Showing papers in "Journal of Materials Research in 2021"
TL;DR: In this paper, the authors outline the basics of microwave dielectric ceramics alongside the mechanism of cold sintering and discuss future prospects and critical issues for advancing cold-sintered materials and devices, such as unclear mechanism, low Q'×'f values and poor mechanical properties.
Abstract: Microwave (MW) dielectric ceramics are used in numerous electronic components for modern wireless communication systems, including antennas, resonators, capacitors and filters. However, to date, MW ceramics are manufactured by an energy-intensive, conventional high-temperature (> 1000 °C) sintering technology and thus cannot be co-sintered with low melting point and base electrodes (Ag, Al, etc., < 1000 °C), nor directly integrated with polymers (< 200 °C). Cold sintering is able to densify ceramics at < 200 °C via a combination of external pressure and a transient liquid phase, reducing the energy consumed and facilitating greater integration with dissimilar materials. This review outlines the basics of MW ceramics alongside the mechanism of cold sintering. Recent developments in cold sintering of MW ceramics, composites and devices are described, emphasizing new materials and progress towards component/device fabrication. Future prospects and critical issues for advancing cold-sintered MW materials and devices, such as unclear mechanism, low Q × f values and poor mechanical properties, are discussed.
52 citations
TL;DR: The results of untiring efforts by the research community over the past few decades have led to the successful development and processing of a number of advanced titanium alloys with widely varying properties that can cater to niche applications.
Abstract: The results of untiring efforts by the research community over the past few decades have led to the successful development and processing of a number of advanced titanium alloys with widely varying properties that can cater to niche applications. Advanced titanium alloys on one hand challenge structural steels with their higher specific strength coupled with their low temperature capability down to 4 K and pose serious threat on the other hand to superalloys for long-term applications up to 773 K. An improved understanding of the processing-microstructure-mechanical property correlation led to the realization of large scale as well as performance critical titanium alloy products in space arena. Recent advances in additive manufacturing, wherein the desired components are directly 3D printed from pre-alloyed powders/wires have given a definite advantage for cost-prohibitive titanium alloys. This review article discusses challenges in the processing, mechanical properties and microstructure evolution of various grades of titanium alloys. It also provides useful information for researchers working on titanium alloys with a glimpse in to the recent advances in Ti alloys and transformation of scientific knowledge to technological advancements in products for space applications.
38 citations
TL;DR: A review of lead-free ferroelectric materials can be found in this article, where the challenges and current status of lead free ferroelectrics based on prospective applications are discussed.
Abstract: The year of 2021 is the 100th anniversary of the first publication of ferroelectric behaviour in Rochelle salt, focussing on its piezoelectric properties. Over the past many decades, people witnessed a great impact of ferroelectricity on our everyday life, where numerous ferroelectric materials have been designed and developed to enable the advancement of diverse applications. Now the driving forces for ferroelectric studies stem from regulations on environment, human health and sustainable society development. This leads to the resurgence of lead-free ferroelectric materials for the expectation of replacing the state-of-the-art lead-based counterparts. The next wave of explorations into ferroelectric materials maybe related to the Internet-of-Things, which requires millions of self-powered sensors and memories. This will promote research on ferroelectrics for sensing, energy harvesting and storage, communication and non-volatile memories, from centimetre scale to micro and nanoscale. This review gives a brief discussion from the materials viewpoint, on the challenges and current status of lead-free ferroelectrics based on prospective applications.
36 citations
TL;DR: In this article, two connection modes between ZIF-8 and ZIF67 frames in core-shell contact interface are proposed, and the corresponding photocatalytic mechanism is elucidated.
Abstract: Compared to single metal–organic framework (MOF), core–shell MOF crystals are more promising due to their special structure and unique properties. Herein, since ZIF-8 and ZIF-67 have the same topology, crystal growth method is used to synthesize core–shell crystals ZIF-8@ZIF-67, which exhibit far superior light adsorption, charge separation capabilities, and excellent stability than ZIF-8 and ZIF-67. The photocatalytic H2 generation rate for ZIF-8@ZIF-67 (1:1) is about 17 times higher than that of pure ZIF-67 without cocatalyst loading under same reaction conditions. Through a series of characterizations, two connection modes between ZIF-8 and ZIF-67 frames in core–shell contact interface are proposed, and the corresponding photocatalytic mechanism is elucidated. Transient photovoltaic curve reveals the unique transfer paths of electrons through contact interface, which leads to efficient charge separation compared with other ZIF materials. This study provides a novel and simple strategy to synthesis high effective and stable core–shell ZIF photocatalyst for photodegradation and hydrogen evolution.
