Modification Of Chemical Composition Research Articles

Investigation of Phase Transformations and Ordering Mechanisms in a Pd–Cu–Ag–Ru Alloy

An in‐depth analysis of phase transformations in a Pd–Cu–Ag alloy, crucial for applications in hydrogen membranes and electrical components, is presented. The investigation emphasizes the influence of the deformation rate and addition of Ag on the formation of the ordered CuPd phase. This study focuses on a specific alloy composition, 49.1% Cu–41.3% Pd–8.3% Ag–1.3% Ru, investigating its behavior under various conditions. Through comprehensive analysis, including the influence of the initial state, deformation variations, and chemical composition modifications, high‐energy X‐ray diffraction to unveil detailed phase evolution dynamics is used. Surprisingly, experimental findings deviate from the anticipated phase diagram, uncovering a previously unrecognized three‐phase region with the formation of AgPd. Notably, the study reveals the pivotal role of the alloy's Ag content in the development of ordered CuPd and AgPd phases. The addition of Ru exhibits no involvement in the observed phase transformations, contributing to the understanding of the alloy's composition‐dependent behavior. This research provides valuable insights into the intricate interplay of factors influencing phase transformations, offering a nuanced perspective beyond theoretical predictions. The newfound understanding of Ag's role and Ru's inertness refines material design considerations, enhancing the grasp of the alloy's thermodynamic stability under varying conditions.

From Insulator to Superconductor: A Series of Pressure-Driven Transitions in Quasi-One-Dimensional TiS3 Nanoribbons.

Transition metal trichalcogenides (TMTCs) offer remarkable opportunities for tuning electronic states through modifications in chemical composition, temperature, and pressure. Despite considerable interest in TMTCs, there remain significant knowledge gaps concerning the evolution of their electronic properties under compression. In this study, we employ experimental and theoretical approaches to comprehensively explore the high-pressure behavior of the electronic properties of TiS3, a quasi-one-dimensional (Q1D) semiconductor, across various temperature ranges. Through high-pressure electrical resistance and magnetic measurements at elevated pressures, we uncover a distinctive sequence of phase transitions within TiS3, encompassing a transformation from an insulating state at ambient pressure to the emergence of an incipient superconducting state above 70 GPa. Our findings provide compelling evidence that superconductivity at low temperatures of ∼2.9 K is a fundamental characteristic of TiS3, shedding new light on the intriguing high-pressure electronic properties of TiS3 and underscoring the broader implications of our discoveries for TMTCs in general.

Chitosan-supported calcium hydroxide hybrid material as new, efficient, and recyclable catalyst for biodiesel production

In this work, a novel supported catalyst was prepared starting from calcium chloride and chitosan flakes using a very mild approach in an aqueous medium without final calcination at high temperatures. The as-prepared catalyst was fully characterized by thermogravimetric analysis (TGA), attenuated total reflectance Fourier transform infrared (ATR-FTIR), and X-ray photoelectron (XPS) spectroscopies, transmission and scanning electron microscopies (TEM, SEM), Energy Dispersive X-ray Spectroscopy (EDS), demonstrating that it consists of calcium hydroxide particles of about 200 nm supported on chitosan micrometric structures. The most crucial parameters in the transesterification process were investigated. A methanol/oil ratio of 6:1, a reaction time of 6 h, and a temperature of 60 °C were found to lead to complete conversion. A reaction on a gram scale using waste oil as a starting material was also tested, and excellent results were achieved. Moreover, the catalyst proved to be very robust, since even after the 10th recycle, the conversion rate remained at around 90 %. Spectroscopic analyses showed minimal leaching of material without modification of chemical composition. The kinetic behavior (activation energy, Ea) of the catalyst was also studied, which resulted in similar outcomes to Ca-based systems present in the literature, but without the need for costly preparations and with superior recycling resistance. An Ea value of 63.25 kJ·mol−1 was found, which agrees with data reported in the literature.

