in magnetic sensing and switching under different environmental conditions.

The partial substitution by bismuth (Bi) is aimed to improve magnetic properties of barium hexaferrites from the sol–gel auto-combustion synthesis. The exceptionally high saturation magnetization of 99 emu/g is attributed to the substitution of Fe3+ in tetrahedral 4f1 sites by Bi3+and the highly compact structure without impurity phase. On the other hand, the coercivity is reduced with increasing Bi substitution because the hexagonal particles grow larger and single magnetic domains become multi-domains. Similarly, the co-substitution by bismuth-copper (Bi-Cu) ions substantially enhances the particle size and hence the reduction in coercivity is even more drastic. The reduction in coercivity of barium hexaferrites with high magnetizations are desirable for microwave absorbing and data storage materials. The magnetizations of barium hexaferrites with either Bi or Bi-Cu substitutions follow the law of approach saturation. However, the saturation magnetization is significantly lower by the Bi-Cu substitutions into octahedral 4f2 sites and the presence of the secondary hematite phase.

In this study, we report on the observation of spin current in opposite spin Hall angle materials of polycrystalline bulk-Fe3O4/Co and polycrystalline bulk-Fe3O4/Fe spin Seebeck effect (SSE) devices. In contrast to prior works, a facile and low-cost hot-pressing powder metallurgy process was employed to manufacture the polycrystalline bulk-Fe3O4 samples. The crystal structure, magnetization properties, and electrical resistivity characterizations of the fabricated bulk-Fe3O4, which were performed using x-ray diffraction, vibration sample microscope, and four-point probe, respectively, revealed excellent agreement with those of conventional Fe3O4. By taking advantage of the fact that the SSE signal in our devices is typically contaminated with the anomalous Nernst effect (ANE), we show that the total thermo-voltage obtained from our devices can be enhanced by the significant ANE signals exhibited by the Co and Fe spin detectors. Importantly, the ANE contributions could be filtered out from the main signal by independent measurements of the ANE voltage in SiO2/Co and SiO2/Fe systems, thereby allowing the approximate extraction of the SSE voltage. Our experiments reveal that the polarity of the measured ANE (and pure SSE voltages) are opposite to each other in the bulk-Fe3O4/Co and bulk-Fe3O4/Fe structures, thus proving the opposite spin-hall angles character of these materials. The findings of this work provide a pathway for further exploration of methods through which the thermo-voltage output in future spin-Hall thermopile devices may be improved using materials manufactured via a facile, low-cost, and easily scalable process.

CeO2 nanoparticles were prepared via an ozonolysis assisted co-precipitation method at room temperature (referred to as O3-CeO2) and were calcined at 300 °C for 3 h (referred to as O3-CeO2-300). CeO2 nanoparticles were also prepared by a co-precipitation method with no ozonolysis for comparison (referred to as CeO2-300). The prepared samples were characterized to determine their phase, morphology, functional groups, surface area, valence states and magnetic properties using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry, respectively. The samples exhibited XRD peaks and TEM-selected area electron diffraction corresponding to face centered cubic CeO2, confirming a single phase. The average crystallite sizes were in the range of 8.0 ± 0.3 to 12.0 ± 0.4 nm. TEM imagery revealed a morphological transformation from irregular shapes into hexagonal-like CeO2 when examining O3-CeO2 and O3-CeO2-300 samples, respectively. XPS results showed Ce states in the form of Ce4+ and Ce3+ and oxygen vacancies were observed in all samples. All samples exhibited weak ferromagnetic behavior at room temperature with a maximum magnetization value of 3.6 × 10-3 Am2/kg for O3-CeO2-300. The origin of the ferromagnetism in pure CeO2 is explained on the basis of an F-center exchange mechanism via ferromagnetic Ce3+ (↑↑) coupling.

Activated carbon (AC) from sugarcane bagasse was prepared using dry chemical activation with KOH. It was then subjected to a high-energy ball milling (HEBM) treatment under various milling speeds (600, 1200 and 1800 rpm) to produce AC nanoparticles from micro-size particles. The AC samples after the HEBM treatment exhibited reduced particle sizes, increased mesopore volume and a rich surface oxygen content, which contribute to higher pseudocapacitance. Notably, different HEBM speeds were used to find a good electrochemical performance. As a result, the AC/BM12 material, subjected to HEBM at 1200 rpm for 30 min, exhibited the highest specific capacitance, 257 F g−1, at a current density 0.5 A g−1. This is about 2.4 times higher than that of the AC sample. Moreover, the excellence capacitance retention of this sample was 93.5% after a 3000-cycle test at a current density of 5 A g−1. Remarkably, a coin cell electrode assembly was fabricated using the AC/BM12 material in a 1 M LiPF6 electrolyte. It exhibited a specific capacitance of 110 F g−1 with a high energy density of 27.9 W h kg−1.