27 citations
TL;DR: In this paper, high-speed nanoindentation mapping, electron probe microanalysis, and electron backscatter diffraction were employed to characterize as-deposited and heat-treated Ti-6Al-2Zr-Mo-V alloys.
Abstract: Titanium alloys are widely used in additive manufacturing, but their complex microstructures and related micromechanical properties have not been fully explored. Here, we employ high-speed nanoindentation mapping, electron probe microanalysis, and electron backscatter diffraction to characterize as-deposited and heat-treated Ti–6Al–2Zr–Mo–V alloys. Our results show the correlations between mechanical contrasts (hardness and elastic modulus) and phase contrasts (α and β). The hardness and elastic modulus of the α and β phases are increased due to the element redistribution after annealing (Al diffuses from β to α; Mo and V diffuse from α to β). We use a K-means clustering algorithm to analyze the nanoindentation dataset and correlate the mechanical property maps to the distribution of α and β phases. Our study employs the emerging high-speed nanoindentation mapping to give a better understanding of the microstructure–mechanical property relationship of additive manufactured multiphase alloys across length scales.
25 citations
TL;DR: In this article, the authors discuss the development of MBE from its beginnings as a method for III-V semiconductor growth to today for the growth of many contenders for next-generation electronics.
Abstract: Much progress has been made in the area of wide bandgap semiconductors for applications in electronics and optoelectronics such as displays, power electronics, and solar cells. New materials are being sought after and considerable attention has been given to complex oxides, specifically those with the perovskite crystal structure. Molecular-beam epitaxy (MBE) has come to the forefront of this field for the thin film synthesis of these materials in a high-quality manner and achieves some of their best figures of merit. Here, we discuss the development of MBE from its beginnings as a method for III–V semiconductor growth to today for the growth of many contenders for next-generation electronics. Comparing MBE with other physical vapor deposition techniques, we identify the advantages of MBE as well as many of the challenges that still must be overcome should this technique be applied to other up-and-coming wide bandgap complex oxide semiconductors.
23 citations
TL;DR: In this paper, a review of the development of hard lead-free piezoelectric ceramics for high-power applications is presented, including three different models mainly developed based on the lead zirconate titanate system.
Abstract: Ecologically sustainable development of piezoelectric ceramics has been the primary target of the community over the past 20 years. While the development of “soft” lead-free piezoelectric ceramics has been of high maturity, the understanding of “hard” lead-free piezoelectric ceramics is still far from satisfactory, leading to a limited chance for high-power applications. The review starts with an introduction of loss mechanisms and the hardening effect in piezoelectric ceramics, including three different models mainly developed based on the lead zirconate titanate system. Then, studies on the hardening behavior of BaTiO3-based, (Bi0.5Na0.5)TiO3-based, and (K0.5Na0.5)NbO3-based lead-free piezoelectric ceramics are summarized with emphasis on the approaches to enhance mechanical quality factor. Meanwhile, three different characterization methods of high-power performances are introduced: the constant-voltage method, constant-current method, and transient (or burst) method. Finally, the state-of-the-art lead-free ultrasonic transducer applications are highlighted. This paper concludes with the remaining challenges for the development of “hard” lead-free piezoelectric ceramics for high-power piezoelectric applications.
22 citations
TL;DR: In this paper, the thermodynamics of Al incorporation and its consequences on the electronic structure of Ga2O3 and Al 2O3 (AGO) alloys are discussed.
Abstract: Alloys between Ga2O3 and Al2O3 (AGO) present a rich material space exhibiting numerous structural phases with unique optoelectronic properties that make them attractive candidates as ultra-wide bandgap (UWBG) semiconductors for next-generation power devices. Here we review the properties of AGO, focusing on theoretical results on the thermodynamics of Al incorporation and its consequences on the electronic structure. We review predictions and progress in experimentally realizing these alloys, as well as how composition influences important optoelectronic variables such as the band gap, band offsets, transport properties, and n-type dopability. A number of these parameters, such as the breakdown field (related to the band gap) and electron mobility, are discussed in assessing AGO in terms of relevant power device figures of merit. Overall, the rapid progress and predicted properties highlight the promise of AGO as a model UWBG semiconductor platform with the potential to revolutionize power devices.