Near‐infrared emitting metal halide materials: Luminescence design and applications

AbstractNear‐infrared (NIR) luminescent metal halide (LMH) materials have attracted great attention in various optoelectronic applications due to their low‐temperature solution‐processable synthesis, abundant crystallographic/electronic structures, and unique optoelectronic properties. However, some challenges still remain in their luminescence design, performance improvement, and application assignments. This review systematically summarizes the development of NIR LMHs through classifying NIR luminescent origins into four major categories: band‐edge emission, self‐trapped exciton (STE) emission, ion emission, and defect‐related emission. The luminescence mechanisms of different types of NIR LMHs are discussed in detail by analyzing typical examples. Reasonable strategies for designing and optimizing luminescence/optoelectronic properties of NIR LMHs are summarized, including bandgap engineering, self‐trapping state engineering, chemical composition modification, energy transfer, and other auxiliary strategies such as improvement of synthesis scheme and post‐processing. Furthermore, application prospects based on the optoelectronic devices are revealed, including phosphor‐converted light‐emitting diodes (LEDs), electroluminescent LEDs, photodetectors, solar cells, and x‐ray scintillators, as well as demonstrations of some related practical applications. Finally, the existing challenges and future perspectives on the development of NIR LMH materials are critically proposed. This review aims to provide general understanding and guidance for the design of high‐performance NIR LMHs materials.image

Porous titanium alloys for medical application: Progress in preparation process and surface modification research

Excellent mechanical properties and biocompatibility are the most sought-after attributes in biomedical materials for the regeneration of damaged tissues. However, conventional dense titanium alloys possess a modulus significantly higher than that of human tissues, leading to potential stress-shielding effects. Medical porous titanium alloys can reduce the elastic modulus of the material, promote tissue fixation and vascular regeneration, and improve the suitability for human tissue properties. With the continuous development of technology, the preparation process of porous titanium alloys has undergone a series of multifaceted transformations and improvements in the aspects of powder sintering, fiber preparation, and additive manufacturing processes, and its structural characteristics and mechanical properties are constantly evolving in a controllable direction. Alongside the enhancement of the material’s mechanical properties through porous design, optimization of the properties at the implant-tissue interface also leads to improved antimicrobial and osteogenic properties of porous titanium. Due to the complex internal structure of porous titanium alloys, surface modification is mainly carried out in fluid media, which is realized by morphological modification and the introduction of functional substances. Over time, the surface modification of porous titanium alloys for medical applications has progressed from morphological modification and introduction of chemical composition to the loading of bioactive substances. This evolution aims to enhance safety and efficiency in the use of these materials. This paper reviews the preparation and surface modification processes of porous titanium alloys for medical use and summarizes the advantages, disadvantages, and influencing factors among different processes, with a view to providing new ideas for the development of porous implants for medical use.

Influence of Post-Harvest 1-Methylcyclopropene (1-MCP) Treatment and Refrigeration on Chemical Composition, Phenolic Profile and Antioxidant Modifications during Storage of Abate Fétel Pears.

'Abate Fétel', a winter cultivar, is the most important pear cultivar in Italy; its fruits are appreciated by consumers for their aroma, texture and balanced sweet and sour taste. Maintaining high-quality characteristics to prolong the shelf-life of fruit and preserve the sensory and nutritional quality is a priority for the food industry. The aim of our study was to test the effectiveness of 1-methylcyclopropene (1-MCP) and cold storage in prolonging the shelf-life of these fruits, which were harvested at maturity at two different times. This work focused on the effects of different storage treatments and two ripening times on (i) the chemical composition of Abate Fétel pulp fruits to preserve their sweet taste and aroma and (ii) the phenolic profile composition and antioxidant activity of the peel, which is naturally rich in phytochemicals and important for the fruit's shelf-life and in the functional food industry for its high nutritional value. Abate Fétel fruits were harvested at the optimal commercial maturity stage, first on 15 September, having been treated with 1-MCP and stored for 2 months at cold temperatures; the other fruits were harvested at the end of September and stored in a cold cell for 2 months. The fruit pulp was tested for glucose and fructose, pH, acidity and organic acids (malic, citric, fumaric and shikimic), phenolic content and phenolic compounds (chlorogenic and caffeic acids, rutin, hyperoside, kaempferol-3-rutinoside and isoquercitrin), and the antioxidant activities in the fruit peels were measured. Treating the fruits with 1-MCP better preserved the phytochemical compounds compared to simple refrigeration, preserving the fruit's quality and prolonging its shelf-life. All the treatments help to maintain the glucose and fructose content and the acidity, preserving the aroma and organoleptic characteristics.

