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KNbO3 single crystals are grown by the self-flux method using K2CO3 as a flux, but often suffer from discolouration. In this work, KNbO3 single crystals were grown by the flux method using KBO2 as a flux. KNbO3 powder was prepared by the solid-state reaction of K2CO3 and Nb2O5. KBO2 was fabricated by the reaction of K2B4O7·4H2O and K2CO3. Single crystals of KNbO3 were grown in a Pt crucible and the structure and dielectric properties of the single crystals were investigated. X-ray diffraction showed the KNbO3 single crystals to have an orthorhombic Cmm2 perovskite unit cell at room temperature. The existence of ferroelastic domains was revealed by transmission electron microscopy. Electron probe microanalysis showed the single crystals to be stoichiometric and contain small amounts of B. Differential thermal analysis, Raman scattering and impedance spectroscopy were used to study the phase transitions. KBO2 may be a suitable flux for the growth of KNbO3 single crystals. [ABSTRACT FROM AUTHOR]

The structural features and optical properties of supramolecular cyanoiron salts containing bis-pyridinium-4-oxime Toxogonin® (TOXO) as an electron acceptor are presented. The properties of the new TOXO-based cyanoiron materials were probed by employing two cyanoiron platforms: hexacyanoferrate(II), [Fe(CN)6]4– (HCF); and nitroprusside, [Fe(CN)5(NO)]2– (NP). Two water-insoluble inter-ionic donor–acceptor phases were characterized: the as-prepared microcrystalline reddish-brown (TOXO)2[Fe(CN)6]·8H2O (1a) with a medium-responsive, hydrochromic character; and the dark violet crystalline (TOXO)2[Fe(CN)6]·3.5H2O (1cr). Complex 1a, upon external stimulation, transforms to the violet anhydrous phase (TOXO)2[Fe(CN)6] (1b), which upon water uptake transforms back to 1a. Using the NP platform resulted in the water-insoluble crystalline salt TOXO[Fe(CN)5(NO)]·2H2O (2). The structures of 1cr and 2, solved by single-crystal X-ray diffraction, along with a comparative spectroscopic (UV–vis–NIR diffuse reflectance, IR, solid-state MAS-NMR, Mössbauer), thermal, powder X-ray diffraction, and microscopic analysis (SEM, TEM) of the isolated materials, provided insight for the supramolecular binding, electron-accepting, and H-bonding capabilities of TOXO in the self-assembly of these functionalized materials. [ABSTRACT FROM AUTHOR]

Amphibole asbestos is related to multiple diseases, mainly those targeting the lungs. Asbestos-related malignancies can also be caused by non-regulated asbestiform minerals and some elongated mineral particles (EMPs). In particular, the role of nano- and micro-sized EMPs internalized by lung epithelial cells must be clarified. This is of major importance when considering that EMPs to which humans are exposed are likely a highly heterogeneous mix of different mineral types, shapes, and sizes. Here, we document that particles smaller than 4.54 µm in length and smaller than 0.89 µm in width (e.g., particles that do not fit the regulatory categories to be identified as asbestos) are easily internalized because of their specific dimensions, surface charge, and shape (mostly dictated by the aspect ratio L/w). Once internalized, these particles can be found in proximity to the cell nucleus, in vesicles, and in the cytoplasm. Examining the localization of particles in cells provides important information, which helps in determining the physicochemical environment found inside the biological compartment, thus allowing for a better comprehension of the mineralogical transformation that might happen after internalization by cells. [ABSTRACT FROM AUTHOR]