21 citations
TL;DR: In this paper, the authors present an updated overview of the various factors that affect the precision and accuracy of the nanoindentation test results at different test conditions with specific focus on the continuous stiffness measurement technique (CSM).
Abstract: The method to measure hardness and elastic modulus of small volumes of material by instrumented indentation was developed in the early works of Oliver and Pharr (1992, 2004). This helped to establish the field of small scale nanomechanical testing. Since then, several advances in measurement electronics have enabled testing over a wider range of test conditions (speeds) using methodologies that were developed earlier. Here, we present an updated overview of the various factors that affect the precision and accuracy of the nanoindentation test results at different test conditions with specific focus on the continuous stiffness measurement technique (CSM). A step-by-step procedure for performing a CSM based indentation test is presented. In addition, calibration procedures that yield the best possible precision and accuracy at the chosen test conditions are also presented. Finally, we present an assessment and comparison of the different testing procedures.
21 citations
TL;DR: In this article, a three-dimensional (3D) bone scaffold is designed with CAD software, it is controlled pore size, and porosity ratio and a systematic production process is followed.
Abstract: Tissue Engineering (TE) applications are focused on the design and fabrication of computer-aided artificial bone scaffolds with developing Additive Manufacturing (AM) technologies. Three-dimensional (3D) bone scaffold is designed with Computer-Aided Design (CAD) software, it is controlled pore size, and porosity ratio and a systematic production process are followed. In this study, artificial bone scaffold design and manufacturing technologies developed with AM technology have been discussed. The first part of the study is the applications materialized through different design methods such as CAD-based design, image-based design, implicit surface design, Topology Optimization (TO), and space-filling curves, which are used in computer-aided artificial bone scaffold design. Secondly, working principles of various AM technologies such as material extrusion and vat photopolymerization, powder bed fusion, material jetting, and direct writing and advantages and limitations of implementing these technologies in TE are also evaluated. Finally, possible future areas of use of the AM technologies in TE are discussed.
20 citations
Abstract: In this paper, we study the synthesis dependence of structural, optical and antimicrobial properties for copper oxide nanoparticles on, synthesized using microwave irradiation CuO(M), co-precipitation CuO(P) and hydrothermal CuO(H) protocols. Structural and morphological properties were studied using XRD, SEM, TEM and SAED techniques. XPS studies confirmed the presence of copper ions in Cu2+ oxidation state, and Raman spectroscopy confirmed the presence of nanostructured phase in all the samples. The synthesized CuO(M), CuO(P) and CuO(H) nanoparticles were investigated for antimicrobial activity against different pathogenic bacteria including methicillin-resistant Staphylococcus aureus. The result showed that maximum inhibition zone was detected in CuO(M) nanoparticles against Gram-negative bacteria i.e. Klebsiella pneumoniae (20 mm). CuO(H) and CuO(P) nanoparticles have antibacterial inhibition zone of 17 mm and 13 mm against K. pneumoniae and S. aureus, respectively. The CuO(P) and CuO(H) nanoparticles displayed mild antimicrobial activity as compared to the CuO(M) nanoparticles.
TL;DR: In this article, a polyvinylidene fluoride (PVDF)/SiO2 coating is successfully prepared with a simple dip coating method, which shows impressive superhydrophobic properties with a large water contact angle (WCA) of 159° and a small sliding angle (SA) of less than 3°.
Abstract: Superhydrophobic coatings have been regarded as potential promising solutions to many problems, e.g., ice accumulation in the winter seasons. To be practically useful and economically attractive, it is necessary to fabricate such coatings using facile methods, i.e., with minimal steps and low cost. In this work, a polyvinylidene fluoride (PVDF)/SiO2 coating is successfully prepared with a simple dip coating method. It shows impressive superhydrophobic properties with a large water contact angle (WCA) of 159° and a small sliding angle (SA) of less than 3°. Meanwhile, its superhydrophobic properties are robust in a large temperature range of – 30 to 350 °C and in various environments. Moreover, it shows remarkable anti-icing properties by delaying the freezing time (4 times) and reducing (40%) the adhesion of the ice on the substrate. Therefore, this work has displayed a promising approach for fabricating superhydrophobic coatings towards anti-icing applications.
