Uneven micron-sized pores on the surface of the polycrystalline alumina (Al2O3) substrates can affect their performance as electrical insulating plates. In this study, we investigated the sealing of these pores with amorphous Al2O3 films deposited via atmospheric chemical vapor deposition. Furthermore, we conducted annealing treatments on the samples. The color change of the deposited Al2O3 films was investigated using the Commission Internationale de I’Eclairage color space. Notably, the deposited films initially changed the sample color from white to orange or brown. However, increasing the annealing temperature and duration reversed this discoloration effectively and restored the original white (colorless) appearance of the sample. We measured thermal conductivity using the flame flash method with the H2-O2 flame to assess the influence of sealing. While the unsealed substrate exhibited a thermal conductivity of 4.66 W/mK in the range of 400–500 °C, the annealed and flattened Al2O3 film deposited on the substrate maintained a comparable thermal conductivity of 4.67 W/mK within the same temperature range. This finding demonstrates that our sealing method successfully filled the pores while having minimal influence on thermal conductivity, which is a crucial property for electrical insulation applications.
The structural, microstructural, dielectric, optical, ferroelectric, and magnetic properties of cobalt doped barium calcium titanate (BCT) (Ba0.80Ca0.20Ti1-xCoxO3 with x =0.000, 0.005, 0.010, 0.015, and 0.020) ceramics have been reported in this paper. The ceramic samples were prepared by the conventional solid-state reaction method. For all of the prepared samples, the tetragonal structure with the space group P4mm has been confirmed using the refinement method through rietveld refinement of X-ray diffraction patterns. Field Emission Scanning Electron Microscopy (FESEM) micrographs revealed that the average particle size exists in micrometre range (0.3-0.8) μm. Optical studies revealed a gradual decrease in the energy bandgap from 3.31 eV to 2.71 eV with increasing doping concentration. A decreasing trend was observed in the dielectric characteristics of the material with changing frequencies at room temperature. Ferroelectric (P-E loops) analysis displayed an increase in both remnant polarization and maximum polarization of the ceramic with the increasing applied electric field. The highest value for the energy storage efficiency (η) was calculated to be 20.51%. Magnetic analysis conducted at room temperature revealed the enhancement in ferromagnetism with the increase in doping concentration.
A series of (Mg1-xZnx)3(PO4)2 (x = 0.02-0.10) microwave dielectric ceramics were fabricated by the solid-state reaction method and investigated in terms of crystal structure, chemical bond properties, and dielectric properties were analyzed. The XRD data indicates that (Mg1-xZnx)3(PO4)2 samples belong to the monoclinic crystal with P21/c space group and no detectable secondary phases. The Rietveld refinement was employed to obtain crystal parameters. In addition, the results of chemical bond properties reveal that the lattice energy and ionicity of Mg(2)-O(3) bonds play a primary effect on the dielectric loss and dielectric constant, respectively. The bond energy of Mg(l)-O(2) bonds plays a dominant role in thermal stability. The far-infrared spectroscopy was employed to explore the intrinsic dielectric parameters, and the results showed that peaks below 400 cm-l contributed 78.9% to ε′ and 99.1% to ε″. The Raman data demonstrated that the Raman shift and FWHM exhibit an important influence on Q × f. The optimal performance was achieved in (Mg0.94Zn0.06)3(PO4)2 ceramics: εr = 5.00, Q × f = 84,674 GHz, τf = -59.98 ppm/°C.
Recently, ferroelectric memory utilizing hafnium oxide has emerged as an attractive option compared to existing memory technologies, primarily due to its scalability and energy-efficient advantages. Among them, hafnium zirconium oxide (HZO) is examined for its short-term memory characteristics to achieve a reservoir computing system known to exhibit remarkable polarization properties, being able to switch between distinct polarization states under the influence of an electric field. These unique properties are of utmost importance in ferroelectric memory applications, where they play a pivotal role in the storage and retrieval of binary data. In this study, we identify and experiment with the electrical characteristics of a ferroelectric tunnel junction (FTJ) device with a metal-ferroelectric-semiconductor (MFS) structure using TiN as the top electrode and HZO as the ferroelectric layer. Moreover, we assess the performance of the device by evaluating its maximum 2Pr (remnant polarization) and tunneling electro resistance (TER) values in different conditions of cell area. Furthermore, we analyze and show short-term memory (STM) characteristics and synaptic properties with 5 cycles of potentiation and depression under conditions of stable dynamic range by coordinating identical and incremental pulses. In the case of incremental pulses (> 95%), the MNIST pattern recognition accuracy is higher than in the case of identical pulses (> 94%). Through a sequence of procedures, the synaptic characteristics of FTJs are confirmed to assess their suitability for use as an artificial synaptic device.
Metal oxide-based gas sensors have promising advantages, such as low cost and high sensitivities, but the high working temperature (150°C-300°C) hinders their practical applications. Herein, this study demonstrated a Zinc (Zn)-doped approach to achieve defect-enabled room-temperature acetone gas sensors based on bismuth oxide (Bi2O3) thin film. Through a simple chemical bath deposition method, the varying substitutional doping of zinc (2 wt% to 8 wt%) can induce the morphological transformation of Bi2O3 nanosheets to a cauliflower-like nanostructure, leading to enhanced surface area and active sites. The incorporation of Zn ions can result in oxygen vacancies in the Bi2O3 lattice and the rising of the depletion layer, facilitating the interaction toward acetone molecules at ambient temperatures, leading to an increment of response ∼6. The Zn-doped cauliflower-like Bi2O3 electrode exhibits a superior sensing performance of acetone gas with a low detection limit of 1 ppm and high stability over 90 days. This work underscores the potential of controlled doping of Zn for oxygen vacancy-riched Bi2O3 thin film as a promising room-temperature acetone gas sensor, offering new avenues for the detection of hazardous gases with improved sensitivity.