Effect of the Pulsed Electric Field Treatment on Physical, Chemical and Structural Changes of Vacuum Impregnated Apple Tissue in Aloe Vera Juices

Vacuum impregnation (VI) stands as a diffusion-driven food processing method that has found recent application within the food industry, particularly for the cold formulation of fortified food products. Pulsed electric field (PEF) treatment can affect the food structure, influencing therefore the mass transfer phenomena during the further processing. Thus, the study aimed at investigating the effect of PEF treatment on selected physicochemical properties of vacuum-impregnated apples. Apple slices were vacuum impregnated with aloe vera juice solution with or PEF treatment at different intensities (125, 212.5 or 300 V/cm). The PEF was applied as a pretreatment—applied before the VI process as well as posttreatment—applied after the VI process. The VI process with aloe vera juice resulted in a sample weight increase of over 24% as well as structural changes, partial cell viability loss and color alteration. In addition, the decrease of bioactive compounds was observed, while antioxidant activity remained at a similar level as in raw material. PEF treatment adversely affected vacuum impregnation efficiency, causing microstructural changes and cell viability loss. Additionally, chemical composition modifications were evident through thermogravimetric analysis (TGA) and Fourier Infrared Spectroscopy (FTIR) analyses. Tissue hardness decreased significantly due to structural damage and caused high leakage from plant tissue, which resulted in hindering saturation with aloe vera juice during the VI process. Additionally, reduced bioactive substance content after PEF treatment was observed and the VI process did not restore apple samples of the bioactive compounds from aloe vera juice.

Effect of Underlayer Quality on Microstructure, Stoichiometry, and Magnetic Properties of Hexaferrite BaFe12O19 Grown on YSZ(111) by Pulsed Laser Deposition.

We have studied the effect of platinum underlayer for two deposited thicknesses on the microstructure, crystalline quality, morphology, chemical composition, and magnetic properties as well as magnetic domain formation of BaFe12O19 (BaM) grown on YSZ(111) by pulsed laser deposition (PLD). We found that PLD platinum deposited with a thickness of 25 nm cannot withstand the dewetting phenomenon occurring during the subsequent BaM layer growth. A smooth and continuous Pt underlayer that possesses a sharp interface and omits the intermixing between the BaM and substrate was successfully achieved for a deposited Pt film thickness of 75 nm. Independent of the thickness of the deposited Pt layer, the c-axis orientation as well as coercivity Hc and the anisotropy HA fields were significantly improved due to a remarkable improvement of lattice mismatch in comparison with the BaM layer grown without a Pt underlayer on YSZ(111). By applying high-resolution X-ray diffraction, scanning and transmission electron microscopy (SEM/TEM), and atomically resolved scanning TEM imaging combined with energy-dispersive X-ray spectroscopy, as well as atomic and magnetic force microscopy, a comprehensive investigation of both structure and chemical composition of the deposited BaM films and their interfacial regions was performed. This study aimed to correlate the enhancement of the overall magnetic properties and of the local spin magnetic domain orientation with the modification of BaM microstructure and chemical composition at the nanometer scale due to the Pt underlayer. Finally, we attempted to understand the mechanisms that control the magnetic properties of these BaM films in order to be able to tailor them.

An updated overview of some factors that influence the biological effects of nanoparticles.

Nanoparticles (NPs) can be extremely effective in the early diagnosis and treatment of cancer due to their properties. The nanotechnology industry is developing rapidly. The number of multifunctional NPs has increased in the market and hundreds of NPs are in various stages of preclinical and clinical development. Thus, the mechanism underlying the effects of NPs on biological systems has received much attention. After NPs enter the body, they interact with plasma proteins, tumour cell receptors, and small biological molecules. This interaction is closely related to the size, shape, chemical composition and surface modification properties of NPs. In this review, the effects of the size, shape, chemical composition and surface modification of NPs on the biological effects of NPs were summarised, including the mechanism through which NPs enter cells, the resulting oxidative stress response, and the interaction with proteins. This review of the biological effects of NPs can not only provide theoretical support for the preparation of safer and more efficient NPs but also lay the foundation for their clinical application.

