Controlling densification and grain growth during sintering is vital for optimizing the functionality of electroceramics. Here, defining the optimal temperature for Spark Plasma Texturing (SPT) - a pressure-driven, edge-free variant of spark plasma sintering (SPS), we investigate the influence of SPT processing parameters on the final properties of the tunable ferroelectric Ba0.6Sr0.4TiO3 ceramics. Systematically varying the pre-sintering route from conventional sintering to SPS and the onset temperature of pressure application from room temperature to 900 degrees C, we find that all SPT-processed ceramics reach densities >98.6% and possess ultrafine grains of 0.44-0.76 & micro;m. The highest dielectric permittivity, tunability and k-factor at minimized losses are obtained, however, on the near-theoretically dense ceramics prepared using conventionally pre-sintered pellets subjected to pressure from room temperature in the SPT process. These findings establish SPT as a powerful pathway for mechanically assisted microstructural engineering, offering new opportunities to design high-performance tunable dielectrics, with reduced grain growth and tailored dielectric properties, for adaptive microwave and electronic devices.

Dielectric breakdown strength (E-bd) defines the reliability and energy density of functional oxide ceramics in high-field applications. Here, we demonstrate that Spark Plasma Texturing (SPT) dramatically enhances E-bd in Ba0.6Sr0.4TiO3 (BST) ceramics. Dynamic thermo-mechanical coupling during SPT produces a near-fully dense, highly homogeneous microstructure with ultra-fine grains (0.44 mu m), resulting in E-bd of up to 515 kV & centerdot;cm(-1), which is more than twice higher than 200 kV & centerdot;cm(-1) for conventionally sintered ceramics and one third higher than 384 kV & centerdot;cm(-1) for ceramics prepared by standard Spark Plasma Sintering. This enhancement is of extrinsic origin and grain-boundary-controlled: impedance spectroscopy reveals elevated activation energies and resistive grain-boundary barriers that suppress long-range charge migration, while the intrinsic electronic structure with bandgap similar to 3.0 eV remains unchanged. SPT is thus established as an effective route for grain-boundary engineering in functional oxides, enabling high-reliability energy storage and tunable radio-frequency devices.

K0.5Na0.5NbO3-Bi(Zn2/3(Nb0.85Ta0.15)1/3)O3 ceramics were claimed by Zhang et al. in Chem. Eng. J. 425 (2021) 131465 to exhibit high energy storage performance promising for dielectric capacitor applications. However, here we express concerns regarding the discrepancies in the results presented to support these claims as well as ambiguity in the proposed physical mechanisms. We also highlight contradictions in the data analyses and a lack of important experimental details.

Dielectric breakdown strength (Ebd) limits the reliability and energy density of functional oxide ceramics in high-field applications. Here, we demonstrate that Spark Plasma Texturing (SPT) dramatically enhances Ebd in Ba0.6Sr0.4TiO3 (BST) ceramics. Dynamic thermo-mechanical coupling during SPT produces a near-fully dense, highly homogeneous microstructure with ultra-fine grains (0.44 μm), resulting in Ebd of up to 515 kV·cm−1, which is more than twice higher than 200 kV·cm−1 for conventionally sintered ceramics and one third higher than 384 kV·cm−1 for ceramics prepared by standard SPS. This enhancement is of extrinsic origin and grain-boundary-controlled: impedance spectroscopy reveals elevated activation energies and resistive grain-boundary barriers that suppress long-range charge migration, while the intrinsic electronic structure with bandgap ~ 3.0 eV remains unchanged. SPT is thus established as an effective route for grain-boundary engineering in functional oxides, enabling high-reliability energy storage and tunable radio-frequency devices.

The anodization of aluminium/aluminium alloys is widely used to produce anodic nanoporous networks for metal layered structures, with applications in energy harvesting technologies and sensor systems. Anodic aluminium oxide (AAO) with thickness of ~10 μm and average pore diameter of 13, 33, and 95 nm is prepared by tuning acids and voltages, being further used for electroless nickel deposition, performed for 10 min using conventional electrolyte with sodium hypophosphite reductor and pH 4.5. The formation of Ni nanotubes or nanorods is found to be strongly dependent on AAO pore size. Ni is detected in the whole pore depth and found to form 5–7 μm long continuous tube-like structures only in AAO with pore diameter of 95 nm, being kept just on the AAO top for smaller pore diameters. Nickel distribution in pores along cross-section of AAO is studied as well revealing continuously decreasing ratio to phosphorus amount. The magnetic properties of the resulting Ni 3D structure of a flat conductive layer and nanotubes perpendicular to it do not show significant differences in parallelly and perpendicularly oriented magnetic fields. These observations are discussed considering possible formation mechanisms for an electroless deposited Ni layer on AAO with different structures.