In the search for electronic phenomena in high-entropy alloys (HEAs) that go beyond the independent-electron description, we have synthesized a series of hexagonal rare earth (RE)-based HEAs: CexLaLuScY (x = 0.05–1.0). The measurements of electrical resistivity, magnetic susceptibility and specific heat have shown that the CexLaLuScY HEAs exhibit the Kondo effect, which is of a single impurity type in the entire range of employed Ce concentrations despite the alloys being classified as dense (concentrated) Kondo systems. A comparison to other known dense Kondo systems has revealed that the Kondo effect in the CexLaLuScY HEAs behaves quite differently from the chemically ordered Kondo lattices but quite similar to the RE-containing magnetic metallic glasses and randomly chemically disordered Kondo lattices of the chemical formula RE1xRE21−xM (with RE1 being magnetic and RE2 being nonmagnetic). The main reason for the similarity between HEAs and the metallic glasses and chemically disordered Kondo lattices appears to be the absence of a periodic 4f sublattice in these systems, which prevents the formation of a coherent state between the 4f-scattering sites in the T → 0 limit. The crystal-glass duality of HEAs does not bring conceptually new features to the Kondo effect that would not be already present in other disordered dense Kondo systems. This study broadens the classification of HEAs to correlated electron systems. [ABSTRACT FROM AUTHOR]

In this study, we present a new approach for the synthesis of Pt/SnO2 catalysts using microwave radiation. Pt(IV) and Sn(IV) inorganic precursors (H2PtCl6 and SnCl4) and ammonia were used, which allowed the controlled formation of platinum particles on the anisotropic SnO2 support. The synthesized Pt/SnO2 samples are mesoporous and exhibit a reversible physisorption isotherm of type IV. The XRD patterns confirmed the presence of platinum maxima in all Pt/SnO2 samples. The Williamson-Hall diagram showed SnO2 anisotropy with crystallite sizes of ~10 nm along the c-axis (< 00l >) and ~5 nm along the a-axis (< h00 >). SEM analysis revealed anisotropic, urchin-like SnO2 particles. XPS results indicated relatively low average oxidation states of platinum, close to Pt metal. 119Sn Mössbauer spectroscopy indicated electronic interactions between Pt and SnO2 particles. The synthesized samples were used for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of excess NaBH4. The catalytic activity of the Pt/SnO2 samples for the reduction of 4-NP to 4-AP was optimized by varying the synthesis parameters and Pt loading. The optimal platinum loading for the reduction of 4-NP to 4-AP on the anisotropic SnO2 support is 5 mol% with an apparent rate constant k = 0.59 × 10–2 s–1. The Pt/SnO2 sample showed exceptional reusability and retained an efficiency of 81.4% after ten cycles. [ABSTRACT FROM AUTHOR]

The thermal treatment of electromechanically active thick films prepared by aerosol deposition (AD) is a common practice to improve their electrical and electromechanical properties. We report on how post-deposition annealing in air affects the unique cross-sectional microstructure and mechanical properties of 0.9Pb(Mg1/3Nb2/3)O3−0.1PbTiO3 thick films prepared by AD. Transmission electron microscopy revealed minor but detectable changes, such as pore redistribution and grain growth after annealing at 500 °C. We also showed that the stainless-steel substrate is strongly affected by the annealing. The hardness and Young's modulus of the films increased after annealing, with both properties being discussed in terms of their distribution over the cross-sections of the films. [ABSTRACT FROM AUTHOR]

Titanium oxynitride carbon composite nanofibers (TiON/C-CNFs) were synthesised with electrospinning and subsequent heat treatment in ammonia gas. In situ four-probe electrical conductivity measurements of individual TiON/C-CNFs were performed. Additionally, the TiON/C-CNFs were thoroughly analysed with various techniques, such as X-ray and electron diffractions, electron microscopies and spectroscopies, thermogravimetric analysis and chemical analysis to determine the crystal structure, morphology, chemical composition, and N/O at. ratio. It was found that nanofibers were composed of 2–5 nm sized titanium oxynitride (TiON) nanoparticles embedded in an amorphous carbon matrix with a small degree of porosity. The average electrical conductivity of a single TiON/C-CNF was 1.2 kS/m and the bulk electrical conductivity of the TiON/C-CNF fabric was 0.053 kS/m. From the available data, the mesh density of the TiON/C-CNF fabric was estimated to have a characteristic length of 1.0 µm and electrical conductivity of a single TiON/C-CNF was estimated to be from 0.45 kS/m to 19 kS/m. The electrical conductivity of the measured TiON/C-CNFs is better than that of amorphous carbon nanofibers and has ohmic behaviour, which indicates that it can effectively serve as a new type of support material for electrocatalysts, batteries, sensors or supercapacitors. [ABSTRACT FROM AUTHOR]