Cu-Content La1−XSrxNi1−YCuyO3−Δ Perovskites As Cobalt-Free Cathode Materials for High-Performance It-SOFCs

Solid Oxide Fuel Cells (SOFCs) are one of the most attractive energy conversion and storage devices, which can be applied for decentralized energy applications. However, the high operating temperature making SOFCs still unmarketable, which indicates that lowering the working temperature of SOFCs while still maintaining a high-power output is very crucial. For Intermediate-Temperature Solid Oxide Fuel Cells (IT-SOFCs), new cathode materials with high electrocatalytic activity and stability are necessary to provide a stable and high performance of cells. Perovskite-structured oxide (ABO3−δ) is one group of the most interesting material candidates for IT-SOFCs, presenting great potential in chemical composition modifications, yielding the design and gain of desired physicochemical and electrochemical properties [1]. The simple perovskite LaCuO3 is one of the well-studied Cu-content oxides with a high conductivity (106 S·cm−1), but it can be hardly obtained and suffers with stability issues in air [1, 2]. To stabilize the perovskite structure and to improve electrochemical properties of Cu-content oxides A-site and B-site modification strategy can be applied. It has been noted that Cu- and Ni-containing LaNi0.5Cu0.5O3−δ simple perovskite possesses low cathodic polarization of 0.056 Ω·cm2 at 800 °C, and a high power output of 870 mW·cm−2 at 900 °C [1, 3]. The generation of oxygen vacancies by strontium doping contributes to the increase of ionic conductivity component, and the Sr dopant can reduce the oxygen vacancy formation energy and increase the ionic conductivity of La1−xSrxMO3−δ (M = Fe, Mn) perovskites [1,4]. Therefore, in this work, Cu-content La1−xSrxNi1−yCuyO3−δ oxides with strontium doping at the A-site were evaluated as very promising Co-free cathode material candidates for IT-SOFCs.In this work, all La1−xSrxNi1−yCuyO3−δ compounds have been successfully obtained using soft chemistry. The room-temperature crystal structure of all oxides was assigned to the R-3c trigonal system. The substitution of La with Sr lowers the phase transition temperature from the R-3c space group to Pm-3m simple perovskite while increases the oxygen non-stoichiometry and the thermal expansion coefficient of studied materials. All investigated materials are chemically compatible with GDC-10, while unstable in contact with LSGM and 8YSZ. The manufactured anode-supported IT-SOFC with the La0.95Sr0.05Ni0.5Cu0.5O3−δ cathode presents an excellent power density of 445 mW·cm−2 at 650 °C in humidified H2. The results confirmed that La1−xSrxNi1−yCuyO3−δ perovskites can be potentially qualified as promising cathode candidates for IT-SOFCs, yielding promising electrochemical performance in the intermediate-temperature range [1].

Salt Stress Tolerance in Medicinal and Aromatic Plants: A Review

Soil salinity is a globally pervasive issue, significantly affecting crop productivity and quality. This review provides a comprehensive overview of salt stress tolerance in medicinal and aromatic plants, plants known for their unique metabolic capabilities and resilience to abiotic stress. The adverse impact of salt stress on plant development, growth, and chemical composition is examined, emphasizing the specific effects on medicinal and aromatic plants, such as reduced biomass, altered yield, and modification of chemical composition. We delve into the complex responses exhibited by plants under salt stress, including physiological, biochemical, and molecular mechanisms. Physiological responses such as osmotic adjustment and ion homeostasis, biochemical responses including antioxidant production and compatible solute synthesis, and molecular responses like the upregulation of salt stress-responsive genes and hormone modulation, all contribute to salt stress tolerance. Understanding these intricate mechanisms offers valuable insights into the plants' resilience under salt stress. This review also discusses strategies to enhance salt stress tolerance in medicinal and aromatic plants, encompassing breeding and genetic modification, management strategies, and the utilization of beneficial soil microbes. The potential of selective breeding and genetic engineering in developing salt-tolerant plants is explored, along with the implementation of efficient irrigation systems and the use of salt-tolerant rootstocks. Additionally, the potential role of beneficial soil microbes such as mycorrhizal fungi and plant growth-promoting rhizobacteria in alleviating salt stress is highlighted. Lastly, we present potential future directions and applications for this research. The findings and strategies elaborated upon in this review have far-reaching implications, including the improvement of salt stress tolerance in other crops, promoting sustainable agriculture in saline soils, and potential therapeutic implications due to altered biochemical composition under salt stress. The continuation of research in this field is critical to tackling soil salinity challenges and maximizing the medicinal and aromatic plants' potential under salt stress. This review underscores the importance of studying salt stress tolerance mechanisms in medicinal and aromatic plants to contribute to sustainable agricultural practices and the advancement of the pharmaceutical industry.