As the dynamic development of human–machine interfaces increases the demand for interactive sensors, this work demonstrates the successful fused filament fabrication of mutual capacitance sensors on acrylonitrile butadiene styrene substrates using conductive polylactic acid filament. The capacitor electrode infill density and infill pattern were selected as the two main variables to study their effects on the electrical behavior of the printed sensors. The variation in density is found to affect the electrode structure and, consequently, the resistance of the sensor electrodes, while changes in the infill pattern do not significantly alter it. The capacitance of the sensors is found to range from 0.5 to 2.2 pF, without and with external, controlled stimuli, respectively, and is independent of both the infill density and pattern. This capacitive behavior suggests that these variables can be optimized for the production of low-cost mutual capacitance sensors, minimizing both material use and production time.

Low sintering temperatures are essential for the sustainable development of ceramics and ceramic-based composites with the Cold Sintering Process (CSP) emerging as a promising technique. However, the formation of secondary phases, densification issues and functional behaviour may hinder its full potential. Here, we introduce a novel approach to the fabrication of dielectric composite thick films by combining CSP with a solvent-free polymer fibrillation process using polytetrafluoroethylene (PTFE). As proof of concept, we demonstrate a multilayer ceramic capacitor (MLCC) prototype based on BaTiO3-PTFE (similar to 3 wt%) fibrillated composite films with Ag screen-printed electrodes, processed omitting burnout step by CSP at 250 degrees C using Ba(OH)(2)8H(2)O as the transient phase. The resulting electrical performance of the MLCC prototype exhibits temperature stability, satisfying X8R capacitor grade requirements, and reduced dielectric losses. Additionally, a parallel-plate tunable capacitor is also designed using Ba1-xSrxTiO3-PTFE fibrillated thick films on copper foil, co-fired in a single step by CSP under the same conditions. Overall, these findings highlight the potential of CSP in bridging the gap between processing temperatures and the integration of polymers, metals and ceramics.

Current regulations pushing for lead-free piezoelectric alternatives have highlighted potassium-sodium niobate (K0.5Na0.5NbO3, KNN) as a promising candidate. However, conventional sintering of KNN faces challenges like alkali element volatilization and inadequate densification. Ultrafast high-temperature sintering (UHS) offers a solution by rapidly heating ceramics, yielding fine microstructures, with minimal volatile element loss. Here, using a custom UHS equipment we produced undoped KNN ceramics, identifying optimal sintering conditions via a UHS processing map. UHS KNN ceramics sintered for <= 90 s achieved 91 % density, <2 mu m average grain size, and no secondary phases. This study reports also the first dielectric, piezoelectric, and ferroelectric properties of UHS KNN ceramics. Differences between as-UHS and post-annealed ceramics were observed as well, with the latter exhibiting piezoelectric coefficients of similar to 80pC/N. This research enhances understanding of UHS applications and potential of KNN for lead-free piezoelectric uses.

SrTi2O5 particles were claimed by Panda et al. in J. Materiomics 2023; 9:609 as a new lead-free ferroelectric material with orthorhombic symmetry and space group of Cmm2, being, therefore, employed as a base of piezoelectric energy harvesters. However, in this comment we express concerns regarding the presence of the piezoelectricity in the studied material and the interpretation of the structural, microstructural, and ferroelectric results in that publication as those associated with SrTi2O5. We also note that the presented dielectric results are contradictory and that many important details are missing.

Ba1-xSrxTiO3 compounds are widely recognized as leading dielectric materials for tunable electronic applications. To expand their applicability and enable integration with polymers and metals, there is a need for low-temperature processing. Here we show that Cold Sintering Process (CSP) enables the fabrication of Ba0.6Sr0.4TiO3 (BST) tunable dielectric ceramics, using Ba(OH)(2)8 H2O as a flux, at a temperature as low as 350 degrees C. A dielectric permittivity with a low magnitude of similar to 340 at 10 kHz, an electric-field tunability of 11%, and a thermal stability of +/- 7.1% over the temperature range of -90 degrees C to 85 degrees C are obtained for CSP BST that thus outperforms conventionally sintered BST ceramics. Significant decrease in the sintering temperature and enhanced dielectric performance respond to the current sustainability concerns related to energy efficiency and tunable device requirements.