TL;DR: In this article, the influence of the Al2O3 thickness, substrate temperature, and post-deposition anneal on surface passivation was investigated and the role of the GeOx interlayer as well as the presence of interface charges was addressed.
Abstract: Surfaces of semiconductors are notorious for the presence of electronic defects such that passivation approaches are required for optimal performance of (opto)electronic devices For Ge, thin films of Al2O3 prepared by atomic layer deposition (ALD) can induce surface passivation; however, no extensive study on the effect of the Al2O3 process parameters has been reported In this work we have investigated the influence of the Al2O3 thickness (1–44 nm), substrate temperature (50–350 °C), and post-deposition anneal (in N2, up to 600 °C) We demonstrated that an effective surface recombination velocity as low as 170 cm s−1 can be achieved The role of the GeOx interlayer as well as the presence of interface charges was addressed and a fixed charge density $${Q}_{\mathrm{f}}=$$
−(18 ± 05) × 1012 cm−2 has been found The similarities and differences between the passivation of Ge and Si surfaces by ALD Al2O3 prepared under the same conditions are discussed
TL;DR: In this paper, a high recoverable energy density of 4.3 J/cm3 and a high energy efficiency of 90% were simultaneously achieved in the ceramic capacitor at an applied electric field of 360 kV/cm.
Abstract: Sodium niobate (NaNbO3)‐based dielectrics have received much attention for energy storage applications due to their low‐cost, lightweight, and nontoxic nature. The field‐induced metastable ferroelectric phase in NaNbO3‐based dielectrics, however, leads to a large hysteresis of the polarization–electric field (P–E) loops and hence deteriorate the energy storage performance. In this study, the hysteresis was successfully reduced by introducing Bi3+ and Ti4+ into A‐site and B‐site of NaNbO3, respectively. MnO2 addition was added to further increase the ceramic density and enhance the cycling reliability. As a result, a high recoverable energy density of 4.3 J/cm3 and a high energy efficiency of 90% were simultaneously achieved in the ceramic capacitor at an applied electric field of 360 kV/cm. Of particular importance is that the ceramic capacitor exhibits a stable energy storage properties over a wide temperature range of −70 to 170 °C, with much improved electric cycling reliability up to 105 cycles.
TL;DR: It was revealed that the developed DDS has higher anti-cancer activity owing to its “smart” and slow drug release behavior as well as synergic effect of hyperthermia therapy.
Abstract: A novel magnetic pH- and redox-responsive drug delivery system (DDS) based on natural Tragacanth gum (TG) was developed for targeted chemo/hyperthermia treatment of cancer. Firstly, acrylic acid (AA) monomer was grafted onto a maleic anhydride-functionalized TG macromonomer (MATGM) through a free radical copolymerization. Magnetic nanoparticles (MNPs) were synthesized through chemical co-precipitation, and subsequently were modified using (3-aminopropyl)triethoxysilane coupling agent. The magnetic stimuli-responsive hydrogel for targeted cancer therapy was synthesized by the incorporation of modified-MNPs and folic acid (FA), and simultaneous crosslinking of TG-g-PAA copolymer using cystamine (Cys) moiety. Doxorubicin hydrochloride (Dox) was loaded into the fabricated magnetic hydrogel (MH), and its release was studied under pH- and redox-triggered condition. The anti-cancer activity of the Dox-loaded DDS was examined against MCF7 cells through MTT assay by both chemotherapy and chemo/hyperthermia therapy approaches. It was revealed that the developed DDS has higher anti-cancer activity (~ 24%) owing to its “smart” and slow drug release behavior as well as synergic effect of hyperthermia therapy. A novel magnetite pH- and redox-responsive drug delivery system (DDS) based on natural Tragacanth gum (TG) was design and developed for targeted chemo/hyperthermia therapy of solid tumors.
TL;DR: The zinc oxide (ZnO) nanostructures were synthesized using hydrothermal reaction technique at 180°C with varying reaction time viz., 2, 4, 8 and 12h and characterized with different spectroscopic/microscopic techniques as discussed by the authors.