The significant environmental impact of textile industries, particularly dye pollution from the textile effluents necessitates the urgent attention for its removal. Rhodamine B (RhB), known for its resistance to degradation which poses a considerable challenge. In this study, mesoporous gC3N4-ZnS QDs NCs were synthesized using an ultrasound-assisted co-precipitation method. Comprehensive characterizations, including scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy, photoluminescence spectroscopy, electrochemical impedance spectroscopy, and Brunauer-Emmett-Teller analysis were conducted to evaluate the materials. SEM images revealed a layered structure in the gC3N4 nanosheet, with small crystals clustered together, influencing the electronic and optical properties. The surface of gC3N4 was decorated with ZnS QDs to enhance the catalytic degradation of RhB. TEM analysis confirmed the uniform distribution of ZnS QDs over gC3N4 nanosheet. XRD and XPS analysis results before and after catalysis demonstrated the structural stability of the material. The degradation efficiency was achieved to be 97.8% at a rate constant of 0.077 min-1 within 54 min. The stability and reusability of the NCs were confirmed through six consecutive cycles of catalytic degradation. The present study presents a promising strategy for the degradation of organic pollutants in aquatic ecosystems, offering insights for sustainable mitigation of textile dye pollution.
Thin film thermoelectric technology has immense potential to become a next-generation power source for small-scale electronics. However, the rapid development of thin film thermoelectric still lacks a controllable structural design to improve the performance of thermoelectric devices for required temperature applications. This work presented a controlled thermoelectric design of ZnO-based thin films by Al and Mg co-doping using ALD. Herein, the Mg-doped ZnO sample exhibits the highest Seebeck coefficient of -311.83 μVK-1 at 500oC, while the maximum thermoelectric power factor of 3.68 μWcm-1K-2 is obtained at 300oC, which drops for higher temperatures. This decrease in power factor resulted from the reduction in electrical conductivity above 300oC. Similarly, the Al and Mg co-doped ZnO sample (Mg/Al ≈2 at%) exhibits a high thermoelectric power factor of 3.85 μWcm-1K-2 for ZnO based material due to its moderate electrical conductivity and Seebeck coefficient value at 325oC and behave monotonically for elevated temperatures. Scanning electron microscope (SEM) images show the formation of wedge-shaped structures for Al-incorporated samples, which helps to boost the overall thermoelectric performance. Additionally, we performed XRD, UV-Vis, Hall, and AFM analysis to get a deep insight into structural, optical, electrical, and surface features of the grown thin films and their linkage with the thermoelectric properties.
The mechanical property is one of the most important properties of a material and is determined by the atomic-scale structure. It is thus crucial to establish the theoretical model for the prediction of materials’ mechanical properties, benefiting the material design. In our previous work, we proposed an atomic-scale structure-based model for predicting the Young’s modulus of hydrogenated amorphous carbon; however, the application range of this model is too narrow to be used practically for the materials development. Therefore, in this work, an extended prediction model of Young’s modulus of materials with wide applicability is successfully constructed, based on the two important inherent properties of materials: one is effective coordination number (CNeff) evaluating how densely atoms are structured and the another one is effective bond stiffness (Keff) that is first proposed here and indicates how bonding types contribute the elastic properties. Through the high-throughput molecular dynamics simulations, the predictive model of Young’s modulus (E) is determined as E = 3.37Keff (CNeff - 2.0)1.5. Then we demonstrate that this model is valid for a large variety of materials including both amorphous and crystalline structures, and the accuracy is proven by comparing with other work. Overall, this fundamental work may benefit the preparation, development, and utilization of new materials.
Symmetric solid oxide fuel cells (SSOFCs) are attracting much attention due to their ability to improve chemical and thermal compatibility between electrolytes and electrodes and reduce manufacturing costs. The in-situ precipitating of electrode in reduction atmosphere has been proved to be an effective strategy to improve the maximum power density of SSOFCs. Herein, we use the Li(NixCo2/3-xMn1/3)O2 (LNCM) serial material as the symmetrical electrodes to fabricate SSOFCs, which are operated in normal and reverse mode. In reverse operation, the LNCM is firstly reduced by hydrogen and in-situ precipitates the Ni-Co alloy and Li2MnO3. The electrochemical impedance spectra (EIS) indicates that the reduced product delivers excellent oxygen reducing activity as well as promising catalytic activity toward hydrogen oxidation reaction. Thus, the SSOFCs based on LNCM symmetric electrodes present superior electrochemical performance in the reverse operation. Moreover, in the LNCM serial samples, the atomic ratio of Ni and Co at the B site is adjusted to control the contents of in-situ precipitation for further optimizing the cell performance. Using Li[Ni1/2Co1/6Mn1/3]O2 as symmetric electrodes shows outstanding performance of 923 mW·cm-2 at 550 °C. This work provides a reference scheme for electrode design of SSOFCs.
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