The vital issues of rechargeable lithium batteries widely used for everyday energy storage is being studied by many researchers to enhance the battery performance and safety. Graphene as well as cheaper and more accessible reduced graphene oxide (rGO) are known for high electrical conductivity, specific surface area and chemical stability. Providing thus high specific power and long cycle life, graphene and rGO in the form of porous frameworks like aerogels, foams, sponges (all denoted here as GA) have been successfully tested in electrodes of various types of lithium batteries. In this article, we review advances in synthesis and use of GA in high-performance electrode materials of lithium-ion (Li-ion), lithium-sulfur (LiS), and lithium-air (LiO2) batteries. Published results on the specific capacity of the lithium-battery electrodes using GA, the effect of GA on the cycling stability, and methods to enhance the performance of Li-ion, LiS and LiO2 batteries using porous microstructure of GA are overviewed and discussed. Thus, we provide an in-depth summary on diverse promising approaches of significant breakthroughs in recent years and present strategies to choose porous graphene frameworks for the sustainable lithium-battery electrodes.

Y2.80Pr0.20Fe5O12/Ba0.6Sr0.4TiO3 thin film heterostructure was claimed by Jiao et al. in Journal of Materials Science & Technology 202 (2024) 174 as a tunable dielectric material with superior performance achieved under simultaneous application of the electric and magnetic fields at a particular frequency of 1.44 MHz. However, here we express concerns regarding the real presence of the phenomenon at 1.44 MHz in the studied structures based on the literature and dielectric spectroscopy basics. We also note that the presented dielectric results and their interpretations are contradictory.

Ba(1-x)SrxTiO3 (BST) is a crucial dielectric material in tunable devices for modern wireless communication technologies, owing to high dielectric tunability and low dielectric loss. However, the conventional processing of BST ceramics requires a high sintering temperature of about 1350 degrees C. In this work, we demonstrate the feasibility of using Flash sintering (FS) and corresponding maps to process Ba0.6Sr0.4TiO3 ceramics, resulting in a 350 degrees C decrease in sintering temperature and 7 h reduction in sintering process time. The Flash-sintered BST exhibits a finer grain microstructure, lower dielectric loss, and significantly higher K-factor (figure of merit for tunability) when compared to conventionally sintered BST, unequivocally meeting the application criteria for tunable materials. Our findings highlight the effectiveness of FS as an alternative method for the rapid sintering of BST, while also opening up possibilities for further research into more efficient sintering processes for electroceramics.

In the context of sensor, actuator, and energy harvesting applications, lead-free ferroelectric K0.5Na0.5NbO3 (KNN) ceramics offer several advantages, including a high transition temperature and an elevated piezoelectric coefficient. However, producing single-phase KNN ceramics at a low thermal budget requires alternative sintering processes such as electric-field- and current-assisted flash sintering. Furthermore, the electrical properties of flash-sintered ferroelectrics are rarely disclosed. Here, based on systematic dielectric and ferroelectric, impedance spectroscopy and DC conductivity measurements, we demonstrate that the electrical performance of flash-sintered KNN is quite dependent on its thermal history, in contrast to the conventionally sintered one. Simultaneously, we demonstrate the successful production of high-performance KNN ceramics with high polarization, dielectric permittivity, Curie temperature, and piezoelectric coefficient using flash sintering, coupled with a carefully chosen post-sintering electrode curing step. Supported by impedance spectroscopy results, indicative of enhanced oxygen vacancy content in flash-sintered KNN, we postulate that post-sintering heat treatment and low-thermal-budget flash sintering are equally critical for KNN applications, complementing the benefits of reducing lattice defects and enhancing electroceramic performance. Our results demonstrate a pathway towards alternative sintering of electroceramics and offer opportunities to control performance. Electrical performance of flash-sintered K0.5Na0.5NbO3 ceramics: after annealing, both conventional and flash-sintered KNN ceramics exhibited electrically homogeneous behaviour similar to that of single crystals.

SrTi2O5 particles were claimed by Panda et al. in J. Materiomics 2023;9:609 as a new lead-free ferroelectric material with orthorhombic symmetry and space group of Cmm2, being, therefore, employed as a base of piezoelectric energy harvesters. However, in this comment we express concerns regarding the presence of the piezoelectricity in the studied material and the interpretation of the structural, microstructural, and ferroelectric results in that publication as those associated with SrTi2O5. We also note that the presented dielectric results are contradictory and that many important details are missing.

In a view of application of porous materials in wearable electronics and self-powered systems, reduced graphene oxide (rGO) foams modified by Mn or/and Bi were produced in this study to be used as electrodes for supercapacitors. The hydrothermal method and the freeze-drying processes were used for the preparation of the materials further morphologically, elementally and structurally analyzed. Based on the electrochemical characterization, Bi-modified rGO foam was found to be more a promising material for capacitive electrodes in comparison to the other prepared materials.

