This study considered and compared silver, gold, and their combination of nanoparticles (AgNPs, AuNPs, and Au-AgNPs) with biocompatible material mesoporous silica SBA-15 as potential antibacterial agents. A facile, one-pot “green” methodology, utilizing L-histidine as a reducing agent and bridge between components, was employed to obtain Ag@SBA-15, Au@SBA-15, and Au-Ag@SBA-15 nanocomposites without the use of external additives. Various physicochemical tools (UV-Vis, TEM, SAED, FESEM, XPS, BET, XRD, and FTIR) presented SBA-15 as a good carrier for spherical AgNPs, AuNPs, and Au-AgNPs with average diameters of 8.5, 16, and 9 nm, respectively. Antibacterial evaluations of Escherichia coli and Staphylococcus aureus showed that only Ag@SBA-15, at a very low Ag concentration (1 ppm) during 2 h of contact, completely reduced the growth (99.99%) of both strains, while the Au@SBA-15 nanocomposite required higher concentrations (5 ppm) and time (4 h) to reduce 99.98% E. coli and 94.54% S. aureus. However, Au introduction in Ag@SBA-15 to form Au-Ag@SBA-15 negatively affected its antibacterial potential, lowering it due to the galvanic replacement reaction. Nevertheless, the rapid and effective combating of two bacteria at low NPs concentrations, through the synergistic effects of mesoporous silica and AgNPs or AuNPs, in Ag@SBA-15 and Au@SBA-15 nanocomposites, provides a potential substitute for existing bacterial disinfectants.

Cold sintering of perovskite materials is still, despite years of research, challenging. The key objective when coldsintering oxide materials is finding an appropriate liquid phase that triggers pressure-dissolution process and mechano-chemical compaction and densification of ceramics. In this study, cold sintering of the multiferroic BiFeO3 perovskite is reported for the first time. When organic additives or solvents are used, these effectively sinter the compound, but cause precipitation of secondary phases that impede grain-to-grain contacts and the polarization coupling, and result in electrically conductive samples. We found that it is critical to carefully select the sintering additives based on their reactivity, decomposition temperature and products, while ensuring a significant level of wettability and matrix solubility. NaOH/KOH mixture was found to be the best sintering aid, resulting in remanent polarization and strain responses of cold-sintered BFO comparable to those reported for conventionally sintered ceramics.

To date, no piezoelectric material system has been developed that would match the piezoelectric performance of the group of lead-based relaxor ferroelectrics, such as Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT). In the quest to find alternatives, continuous efforts have been made to understand the complex microscopic origins leading to the large macroscopic piezoelectric response of PMN-PT and similar lead-based perovskites with relaxor characteristics. Despite significant advances, it is still unclear whether those concepts can be efficiently used to develop lead-free relaxor ferroelectric alternatives. Here, a large piezoelectric response of BiFeO3-BaTiO3 (BFO-BTO) ceramics is reported, characterized by a d33 coefficient of 1200 pm V-1 measured at 325 degrees C, 1 kV cm-1 of driving field and 90 Hz of field frequency. While composed of multiple contributions, the large response is found to be dominated by a strongly nonlinear and hysteretic process, likely associated with the dynamics of hierarchically arranged nanodomain walls, thus resembling the mechanisms operating in lead-based relaxor materials. Although the response is triggered upon elevated thermal energy, the results provide valuable information about the microscopic behavior that can be potentially used to tailor the response of lead-free relaxor ferroelectrics and bring them closer to the highly performant lead-based perovskites.

The cosintering of particulate composites often presents a challenge due to the conventionally high processing temperatures used. Inter-diffusion of species between two phases and their volatilization, formation of secondary phases, and cracking or delamination of ceramics are effects that hinder the coupling of functional properties and reduce the final responses of such composites. This is particularly relevant when producing perovskite-perovskite composites from phases that are conventionally sintered at different temperatures (Ts), such as K 0.5 Na 0.5 NbO 3 (KNN; Ts=1100 degrees C) and BiFeO3 3 (BFO; Ts=800 degrees C). Obtaining high-quality KNN-BFO multifunctional composite was the goal of this study. We demonstrate herein that the low-temperature sintering technique known as the Cold Sintering Process (CSP) can be utilized for producing particulate perovskite-perovskite composites, specifically KNN-BFO. We show that cold-sintered KNN-BFO composites have a dense microstructure, good phase-to-phase contact, are crack- free and exhibit ferroelectric properties. Their dielectric and ferroelectric properties are strongly affected by the fraction of KNN, increasing polarization saturation, while BFO aids in increasing their dielectric breakdown strength.