Spontaneous metallic Pb whisker formation from Pb and Bi containing Al-alloy's surfaces is a newly discovered phenomenon. The whiskers display unique formations, growth and morphology, which give the opportunity to be applied for specialized sensor and electronics applications. Within this work, the impact of environmental conditions (gas composition and moisture) is investigated and correlated with the modification of whisker evolution and growth dynamics. Furthermore, the residual stress state of the aluminum matrix using deep cryogenic treatment is modified and used to further increase whisker nucleation and growth by up to three- and seven-fold, respectively, supported by quantitative results. The results of this paper indicate the possibility to manipulate the whisker not only in terms of their kinetics but also their morphology (optimal conditions are 20% O2 and 35% humidity). Such features allow the tailoring of the whisker structure and surface to volume ratio, which can be optimized for different applications. Finally, this research provides new insight into the growth dynamics of the whiskers through in situ and ex situ measurements, providing further evidence of the complex nucleation and growth mechanisms that dictate the spontaneous growth of Pb whiskers from Al-alloy 6026 surfaces with growth velocities up to 1.15 µm/s. [ABSTRACT FROM AUTHOR]

The understanding of the origin of a two-dimensional electron gas (2DEG) at the surface of anatase TiO2 remains a challenging issue. In particular, in TiO2 ultra-thin films, it is extremely difficult to distinguish intrinsic effects, due to the physics of the TiO2, from extrinsic effects, such as those arising from structural defects, dislocations, and the presence of competing phases at the film/substrate interface. It is, therefore, mandatory to unambiguously ascertain the structure of the TiO2/substrate interface. In this work, by combining high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), density functional theory calculations, and multislice image simulations, we have investigated the nature of strainless anatase TiO2 thin films grown on LaAlO3 substrate. In particular, the presence of oxygen vacancies in anatase TiO2 has been proved to stabilize the formation of an extra alloy layer, Ti2AlO4, by means of interface rearrangement. Our results, therefore, elucidate why the growth of anatase TiO2 directly on LaAlO3 substrate has required the deposition of a TiOx extra-layer to have a 2DEG established, thus confirming the absence of a critical thickness for the TiO2 to stabilize a 2DEG at its surface. These findings provide fundamental insights on the underlying formation mechanism of the 2DEG in TiO2/LAO hetero-interfaces to engineer the 2DEG formation in anatase TiO2 for tailored applications. [ABSTRACT FROM AUTHOR]

Bacterial adhesion can be controlled by different material surface properties, such as surface charge, on which we concentrate in our study. We use a silica surface on which poly(allylamine hydrochloride)/sodium poly(4-styrenesulfonate) (PAH/PSS) polyelectrolyte multilayers were formed. The corresponding surface roughness and hydrophobicity were determined by atomic force microscopy and tensiometry. The surface charge was examined by the zeta potential measurements of silica particles covered with polyelectrolyte multilayers, whereby ionic strength and polyelectrolyte concentrations significantly influenced the build-up process. For adhesion experiments, we used the bacterium Pseudomonas aeruginosa. The extent of adhered bacteria on the surface was determined by scanning electron microscopy. The results showed that the extent of adhered bacteria mostly depends on the type of terminating polyelectrolyte layer, since relatively low differences in surface roughness and hydrophobicity were obtained. In the case of polyelectrolyte multilayers terminating with a positively charged layer, bacterial adhesion was more pronounced than in the case when the polyelectrolyte layer was negatively charged. [ABSTRACT FROM AUTHOR]