In a view of the research interest in the high-permittivity materials, continuous enhancement of the dielectric permittivity ε′ with Zn content was reported for conventionally prepared Sr1-xZnxTiO3 ceramics with x up to 0.009, limited by the solubility of Zn on Sr site. Here, we use a sol-gel technique and a relatively low annealing temperature of 750 °C to prepare monophasic Sr1-xZnxTiO3 thin films with higher x of 0.01, 0.05, and 0.10 on Pt/TiO2/SiO2/Si substrates. The incorporation of Zn on the Sr site is confirmed by the decrease of the lattice parameter, while the presence of Zn in the films is proven by energy dispersive spectroscopy. The film thickness is found to be ~330 nm by scanning electron microscopy, while the average grain size of 86–145 nm and roughness of 0.88–2.58 nm are defined using atomic force microscopy. ε′ measured on the films down to 10 K shows a decreasing trend with Zn content in contrast to that for weakly doped Sr1-xZnxTiO3 ceramics. At the same time, the temperature dependence of the dissipation factor tanδ reveals a peak, which intensity and temperature increase with Zn content.

Barium titanate (BT) nanoparticles were prepared using both microwave- and conventional oven-assisted hydrothermal syntheses with varying reaction times (1 h, 3 h, and 6 h). In the case of the conventional oven-assisted hydrothermal syntheses, 16 h, 24 h, 48 h and 72 h reaction times were also studied. Structural and morphological evolution of BT particles were investigated. Microwave-assisted hydrothermal synthesis allowed for the rapid formation of nearly pure barium titanate (BT) phase in just 1 h at 200 degrees C. On the other hand, using a conventional oven as the heat source required at least 6 h of synthesis to achieve a similar material. When the different BT powders were pelletized and sintered at 1300 degrees C, ceramics with over 95 % density were obtained. The room-temperature (RT) dielectric permittivity exceeded 1750 for BT particles prepared over 6 h using both heating methods. However, a significant distinction emerged when comparing the piezoelectric coefficient (d(33)) values. The BT pellet obtained through the sintering of BT synthesized in the conventional oven for 6 h exhibited a notably higher d(33) value, approximately 171 pC/N, as opposed to the 146 pC/N value observed in BT ceramics resulting from the microwave synthesized powders. Among the ceramic BT variations, the one derived from the best-crystallized tetragonal BT particles (CON_72h) displayed the lowest d(33) value at 79 pC/N. These findings underscore the immense potential of microwave- and conventional oven-assisted hydrothermal syntheses in the sustainable production of BT nanomaterials, which can then be sintered to enable the preparation of ceramics with enhanced ferroelectric and piezoelectric properties.

Ultrafast high-temperature sintering (UHS) is a rapidly growing research area of material science and engineering. Herein we present UHS of gadolinia-doped ceria (GDC) powders in single and multi-step approaches. The sintered ceramics were characterized from a physical and electrochemical point of view. When the power is applied gradually during the multistep UHS process crack-free GDC ceramics can be obtained with 95 % bulk density using commercial powder. Oxalate converted GDC powder gave 86 % bulk density with the same multistep sintering process. Additionally, it is shown that multistep UHS is also suitable for multilayer cosintering necessary for solid oxide fuel cells (SOFC), as demonstrated by the production of dense GDC electrolyte in tight contact with porous electrodes.

The energy demands of the mankind are exponentially rising and the worldwide research is focused on the clean and sustainable energy sources during the last years. As one of the possible ways to enable the transformation from a fossil fuel based to a low-carbon socio-economical epoch is the harvesting of unused heat in automotive exhaustion, industrial processes and home heating, etc. Thermoelectric (TE) generators can convert the heat to electrical energy thanks to Seebeck effect when electricity appears between cold and hot ends of usually semiconductor materials. To be interesting for potential commercial use in TE generators the materials need to be of high figure of merit (ZT), possessing high electrical conductivity and Seebeck coefficient together with low thermal conductivity. In addition to high-ZT chalcogenide- and skutterudite-type heavy-metal-based alloys, including rare-earth and expensive elements, metal oxide TE materials have advantages of low cost, environment friendly manufacturing and chemical stability at high temperatures. However, since they exhibit rather low electrical and high thermal conductivity compared to traditional TE materials, numerous studies have been done to optimise the TE oxide response by doping, nanostructuring, etc. Here, reports on most studied p- and n-type semiconductor metal oxides as well as the newest research on the enhancement of their TE performance by different methods are reviewed.