The recent discovery of the large piezoelectric response of Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) ceramics induced by samarium doping has provided a substantially improved functionality to the group of lead-based relaxor-ferroelectric materials. Different mechanisms have been so far proposed for the large piezoelectricity; however, the explanations are contradictory and focused on a unified description. Here, we use nonlinear harmonic piezoelectric measurements combined with multiscale structural analysis to clarify the origins of the ultrahigh piezoelectric response of samarium-doped PMN-PT. Our methodological approach allowed us to separate the multiple piezoelectric contributions, revealing their quantitative role in the total response. The results show that the ultrahigh piezoelectricity cannot be attributed to a single mechanism but is rather a complex combination of different contributions originating from the multiple effects of samarium doping on the long- and short-range structure of PMN-PT. The study offers a baseline for future engineering of the key material parameters affecting the large piezoelectric response of relaxor-ferroelectric ceramics.

Because of their intrinsic polarization and related properties, ferroelectrics attract significant attention to address energy transformation and environmental protection. Here, by using trivalent-ion-lanthanum doping of BiFeO3 nanoparticles (NPs), it is shown that defects and piezoelectric potential are synergized to achieve a high piezocatalytic effect for decomposing the model Rhodamine B (RhB) pollutant, reaching a record-high piezocatalytic rate of 21 360 L mol-1 min-1 (i.e., 100% RhB degradation within 20 min) that exceeds most state-of-the art ferroelectrics. The piezocatalytic Bi0.99La0.01FeO3 NPs are also demonstrated to be versatile toward various pharmaceutical pollutants with over 90% removal efficiency, making them extremely efficient piezocatalysts for water purification. It is also shown that 1% La-doping introduces oxygen vacancies and Fe2+ defects. It is thus suggested that oxygen vacancies act as both active sites and charge providers, permitting more surface adsorption sites for the piezocatalysis process, and additional charges and better energy transfer between the NPs and surrounding molecules. Furthermore, the oxygen vacancies are proposed to couple to Fe2+ to form defect dipoles, which in turn introduces an internal field, resulting in more efficient charge de-trapping and separation when added to the piezopotential. This synergistic mechanism is believed to provide a new perspective for designing future piezocatalysts with high performance.

A novel and effective antibacterial agent based on a combination of copper nanoparticles (CuNPs) and polypyrrole (PPy) is presented. By using a straightforward in situ polymerization method in water, a copper/polypyrrole (Cu/PPy) nanocomposite with spherical CuNPs, around 25 nm in diameter, uniformly dispersed throughout a granular PPy matrix, was characterized and subjected to determination of antibacterial activity toward E. coli, and S. aureus. In this survey, the synergistic engagement of various features of CuNPs and PPy against bacteria was somewhat expected. After a 24 h interaction with S. aureus, already 2 ppm of Cu/PPy with only 9.45 wt% content of Cu is acting almost completely cidal, with 99.17 % bacterial growth inhibition, while 10 ppm has a cidal value of 99.99 % at the same time. Safe and environmentally acceptable concentrations of Cu/PPy indicate that it is convenient as an antibacterial agent for wider use.

Cold sintering is an attractive method for sintering ferroelectric ceramics at temperatures at or below 300 degrees C. While we can practically obtain bulk samples by introducing a transient liquid and applied pressure, the mechanisms of sintering and final functional properties of cold-sintered ceramics are far from being understood. Here, we investigate the influence of grain size and sintering parameters on the microstructure and ferroelectric properties of 0.5 % Sr-doped K0.5Na0.5NbO3 ceramics. By comparing with the conventionally-sintered samples, we find that cold-sintered ceramics have higher dielectric permittivity and lower dielectric losses, which we attribute to smaller grains and higher relative density. Using atomic-scale analysis, we point out the presence of numerous lattice dislocations that likely act as pinning sites and thus inhibit any significant polarizationswitching behaviour. Due to the slim P-E loop and high dielectric breakdown fields of the cold-sintered ceramics we consider its potential for energy storage applications.