The dispersion of platinum (Pt) on metal oxide supports is important for catalytic and gas sensing applications. In this work, we used mechanochemical dispersion and compatible Fe(II) acetate, Sn(II) acetate and Pt(II) acetylacetonate powders to better disperse Pt in Fe2O3 and SnO2. The dispersion of platinum in SnO2 is significantly different from the dispersion of Pt over Fe2O3. Electron microscopy has shown that the elements Sn, O and Pt are homogeneously dispersed in α-SnO2 (cassiterite), indicating the formation of a (Pt,Sn)O2 solid solution. In contrast, platinum is dispersed in α-Fe2O3 (hematite) mainly in the form of isolated Pt nanoparticles despite the oxidative conditions during annealing. The size of the dispersed Pt nanoparticles over α-Fe2O3 can be controlled by changing the experimental conditions and is set to 2.2, 1.2 and 0.8 nm. The rather different Pt dispersion in α-SnO2 and α-Fe2O3 is due to the fact that Pt4+ can be stabilized in the α-SnO2 structure by replacing Sn4+ with Pt4+ in the crystal lattice, while the substitution of Fe3+ with Pt4+ is unfavorable and Pt4+ is mainly expelled from the lattice at the surface of α-Fe2O3 to form isolated platinum nanoparticles. [ABSTRACT FROM AUTHOR]

The structure–property relationship of catalytic supports for the deposition of redox-active transition metals is of great importance for improving the catalytic efficiency and reusability of the catalysts. In this work, the role of alumina support precursors of Cu-Fe/Al2O3 catalysts used for the total oxidation of toluene as a model volatile organic air pollutant is elucidated. Surface characterization of the catalysts revealed that the surface area, pore volume and acid site concentration of the alumina supports are important but not the determining factors for the catalytic activity of the studied catalysts for this type of reaction. The determining factors are the structural order of the support precursor, the homogeneous distribution of the catalytic sites and reducibility, which were elucidated by XRD, NMR, TEM and temperature programed reduction (TPR). Cu–Fe/Al2O3 prepared from bayerite and pseudoboehmite as highly ordered precursors showed better catalytic performance compared to Cu-Fe/Al2O3 derived from the amorphous alumina precursor and dawsonite. Homogeneous distribution of FexOy and CuOx with defined Cu/Fe molar ratio on the Al2O3 support is required for the efficient catalytic performance of the material. The study showed a beneficial effect of low iron concentration introduced into the alumina precursor during the alumina support synthesis procedure, which resulted in a homogeneous metal oxide distribution on the support. [ABSTRACT FROM AUTHOR]

This paper reports the results of an investigation of the oxidation of a sputter-deposited TiAlN hard coating in air at temperatures of 800 and 850 °C for times ranging from 15 min to 2 h. The study is focused on the role of growth defects in the oxidation process. The mechanism of oxidation at the site of the defect was studied on cross-sections made by the consecutive sectioning of oxidized coatings with the FIB technique. We found that in the early stage of oxidation, the locally intense oxidation always starts at such defects. Although the growth defects reduce the oxidation resistance of the coating locally, we believe that they do not have a decisive influence on the global oxidation resistance of the coating. There are several reasons for this. The first is that the surface area covered by growth defects is relatively low (less than 1%). Secondly, the coating is permeable only at those defects that extend through the entire coating thickness. Thirdly, the permeability at the rim of some defects strongly depends on the density of pores at the rim of defects and how open they are. The size and density of such pores depend on the shape and size of topographical irregularities on the substrate surface (e.g., seeds, pits), which are responsible for the formation of growth defects. We also found that oxidation of the TiAlN coating is accelerated by oxygen and titanium diffusion through the pores formed by crystal grain growth in the outer alumina overlayer. Such pores are formed due to the compressive stresses in the Ti-rich oxide layer, which are caused by the large difference in molar volumes between the oxide and nitride phases. [ABSTRACT FROM AUTHOR]

We present here important new findings on the direct synthesis of bimetal Cu-Mn containing porous silica catalyst and the effects of structure-directing agent removal from the prepared nanomaterial on the evolution of surface catalytic sites. The extraction-calcination procedure of the structure-directing agent removal led to the formation of Cu and Mn oxo-clusters and Cu and Mn oxide nanoparticles smaller than 5 nm, while the solely calcination procedure led to the mentioned species and in addition to the appearance of CuO nanoparticles 20 nm in size. Catalysts were tested in the Fenton-like catalytic degradation of dyes with different molecular charge (cationic, anionic, and zwitterionic) as model organic pollutants in wastewater at neutral pH. Significantly faster degradation of cationic and anionic dyes in the first 60 min was observed with the catalyst containing larger CuO nanoparticles (>20 nm) due to the less hindered generation of •OH radicals and slower obstructing of the active sites on the catalysts surface by intermediates. However, this was not found beneficial for zwitterionic dye with no adsorption on the catalysts surface, where the catalyst with smaller Cu species performed better. [ABSTRACT FROM AUTHOR]