Abstract: The zinc oxide (ZnO) nanostructures were synthesized using hydrothermal reaction technique at 180 °C with varying reaction time viz., 2, 4, 8 and 12 h and characterized with different spectroscopic/microscopic techniques. XRD indicate the formation of hexagonal phase of ZnO in all the prepared samples. The FESEM confirms the formation of hexagonal-shaped plate-like ZnO nanostructures having size in the range of 50 to 100 nm with the thickness of 10–15 nm, at 2 h reaction time. Further increase in the reaction time leads to increase in thickness of hexagonal ZnO plates resulting in formation of three-dimensional (3D) distorted spherical structures with facets. The photocatalytic activities were investigated by following degradation methylene blue (MB) dye. The ZnO prepared at 8 h of reaction time shows highest MB degradation rate, the apparent rate constant is 3.3 × 10–2 ± 0.1 × 10–2 min−1, almost five times more than 4 h reaction time. Photocatalytic dye degradation mechanism for two- & three-dimensional Zinc Oxide nanostructures on FESEM enlarge image of 8 h reaction time. Recycle study of MB degradation up to 5 recycles is shown (photographs of MB dye at time t0 and t120)
TL;DR: In this paper, a range of depth/spacing increments was explored on two different materials systems, an Al-Cu eutectic alloy and a duplex stainless steel, representing an easy and a hard case for statistical deconvolution, respectively.
Abstract: The development of high-speed nanoindentation has enabled the acquisition of mechanical property maps over square millimeters of area with micron-scale resolution in reasonable amounts of time. This provides rich datasets which contain morphological and statistical data on the variation of mechanical properties in a microstructure. However, the influences of the indentation size and the deconvolution method employed on the extracted phase properties remain unclear. In this work, a range of depth/spacing increments was explored on two different materials systems, an Al-Cu eutectic alloy and a duplex stainless steel, representing an ‘easy’ and a ‘hard’ case for statistical deconvolution, respectively. A total of ~ 500,000 indentations were performed. A variety of statistical analyses were then employed and compared: the 1D analysis of Ulm et al. using 2 and 3 phases, a 2D rotated Gaussian fit, K-means clustering, and a visual comparison to 2D histograms. This revealed several different sensitivities of the deconvolution methods to various types of error in phase identification.
TL;DR: In this paper, a method is presented for the registration and correlation of property maps of materials, including data from nanoindentation hardness, EBSD, and Electron Micro-Probe Analysis (EPMA).
Abstract: A method is presented for the registration and correlation of property maps of materials, including data from nanoindentation hardness, Electron Back-Scattered Diffraction (EBSD), and Electron Micro-Probe Analysis (EPMA). This highly spatially resolved method allows for the study of micron-scale microstructural features, and has the capability to rapidly extract correlations between multiple features of interest from datasets containing thousands of data points. Two case studies are presented in commercially pure (CP) titanium: in the first instance, the effect of crystal anisotropy on measured hardness and, in the second instance, the effect of an oxygen diffusion layer on hardness. The independently collected property maps are registered using affine geometric transformations and are interpolated to allow for direct correlation. The results show strong agreement with trends observed in the literature, as well as providing a large dataset to facilitate future statistical analysis of microstructure-dependent mechanisms.
TL;DR: In this article, a process-structure-property approach is used to systematically review the reported processes for ohmic contact formation on gallium oxide, the contact microstructure, and the resulting electrical properties including charge transport physics.
Abstract: β-Ga2O3 is a promising material for next-generation power devices because of its ultra-wide bandgap, the commercial availability of bulk substrates, epitaxial growth, and ease of n-type doping. To fully exploit its potential, it is critical to establish fabrication processes to form low-resistance ohmic contacts with excellent long-term stability. Due to upward band bending and unavoidable redox reactions occurring at the contact interface, making a good ohmic contact to gallium oxide can be challenging. Herein, we use a process-structure-property approach to systematically review the reported processes for ohmic contact formation on gallium oxide, the contact microstructure, and the resulting electrical properties including charge transport physics. Furthermore, we describe the present evidence for ohmic contact stability under accelerated aging. Using thermodynamic assessment, we propose alternate ohmic contact materials candidates. Finally, we identify gaps in the scientific knowledge on ohmic contacts to Ga2O3 and highlight opportunities for future investigations.