The interaction of domain structure and defects in ferroelectric thin films has been studied for decades. However, the role of dislocations and thermal stability of microstructures is still poorly studied. By combining transmission electron microscopy, x-ray diffraction experiments, and phase-field simulations, we show that dislocation pairs induced by post-annealing above 550 °C provide a stress field stabilizing a domains in 30 nm thick tetragonal PbTiO3 films on SrTiO3 substrate, initially exhibiting pure c domains. Based on phase-field simulations, we further discuss the effects of single dislocations and dislocation pairs on the nucleation of a-domains and the occurrence of non-ferroelastic 180° domains. Dislocations, and the possibility to tune them using an appropriate thermal annealing process, offer a path for modulating the domains and domain wall states and, thus, the physical properties of ferroelectric films.

The archetypical antiferroelectric, PbZrO3, is currently attracting a lot of interest, but no consensus can be clearly established on the nature of its ground state as well as on the influence of external stimuli over its physical properties. Here, the antiferroelectric state of 45-nm-thick epitaxial thin films of PbZrO3 is established by observing the characteristic structural periodicity of antiparallel dipoles at the atomic scale, combined with clear double hysteresis of the polarization-electric field response related to antiferroelectric–to–ferroelectric phase transitions. Surprisingly, while the antiferroelectric state is identified as the ground state, temperature-dependent measurements show that a transition to a ferroelectric-like state appears in a large temperature window (100 K). Atomistic simulations further confirm the existence, and provides the origin, of such ferroelectric state in the films. Electric-field-induced ferroelectric transitions are also detected by the divergence of the piezoresponse force microscopy response. Using this technique, we further reveal the signature of a ferroelectric ground state for 4-nm-thick PbZrO3 films. Compared with bulk crystals, these results suggest a more complex competition between ferroelectric and antiferroelectric phases in epitaxial thin films of PbZrO3.

Multiferroic materials have attracted significant research attention due to their technological potential for applications as multifunctional devices. The scarcity of single-phase multiferroics and their low inherent coupling between multiferroic order parameters above room temperature pose a challenge to their further applications. We propose a 3BiFeO3/7BaTiO3 perovskite–perovskite composite that combines ferroelectricity and ferromagnetism. We demonstrate that the sintering temperature can tailor the ferroelectricity and ferromagnetism of the composites. The multiferroicity can be achieved at a low sintering temperature in the composite-like structure ceramics, and its multiferroic properties, especially the ferromagnetism, are superior to those of solid solutions. We also investigate the dynamic evolution of multiferroicity with sintering temperature. We adopt a nano–micro strategy to construct a composite-like microstructure, which results in optimized ferroelectric (1.62 μC cm−2) and ferromagnetic (0.16 emu/g) characteristics at a sintering temperature of 750 °C. We also found experimental evidence of the competition between antiferromagnetic and ferromagnetic interactions in the transition metal cation sublattice. Multiferroic BiFeO3/BaTiO3 composites with combined ferroelectric and ferromagnetic properties have significant potential for various applications.

Recently, piezoelectric‐based catalysis has been demonstrated to be an efficient means and promising alternative to sunlight‐driven photocatalysis, where mechanical vibrations trigger redox reactions. Here, 60 nm‐size BiFeO3 nanoparticles are shown to be very effective for piezo‐degrading Rhodamine B (RhB) model dye with record degradation rate reaching 13 810 L mol−1 min−1, and even 41 750 L mol−1 min−1 (i.e., 100% RhB degradation within 5 min) when piezocatalysis is synergistically combined with sunlight photocatalysis. These BiFeO3 piezocatalytic nanoparticles are also demonstrated to be versatile toward several dyes and pharmaceutical pollutants, with over 80% piezo‐decomposition within 120 min. The maintained high piezoelectric coefficient combined with low dielectric constant, high‐elastic modulus, and the nanosized shape make these BiFeO3 nanoparticles extremely efficient piezocatalysts. To avoid subsequent secondary pollution and enable their reusability, the BiFeO3 nanoparticles are further embedded in a polymer P(VDF‐TrFE) matrix. The as‐designed flexible, chemically stable, and recyclable nanocomposites still keep remarkable piezocatalytic and piezo‐photocatalytic performances (i.e., 92% and 100% RhB degradation, respectively, within 20 min). This work opens a new research avenue for BiFeO3 that is the model multiferroic and offers a new platform for water cleaning, as well as other applications such as water splitting, CO2 reduction, or surface purification.