Novel Strategy for Surface Modification of Titanium Implants towards the Improvement of Osseointegration Property and Antibiotic Local Delivery

The topography and chemical composition modification of titanium (Ti) implants play a decisive role in improving biocompatibility and bioactivity, accelerating osseointegration, and, thus, determining clinical success. In spite of the development of surface modification strategies, bacterial contamination is a common cause of failure. The use of systemic antibiotic therapy does not guarantee action at the contaminated site. In this work, we proposed a surface treatment for Ti implants that aim to improve their osseointegration and reduce bacterial colonization in surgery sites due to the local release of antibiotic. The Ti discs were hydrothermally treated with 3M NaOH solution to form a nanostructured layer of titanate on the Ti surface. Metronidazole was impregnated on these nanostructured surfaces to enable its local release. The samples were coated with poly(vinyl alcohol)-PVA films with different thickness to evaluate a possible control of drug release. Gamma irradiation was used to crosslink the polymer chains to achieve hydrogel layer formation and to sterilize the samples. The samples were characterized by XRD, SEM, FTIR, contact angle measurements, "in vitro" bioactivity, and drug release analysis. The alkaline hydrothermal treatment successfully produced intertwined, web-like nanostructures on the Ti surface, providing wettability and bioactivity to the Ti samples (Ti + TTNT samples). Metronidazole was successfully loaded and released from the Ti + TTNT samples coated or not with PVA. Although the polymeric film acted as a physical barrier to drug delivery, all groups reached the minimum inhibitory concentration for anaerobic bacteria. Thus, the surface modification method presented is a potential approach to improve the osseointegration of Ti implants and to associate local drug delivery with dental implants, preventing early infections and bone failure.

Calculation of emission spectra of lithium compounds

AbstractWe studied the electronic structure of lithium metal, lithium fluoride, and spodumene using density functional theory. We performed calculations of the total, local and partial density of states, and x‐ray emission spectra. We observed changes in the Li K spectra shape and energy position due to the chemical structure and composition modification. We also outline possible interferences between emission bands.

Effect of forging sequence and heat treatment on microstructure of high-duty power-plant shaft made of Cr-Mo ultra-high strength steel

The paper presents results of modeling and testing of a heavy weight part made of Cr-Mo, which was V-modified ultra-high strength steel grade AISI 4140, processed through a novel open-die forging schedule and two alternative routes of two-stage heat treatment cycles designed to meet requirements of high-duty components for energy sector. Taking advantage of unconventional forging conditions based on assumption of large feed and reduction ratios and the modification of chemical composition better control of austenite grain was achieved to minimize abnormal grain growth and/or strain uniformity problems. With aid of Finite Element Modeling of multi-stage sequence of upsetting and cogging strain distribution was optimized so as to minimize strain fluctuations on the length to range 2.2?2.7,and correlated with microstructure produced at every major stage on the large cross-sections of the shaft. Designed with aid of finite element method processing cycles was verified in full-scale physical modeling with use of 16 ton forging ingot, including two alternative quenching strategies: oil vs. water spray and air. Examination of material in as-forged, normalized and heat-treated condition was carried out to observe response of hot-worked material and the effect of cooling conditions on microstructure during final heat treatment. As observed, employing large feed ratios on cogging and varied cooling allowed suppress detrimental effect of inevitable abnormal grain growth which resulted in 1-2 ASTM grain in as-forged conditions to reach 6 ASTM in normalized and 8/9 ASTM after quenching in oil and water spray, respectively, which allows producing after tempering, correspondingly, 44?48 and 85?122 J/cm2 V-notch impact strength in the critical area of the forged shaft.