TL;DR: In this paper, the plastic deformation in a model nanocrystalline high entropy alloy (HEA), CoNiCrFeMn, is studied by using molecular dynamics simulations.
Abstract: In this work, the plastic deformation in a model nanocrystalline high entropy alloy (HEA), CoNiCrFeMn, is studied by using molecular dynamics simulations. It is found that the plastic deformation of nanocrystalline CoNiCrFeMn HEAs is dominated by a partially reversible face-centered cubic (FCC) to hexagonal close-packed (HCP) transformation mediated by stacking faults and partial dislocations, which is dramatically different from the full dislocation and deformation twinning-dominated plasticity in conventional FCC metals. This mechanism is strongly associated with the metastable nature of CoNiCrFeMn. Furthermore, although the transformed HCP structures can hinder the migration of the subsequent partial dislocations, they can penetrate each other to form a complicated stacking fault network, which is consistent with the recent experimental observations. Nevertheless, the nanocrystalline CoNiCrFeMn HEAs still show the conventional Hall–Petch breakdown when the grain sizes are reduced below a critical value. It is hoped that this study provides an atomistic insight into the plasticity of metastable HEAs and sheds some light on the design of novel HEAs for ultrahigh strength and plasticity.
TL;DR: In this paper, a 3D-printed active materials can be combined with an efficient computational framework to design large-scale lattice structures that can change their shape between an initial state and a target state.
Abstract: Active structures can adapt to varying environmental conditions and functional requirements by changing their shapes and properties, which makes them suitable for applications in changing environments as found in aerospace and automotive. Of special interest are light and stiff structures with shape morphing capabilities, which is naturally contradictory. Existing concepts in literature can be limited to a single, non-reversible actuation and are difficult to design due to the inherent complexity of large-scale lattices with many elements and complex target deformations. Here, we show how 3D-printed active materials can be combined with an efficient computational framework to design large-scale lattice structures that can change their shape between an initial state and a target state. The reversible deformation is controlled by a single actuation input and heating of the structure. Numerical and experimental results show the generality of the proposed method and the applicability to different problems such as morphing airfoils.
TL;DR: In this article, the authors report on the mechanical behavior of a solid Li-ion conductor, Li phosphorous oxynitride (Lipon), for solid-state batteries.
Abstract: We report on the mechanical behavior of a solid Li-ion conductor, lithium phosphorous oxynitride (Lipon), for solid-state batteries. In particular, the purpose of this investigation was to quantify the resistance to cracking (fracture toughness) of this material by nanoindentation. We observed surprising ductility and the ability to recover in Lipon. We were unsuccessful in inducing cracks in Lipon and observed accommodation of stress via pile-up and densification rather than by cracking at various strain rates. Simulations demonstrate that both deformation and densification depend on the alkali content. Densification appears to be recoverable at room temperature. We discuss the findings in comparison with nanoindentation-induced cracking in other inorganic solid electrolyte materials and provide possible explanations for high resistance of Lipon to Li filament propagation.
TL;DR: In this article, a copper selenide-based non-enzymatic sensor was used for co-detection of glucose and dopamine with high selectivity, which showed high reproducibility, reusability and long-term operational stability along with high degree of selectivity for dopamine and glucose sensing.
Abstract: Cu2Se, synthesized through one-pot hydrothermal synthesis, was identified as highly efficient bifunctional sensor for co-detection of glucose and dopamine with high selectivity. As-synthesized copper selenide could electro-oxidize glucose and dopamine at different applied potentials. Glucose oxidation was observed at 0.35 V while dopamine oxidized at 0.2 V. This copper selenide-based non-enzymatic sensor showed high sensitivity for both glucose (15.341 mA mM−1 cm−2) and dopamine (12.43 μA μM−1 cm−2) with low limit of detection (0.26 μM and 84 nM). Such high sensitivity and low LOD makes this sensor attractive for possible detection of glucose/dopamine in physiological body fluids which have low concentration of these biomolecules. Extremely low applied potential for detection also makes it ideal for integrating into wearable continuous monitoring devices with low operational power requirement. This sensor showed high reproducibility, reusability and long-term operational stability along with high degree of selectivity for dopamine and glucose sensing in presence of other interferents.