The main limitations of current methods for synthesizing perovskite oxide (ABO3 ) nanoparticles (NPs), e.g., the high reagent costs and sophisticated equipment, the long time and high-temperature processing, or multiple post-processing and thermal treatment steps, hamper their full study and potential application. Here, we use a facile low temperature (50 °C) chemical bath synthesis and only one annealing step to successfully produce high phase purity and crystalline quality nano-shaped rare-earth-based REMO3 NPs (RE=La, Nd, Sm, Gd; M=Fe, Mn, Al). We also show the versatility of this approach by fabricating La0.7 Sr0.3 MnO3 solid solution and non-RE-based BiFeO3 perovskite. To assess the potential of the as-prepared REFeO3 and REMnO3 NPs, they are used for photocatalytic degradation of the norfloxacin antibiotic and show high efficiency. We believe this easy, robust, versatile, and general route for synthesizing ABO3 -based NPs can be further explored in the vast perovskite family and beyond.

Magnetoelectric multiferroics are provoking much research activity for their potential applications in novel multifunctional devices. Compared with single-phase multiferroics, magnetoelectric composites have competitive advantages. The magnetoelectric coupling of composites is heavily influenced by composition and grain size. We prepared BFO/PZT composites with separate phases via the solid-state sintering method. We show that equal molar ratio composition has a better magnetoelectric coupling response than other compositions. The composites with nano bismuth ferrite have better magnetoelectric coupling performance, and these with both nano grain sizes present the highest magnetoelectric voltage coefficients (<< E = 16.9 mV cm-1 Oe-1). The strain-mediated mechanism was confirmed via a comparison between strain response and polarization of nano/micro type composites with the composition of 3:7. We found that the magnetoelectric voltage coefficient << E positively correlates with strain response instead of polarization in BFO/PZT composites, which provides experimental evidence for the strain-mediated ME composite theory.(c) 2023 Published by Elsevier B.V.

The catalytic activity of five silver-polyaniline-polyvinylpyrrolidone (Ag@PANI@PVP1-5) nanocomposites for borohydride oxidation reaction (BOR) was thoroughly examined. The nanocomposites were synthesized by an in situ chemical oxidative polymerization of aniline monomer by Ag+ ions in the presence of accelerator - PVP and physicochemical properties were determined prior their use in electrocatalysis. Ag@PANI@PVP3 with 35.4 wt% Ag delivered the highest current density and specific current density during BOR. Evaluation of the order of reaction < 1 suggested indirect BOR mechanism. Furthermore, Ag@PANI@PVP3 also delivered the highest current density and stable performance during chronoamperometric study of BOR. Its apparent activation energy of 15 kJ mol-1 was found to be the lowest among the studied materials accounting for the high current densities.

BiFeO3 is the model multiferroic material widely considered as nanoparticles for its potential photocatalytic activity. In this work, we study the influence of annealing temperature on the structural, morphological and optical properties of BiFeO3 nanoparticles prepared by a facile chemical route and, the resulting photodegradation of Eosin B dye. When annealing temperature as low as 600 °C is used, some parasitic phases such as Bi2Fe4O9 appear in addition to the BiFeO3 phase. At the same time, the energy of the absorption onset and band gap shifts down and the photocatalytic activity toward Eosin B dye significantly increases by ∼27% when UV light is used while only a small if any, enhancement is observed in case of sunlight illumination. This photocatalytic enhancement could be therefore essentially attributed to the presence of secondary parasitic phases that could also explain previous reported observations. Furthermore, annealing at 500 °C to obtain pure parasitic-phase-free BiFeO3 nanopowder reveals excellent photodegradation of Eosin B reaching 95% efficiency after 40 min under sunlight illumination with good photostability after three consecutive degradation cycles.