Does Portuguese pharmaceutical market follow an innovative trend? The INFOMED database analysis

Abstract Background Product innovation in the pharmaceutical market is, although not exclusively, a new product with the capacity to generate value. Thus, it must represent an invention through investment in research and development, and not a commercial monopoly. The aim is to identify innovation trends by Marketing Authorization (MA) granted in Portugal. Methods Quantitative descriptive study based on data (years 2017 to 2021) from Human Medicinal Products Database (INFOMED), managed by the National Authority of Medicines and Health Products, I.P. The parameters identified and used were MA and medical product subject to medical prescription. List was filtered by Product Group - New Active Substance. To identify innovation, findings were compared with the Anatomical Therapeutic Chemical (ATC) database and scientific literature to find other therapeutic options available. Results A total of 2695 records were identified. 1804 (67%) were generic drugs. Regarding new substances, 46 registrations (1.7%) were obtained, with the highest number recorded in 2017 (n = 13 - 2.03%) and the lowest in 2019 (n = 3 - 0.76%). After exclusion of different concentrations with the same therapeutic indication, a total of 26 medicines were observed: 54% had a listed ATC code and those, 64% had more than two linked ATC codes; 12 medicines had no related ATC code and 5 were classified as vaccine and therefore were not considered, thus 7 medicines were classified as major innovation. Conclusions Most of the innovation seen in the pharmaceutical market is not major innovation, but rather due to structural changes to chemical compositions. The Portuguese scenario is no different. Generic drugs, although not innovative, are important in the pharmaceutical market from a public health perspective. The identified innovations, although not major innovations, are important from a clinical and market availability perspective, however they should not represent a large portion of the pharmaceutical market. Key messages • In Portugal, the innovation trend in the pharmaceutical industry is based essentially on modifications in chemical composition and related therapeutic class. • The development of major innovation in medicines should be stimulated and new models of financing and sustainability should be improved.

Effect of enzymatic process on characteristics of cottonized industrial hemp fibre

This paper reports an investigation on the bacteria-based enzyme's cottonization of industrial hemp fibre. The industrial hemp fibres are enzyme processed to eliminate massive non-cellulosic portions from the fibre to enhance their fineness and softness. Box- Behnken response surface methodology is applied to optimize the effect of different concentrations, temperature and time by using enzymes on chemical and physical properties, like weight loss, average strength, length, chemical composition, and surface modification to simulate cotton feel touch. The results show that the pectin, lignin, hemicellulose, and other impurities are removed under the enzyme and alkali refining processes. The effect of the enzyme concentration, treatment time, and treatment temperature is found significant on weight loss, fibre diameter, crystallinity, cellulose, hemicelluloses content, and tenacity. The effluent load of the enzyme process by measuring COD is also found less than that of the alkali processing for industrial hemp fibre. Industrial hemp fibre can be a perfect model of the sustainability of fibre from the plant's inception into the entire life cycle, leading to the biodegradable product reducing less effluent load in an environment.

Flexible Ferroelectric Materials-Based Triboelectric Nanogenerators for Mechanical Energy Harvesting

Triboelectric nanogenerators are widely used in a variety of applications including wearable electronics, self-driven sensors, electrochemistry, and other fields. A lot of work has been done by researchers to increase the performance of triboelectric nanogenerators. Changing device structure, physical surface engineering and chemical composition modification are common effective methods. Some recent studies have found that the polarization of ferroelectric materials can regulate the output of triboelectric nanogenerators. Compared with other materials, ferroelectric materials have the advantages of polarization characteristics and large dielectric constant, which can improve the output performance by regulating the electric potential on the surface of the material, and can also collect the pyroelectric -piezoelectric-triboelectric coupling energy. However, most ferroelectric materials are rigid and therefore difficult to apply to flexible wearable electronics. In this paper, we briefly describe the mechanism of ferroelectric polarization triboelectric output and the working mechanism of coupled generators, then introduce some flexible ferroelectric materials and finally introduce some of their recent applications.