Fly ash (FA) and sugarcane bagasse ash (SCBA) are the wastes from lignite power plants and sugar industries, usually disposed of as landfills. In this research, these wastes were effectively utilized as a construction material, namely geopolymer. The effect of the SCBA (0–40 wt.%) addition to the FA geopolymers was investigated. The compressive strength of the FA geopolymers was reduced with the SCBA addition. The reduction was mainly due to the presence of the highly stable and non-reactive quartz (SiO2) phase in SCBA. The SCBA was not dissolved in the alkaline activated solution and hence did not contribute to the geopolymerization process. The unreacted SCBA particles remained in the geopolymer matrix but did not provide strength. However, if the amount of SCBA was about 10 wt.% or less, the impact on the characteristics and properties of FA geopolymers was minimal. Furthermore, this research also studied the dielectric properties of the FA geopolymer/SCBA composites. The relatively large dielectric constant (ε′ = 3.6 × 103) was found for the pristine geopolymer. The addition of SCBA decreased the ε′ slightly due to high carbon content in SCBA. Nevertheless, the variation in ε′ was mainly controlled by the geopolymerization process to form the aluminosilicate gel structure.

Hybrid nanocomposites of bacterial cellulose (BC) and magnetic iron oxide nanoparticles (NPs) are of interest due to their potential for novel applications. Magnetic NPs are typically synthesized by co-precipitation since it is facile, enabling control of their size and distribution. This work investigates the effect of using different starting reactants (Fe(II) and Fe(III) salts) in the fabrication and control of the properties of BC/iron oxide nanocomposites. It was found that the choices of starting reactants are not important for synthesizing NPs outside of the BC networks. However, the starting reactants do affect the formation of NPs when they are synthesized in the BC network. Significant differences in the morphologies, sizes, crystal structures, and magnetic phases of NPs occurs when in this environment. The nanopores of BC networks in some instances force the aggregation of the NPs, either within the pores, or on the surfaces of the fibrils. Nanocomposites synthesized from Fe(II) sulfate and Fe(III) chloride were found to exhibit the highest magnetization. These nanocomposites have potential for flexible sensors, actuators, or electromagnetic shielding. Nanocomposites from Fe(II) acetate and Fe(III) chloride, though exhibiting lower magnetization, preserve a porous structure. Thus, they have potential as adsorbents or for wound healing applications.

Machine learning (ML) has increasingly received interest as a new approach to accelerating development in materials science. It has been applied to thermoelectric materials research for discovering new materials and designing experiments. Generally, the amount of data in thermoelectric materials research, especially experimental data, is very small leading to an undesirable ML model. In this work, the ML model for predicting ZT of the doped BiCuSeO was implemented. The method to improve the model was presented step-by-step. This included normalizing the experimental ZT of the doped BiCuSeO with the pristine BiCuSeO, selecting data for the BiCuSeO doped at Bi-site only, and limiting important features for the model construction. The modified model showed significant improvement, with the R2 of 0.93, compared to the original model (R2 of 0.57). The model was validated and used to predict the ZT of the unknown doped BiCuSeO compounds. The predicted result was logically justified based on the thermoelectric principle. It means that the ML model can guide the experiments to improve the thermoelectric properties of BiCuSeO and can be extended to other materials.

Since the discovery of the spin Seebeck effect (SSE) in 2008, it has become one of the most active topics in the spin caloritronics research field. It opened up a new way to create the spin current by a combination of magnetic fields and heat. The SSE was observed in many kinds of materials including metallic, semiconductor, or insulating magnets, as well as non-magnetic materials. On the other hand, carbon-based materials have become one of the most exciting research areas recently due to its low cost, abundance and some exceptional functionalities. In this work, we have investigated the possibility of the SSE in bulk carbon materials for the first time. Thin platinum film (Pt), coated on the smoothened surface of the bulk carbon, was used as the spin detector via the inverse spin Hall effect (ISHE). The experiment for observing longitudinal SSE in the bulk carbon was set up by applying a magnetic field up to 30 kOe to the sample with the direction perpendicular to the applied temperature gradient. The induced voltage from the SSE was extracted. However, for conductive materials, e.g. carbon, the voltage signal under this set up could be a combination of the SSE and the anomalous Nernst effect (ANE). Therefore, two measurement configurations were carried out, i.e. the in-plane magnetization (IM), and the perpendicular-to-plane magnetization (PM). For the IM configuration, the SSE + ANE signals were detected where as the only ANE signal existed in the PM configuration. The results showed that there were the differences between the voltage signals from the IM and PM configurations implying the possibility of the SSE in the bulk carbon material. Moreover, it was found that the difference in the IM and PM signals was a function of the magnetic field strength, temperature difference, and measurement temperature. Although the magnitude of the possible SSE voltage in this experiment was rather low (less than 0.5 μV at 50 K), this research showed that potential of using low cost and abundant bulk carbon as spin current supplier or thermoelectric power generators. Keywords: Spin Seebeck effect, Anomalous Nernst effect, Inverse spin Hall effect, Bulk carbon