TL;DR: In this paper, an improved recoverable energy storage density (Wrec) of 4.8 J/cm3 was achieved for ANTA1 ceramics with 1 wt% Ag2O in excess, demonstrating obvious improvement compared with the stoichiometric counterpart.
Abstract: Lead-free dielectric capacitor with high energy storage density is in great demand, but with the challenge of limited energy storage density. In this work, Ag(Nb0.85Ta0.15)O3-x wt% Ag2O (ANTAx) lead-free ceramics with nonstoichiometric Ag2O were fabricated, with the aim of improving energy storage density. The element concentration, phase structure, microstructure, dielectric property, and energy storage performance were investigated. Improved recoverable energy storage density (Wrec) of 4.8 J/cm3 were achieved for ANTA1 ceramics with 1 wt% Ag2O in excess, demonstrating obvious improvement compared with the stoichiometric counterpart. In addition, the ANTA1 ceramics also exhibited highly stable energy storage performance in the temperature range from room temperature to 150 °C, with variations less than 4% and 5% for Wrec and energy storage efficiency, respectively. The good properties may be associated with the dismissing of various defects by adding excess Ag2O. This work demonstrates that silver stoichiometry engineering is an effective method to improve energy storage properties of AgNbO3-based antiferroelectric ceramics.
TL;DR: In this article, the synthesis and validation of the novel Ag-eugenol nanoemulsion (O/W) was dealt with, which was validated by DLS, TEM, FT-IR, UV-VIS spectral analysis; TEM reveals the particles an average size of 30-nm and SEM images confirm spherical morphology of particles.
Abstract: The current research deals with the synthesis and validation of the novel Ag-eugenol nanoemulsion (O/W). The synthesized Ag-eugenol nanoemulsion was validated by DLS, TEM, FT-IR, UV–VIS spectral analysis; TEM reveals the particles an average size of 30 nm and SEM images confirm spherical morphology of particles. Zeta potential measurements, presented a negative average zeta potential of − 25 mV. EDX analysis showed typical absorption peaks at 0.25 keV and 3 keV that confirm the presence of AgNPs. Elemental mapping of Ag-eugenol nanoemulsion confirms the presence of silver, eugenol moiety and the AgNPs are nucleated by eugenol moiety. Eugenol, eugenol nanoemulsion (5 µg/ml), AgNPs (25 ppm) and Ag-eugenol nanoemulsion (12.5 ppm AgNPs: eugenol 2.5 µg/ml) solutions were tested for their antimicrobial potency against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Proteus vulgaris. Ag-eugenol nanoemulsion was effective against both tested fungi; A. fumigatus and C. albicans with MIC 12.5:2.5 ppm:µg/ml and 6.25:1.25 ppm:µg/ml, respectively, comparing to a negative effect of eugenol nanoemulsion.
TL;DR: In this paper, double-cation based bismuth perovskite-inspired materials were developed by completely replacing CH3NH3+ (methylammonium, MA+) in MA3Bi2I9 with various organic cations such as CH(NH2)2+ (formamidinium, FA+), (CH3)2NH2+(dimethylammium, DMA+), C(NH 2)3+(guanidiniam, GA+) and inorganic cations, such as cesium (Cs
Abstract: Investigations on the effect of single or double A-site cation engineering on the photovoltaic performance of bismuth perovskite-inspired materials (A3Bi2I9) are rare. Herein, we report novel single- and double-cation based bismuth perovskite-inspired materials developed by (1) completely replacing CH3NH3+ (methylammonium, MA+) in MA3Bi2I9 with various organic cations such as CH(NH2)2+ (formamidinium, FA+), (CH3)2NH2+ (dimethylammonium, DMA+), C(NH2)3+ (guanidinium, GA+) and inorganic cations such as cesium (Cs+), rubidium (Rb+), potassium (K+), sodium (Na+) and lithium (Li+) and (2) partially replacing MA+ with Cs+ in different stoichiometric ratios. Compared to single-cation based bismuth perovskite devices, the double-cation bismuth perovskite device showed an increment in the device power conversion efficiency (PCE) up to 1.5% crediting to the reduction in the bandgap. This is the first study demonstrating double-cation based bismuth perovskite showing bandgap reduction and increment in device efficiency and opens up the possibilities towards compositional engineering for improved device performance.