9–12% Cr Heat-Resistant Martensitic Steels with Increased Boron and Decreased Nitrogen Contents

As a promising alloying approach, the modification of chemical composition by increasing the B content and decreasing the N content has been applied to improve the creep resistance of various 9–12% Cr heat-resistant martensitic steels. This paper presents an overview of the creep strength and related microstructural features of the 9% Cr and 10–12% Cr martensitic steels with high B and low N contents. The factors that determine the optimal B/N ratio in steels are considered. The creep properties are compared with those for similar steels with conventional B and N contents. The relationships between the stability of lath structure and precipitates of M23C6, Laves, and MX phases and the creep strength of steels are considered. Further perspectives of this modification of alloying by high boron and low nitrogen are outlined.

Enhancement of Nonlinear Dielectric Properties in BiFeO3-BaTiO3 Ceramics by Nb-Doping.

BiFeO3–BaTiO3 (BF–BT) ceramics exhibit great potential for diverse applications in high temperature piezoelectric transducers, temperature-stable dielectrics and pulsed-power capacitors. Further optimization of functional properties for different types of applications can be achieved by modification of processing parameters or chemical composition. In the present work, the influence of pentavalent niobium substitution for trivalent ferric ions on the structure, microstructure and dielectric properties of 0.7BF–0.3BT ceramics was investigated systematically. Doping with niobium led to incremental reductions in grain size (from 7.0 to 1.3 µm) and suppression of long-range ferroelectric ordering. It was found that core-shell type microstructural features became more prominent as the Nb concentration increased, which were correlated with the formation of distinct peaks in the dielectric permittivity–temperature relationship, at ~470 and 600 °C, which were attributed to the BT-rich shell and BF-rich core regions, respectively. Nb-doping of BF–BT ceramics yielded reduced electronic conductivity and dielectric loss, improved electrical breakdown strength and enhanced dielectric energy storage characteristics. These effects are attributed to the charge compensation of pentavalent Nb donor defects by bismuth vacancies, which suppresses the formation of oxygen vacancies and the associated electron hole conduction mechanism. The relatively high recoverable energy density (Wrec = 2.01 J cm−3) and energy storage efficiency (η = 68%) of the 0.7BiFeO3–0.3BaTiO3 binary system were achieved at 75 °C under an electric field of 15 kV mm−1. This material demonstrates the greatest potential for applications in energy storage capacitors and temperature-stable dielectrics.

Synergic effect of additives on the structure and properties of nano strontium hexaferrite synthesized via the gel combustion method

Strontium hexaferrite (SrFe12O19) is a ferrimagnetic oxide that is widely used as a permanent magnetic material due to its excellent magnetic properties and low production cost. Modification of chemical composition and nanoscale structural refinement can improve its properties. In the present study, the synthesis process of strontium hexaferrite by the gel combustion method was investigated. SrFe12O19 was synthesized with the iron to strontium ratio of 10-12. The calcination temperature was also optimized by modifying this ratio. The effect of adding cobalt, manganese, zirconium, and zinc cations to the composition of SrFe12-2x(Mn Co Zn)x/3ZrxO19 (x = 0.0–1.0) was investigated. The samples were characterized by X-ray diffraction (XRD), thermal analysis (TGA/DTA), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometer (VSM), and vector network analyzer (VNA). The results showed that, in the free-additive samples, the pure strontium hexaferrite phase was formed only under the optimal conditions where the iron to strontium ratio and heat-treatment temperature were about 11 and 900 °C, respectively. In this case, clustered particles with the size of 64-145 nm were observed in the structure. In addition, partial substitution of different amounts of manganese, cobalt, zinc, and zirconium cations for Fe3+ in the hexaferrite structure affected its magnetic properties, such as saturation magnetization (Ms), remnant magnetization (Mr), coercivity (Hr), and Mr/Ms ratio. The dielectric constant, reflectance, transmittance, and absorption of electromagnetic waves were also changed. The sample with x = 0.8 showed the maximum reflectance (36.20%) and minimum transmittance (54.10%). The sample with x = 0.4 showed the desired reflectance loss of −9.24 dB at the frequency of 12.15 GHz.