The copper (Cu) substitution in barium hexaferrite (BaFe12O19) crystals from the sol-gel auto-combustion synthesis is demonstrated as a cost-effective pathway to achieve alterable magnetic properties. Subsequent heat treatments at 450 °C and 1050 °C result in irregularly shaped nanoparticles characterized as the M-type BaFe12O19 with the secondary phase of hematite (α-Fe2O3). Despite the mixed phase, the substantial coercivity of 2626 Oe and magnetization as high as 74.8 emu/g are obtained in this undoped ferrite. The copper (Cu) doing strongly affects morphology and magnetic properties of BaFe12−xCuxO19 (x = 0.1, 0.3, and 0.5). The majority of particles become microrods for x = 0.1 and microplates in the case of x = 0.3 and 0.5. The coercivity and magnetization tend to reduce as Cu2+ increasingly substitutes Fe3+. From these findings, magnetic properties for various applications in microwave absorbers, recording media, electrodes, and permanent magnets can be tailored by the partial substitution in hexaferrite crystals.

Nanocrystalline Co2P2O7 and carbon nanofiber (Co2P2O7/CNFs) composites with enhanced electrochemical performance were obtained by calcination after a hydrothermal process with NH4CoPO4∙H2O/bacterial cellulose precursors under an argon atmosphere. SEM images showed that the CNFs were highly dispersed on the surfaces of Co2P2O7 microplates. The diagonal size of the Co2P2O7 plates ranged from 5 to 25 µm with thicknesses on a nanometer scale. Notably, with the optimal calcining temperature, the Co2P2O7/CNFs@600 material has higher specific micropore and mesopore surface areas than other samples, and a maximal specific capacitance of 209.9 F g−1, at a current density of 0.5 A g−1. Interestingly, CNF composite electrodes can enhance electrochemical properties, and contribute to better electrical conductivity and electron transfer. EIS measurements showed that the charge–transfer resistance (Rct) of the CNF composite electrodes decreased with increasing calcination temperature. Furthermore, the Co2P2O7/CNF electrodes exhibited higher energy and power densities than Co2P2O7 electrodes.

Melt-electrospun polycaprolactone (PCL) fibers were fabricated by using NaCl as an additive. The size and morphology of the PCL fibers could be controlled by varying the concentration of the additive. The smallest size of the fibers (2.67 ± 0.57) µm was found in the sample with 8 wt% NaCl, which was an order of magnitude smaller than the PCL fibers without the additive. The melt-electrospun fibers were characterized using the differential scanning calorimeter (DSC), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) techniques. Interestingly, a trace of NaCl was not found in any melt-electrospun fiber. The remaining PCL after melt-electrospinning was evaporated by annealing, and the NaCl residual was found in the glass syringe. The result confirmed that the NaCl additive was not ejected from the glass syringe in the melt-electrospinning process. Instead, the NaCl additive changed the viscosity and the polarization of the molten polymer. Two parameters are crucial in determining the size and morphology of the electrospun fibers. The higher NaCl concentration could lead to higher polarization of the polymer melt and thus a stronger electrostatic force, but it could also result in an exceedingly high viscosity for melt-electrospinning. In addition, the absence of NaCl in the melt-electrospun PCL fibers is advantageous. The fibers need not be cleaned to remove additives and can be directly exploited in applications, such as tissue engineering or wound dressing.

Lead-free (1-x) Ba0.85Ca0.15Ti0.90Zr0.10O3 x Bi0.80Ba0.20FeO3 [(1-x)BCTZ-- xBBF] ceramics, with BBF content (x) between 0 and 0.4, are prepared via the solid-state combustion technique. The effect of BBF content on the phase formation, microstructure, and electric and magnetic properties of BCTZ is studied. From the Rietveld refinement analysis, the BCTZ ceramic shows coexisting orthorhombic and tetragonal phases, with a ratio of 35.4:64.6 and the percentage of the tetragonal phase continuously increases when x increases from 0.02 to 0.1, and becomes purely tetragonal at x ≥ 0.2. When x increases, the average grain size, density, and relative density continuously decrease while the unit cell volume enlarges. The dielectric constant at room temperature (εR) tends to decrease while the dielectric loss at room temperature (tan δR) increases with increased BBF content. For x = 0, a pure BCTZ ceramic, a well-saturated P--E loop is observed with a polarization (Pr) and coercive field (Ec) of 8.94 µC cm-2 and 4.06 kV cm-1, respectively. The ferroelectricity drastically decreases with x=0.02. For x≥ 0.06, the leakage current increases, which suppresses the ferroelectricity. With no BBF content (x=0), the ceramic has diamagnetic properties that change to paramagnetic properties with x=0.02--0.06 and finally to ferromagnetic properties when the BBF increases between 0.10 and 0.40. For x=0.10--0.40, the remnant magnetization (Mr) continuously increases. [ABSTRACT FROM AUTHOR]