TL;DR: In this article, the authors provide a review of Pb-free relaxors with particular reference to their dielectric properties and discuss the classical microscopic models of relaxors and discuss how these models have evolved over the last decade.
Abstract: Relaxors are complex oxide ferroelectrics that are of interest because of their attractive dielectric and electromechanical properties. A broad frequency-dependent dielectric permittivity peak is usually considered as a characteristic feature of relaxors. In spite of decades long research, a microscopic model of relaxors has not been conclusively established. In recent years, this field has experienced renewed interest driven by mainly two factors: (a) discovery of new Pb-free relaxors in response to toxicity concerns about Pb-based materials in electronics and (b) advancements in experimental and theoretical techniques that provided new microscopic insights. The objectives of the current review are the following. First, we will provide a description of some important Pb-free relaxors with particular reference to their dielectric properties. Second, we will review the classical microscopic models of relaxors and discuss how these models have evolved over the last decade. The opportunities in this regard provided by the emergence of new Pb-free relaxors will be highlighted.
TL;DR: In this article, the etching of β-Ga2O3, including regular wet etch, photoelectrochemical etching, reactive ion etching (RIE), and metal-assisted chemical etch (MacEtch), is reviewed.
Abstract: β-Ga2O3, a promising ultra-wide bandgap material for future high-power electronics and deep-ultraviolet optoelectronics applications, has drawn tremendous attention in recent years due to its wide bandgap of ~ 4.8 eV, high breakdown electric field, and availability of substrates. However, the reported etch behavior of β-Ga2O3 and the quality of etched surfaces, as well as the associated interface characteristics, could limit the performance of β-Ga2O3 devices. In this article, the etchings of β-Ga2O3, including regular wet etching, photoelectrochemical etching (PEC), reactive ion etching (RIE) and metal-assisted chemical etching (MacEtch), are reviewed. A comparison of the etch rate, orientation dependence, aspect ratio, etching mechanism, and surface quality for each of these etching methods is presented and the step-by-step reactions in PEC and MacEtch are proposed to elucidate the etch mechanism. The challenges for these etching techniques for β-Ga2O3 are discussed.
TL;DR: In this article, the authors focused on recent advances in the dislocation-GB interactions and underlying mechanisms studied via nanoindentation, which includes GB pop-in phenomenon, localized grain movement under ambient conditions, and an analysis of the slip transfer mechanism using theoretical treatments and simulations.
Abstract: To comprehend the mechanical behavior of a polycrystalline material, an in-depth analysis of individual grain boundary (GB) and dislocation interactions is of prime importance. In the past decade, nanoindentation emerged as a powerful tool to study the local mechanical response in the vicinity of the GB. The improved instrumentation and test protocols allow to capture various GB–dislocation interactions during the nanoindentation in the form of strain bursts on the load–displacement curve. Moreover, the interaction of the plastic zone with the GB provides important insight into the dislocation transmission effects of distinct grain boundaries. Of great importance for the analysis and interpretation of the observed effects are microstructural investigations and computational approaches. This review paper focused on recent advances in the dislocation–GB interactions and underlying mechanisms studied via nanoindentation, which includes GB pop-in phenomenon, localized grain movement under ambient conditions, and an analysis of the slip transfer mechanism using theoretical treatments and simulations.
TL;DR: In this paper, the authors developed the synthesis of Cr2C from its parent Cr2AlC MAX phase and showed the etching is optimized using sodium fluoride and hydrogen chloride with a modified minimally intensive layer delamination (mMILD) method in a cold environment of 9 ℃.
Abstract: MXenes are a large class of materials that are chemically exfoliated from metal–aluminum–carbon (MAX) bulk crystals into low-dimensional sheets. While many MXenes have been theoretically predicted, the careful balance required in the exfoliation between breaking the inter-layer bonds without damaging the intra-layer bonds of the sheets has limited synthesis and experimental study. Here, we developed the synthesis of Cr2C from its parent Cr2AlC MAX phase and showed the etching is optimized using sodium fluoride and hydrogen chloride with a modified minimally intensive layer delamination (mMILD) method in a cold environment of 9 ℃. We further optimized the intercalation and delamination using sonication and washing methods. The resulting Cr2C crystal structure was characterized. These results open up Cr2C to experimental study, including of its predicted emergent magnetic properties, and develop guidelines for synthesizing new MXene materials.