Magnetic polymer gels are a new promising class of nanocomposite gels. In this work, magnetic PEO/iron oxide nanocomposite hydrogels were synthesized using the one-step γ-irradiation method starting from poly(ethylene oxide) (PEO) and iron(III) precursor alkaline aqueous suspensions followed by simultaneous crosslinking of PEO chains and reduction of Fe(III) precursor. γ-irradiation dose and concentrations of Fe3+, 2-propanol and PEO in the initial suspensions were varied and optimized. With 2-propanol and at high doses magnetic gels with embedded magnetite nanoparticles were obtained, as confirmed by XRD, SEM and Mössbauer spectrometry. The quantitative determination of γ-irradiation generated Fe2+ was performed using the 1,10-phenanthroline method. The maximal Fe2+ molar fraction of 0.55 was achieved at 300 kGy, pH = 12 and initial 5% of Fe3+. The DSC and rheological measurements confirmed the formation of a well-structured network. The thermal and rheological properties of gels depended on the dose, PEO concentration and initial Fe3+ content (amount of nanoparticles synthesized inside gels). More amorphous and stronger gels were formed at higher dose and higher nanoparticle content. The properties of synthesized gels were determined by the presence of magnetic iron oxide nanoparticles, which acted as reinforcing agents and additional crosslinkers of PEO chains thus facilitating the one-step gel formation. [ABSTRACT FROM AUTHOR]

Self-supporting thin films containing nanopores are very promising materials for use for multiple applications, especially in nanofiltration. Here, we present a method for the production of nanomembranes containing a 3D ordered network of nanopores in an alumina matrix, with a diameter of about 1 nm and a body centered tetragonal structure of the network nodes. The material is produced by the magnetron sputtering deposition of a 3D ordered network of Ge nanowires in an alumina matrix, followed by a specific annealing process resulting in the evaporation of Ge. We demonstrate that the films can be easily grown on commercially available alumina substrates containing larger pores with diameters between 20 and 400 nm. We have determined the minimal film thickness needed to entirely cover the larger pores. We believe that these films have the potential for applications in the fields of filtration, separation and sensing. [ABSTRACT FROM AUTHOR]

Recently demonstrated 3D networks of Ge quantum wires in an alumina matrix, produced by a simple magnetron sputtering deposition enables the realization of nanodevices with tailored conductivity and opto-electrical properties. Their growth and ordering mechanisms as well as possibilities in the design of their structure have not been explored yet. Here, we investigate a broad range of deposition conditions leading to the formation of such quantum wire networks. The resulting structures show an extraordinary tenability of the networks' geometrical properties. These properties are easily controllable by deposition temperature and Ge concentration. The network's geometry is shown to retain the same basic structure, adjusting its parameters according to Ge concentration in the material. In addition, the networks' growth and ordering mechanisms are explained. Furthermore, optical measurements demonstrate that the presented networks show strong confinement effects controllable by their geometrical parameters. Interestingly, energy shift is the largest for the longest quantum wires, and quantum wire length is the main parameter for control of confinement. Presented results demonstrate a method to produce unique materials with designable properties by a simple self-assembled growth method and reveal a self-assembling growth mechanism of novel 3D ordered Ge nanostructures with highly designable optical properties. [ABSTRACT FROM AUTHOR]

We report on a heterogeneity study, down to the atomic scale, on a representative multiple-element-modified ceramic based on potassium sodium niobate (KNN): 0.95(Na0.49K0.49Li0.02)(Nb0.8Ta0.2)O3–0.05CaZrO3 with 2 wt % MnO2. We show that different routes for incorporating the MnO2 (either before or after the calcination step) affect the phase composition and finally the functionality of the material. According to X-ray diffraction and scanning electron microscopy analyses, the ceramics consist of orthorhombic and tetragonal perovskite phases together with a small amount of Mn-rich secondary phase. The addition of MnO2 after the calcination results in better piezoelectric properties, corresponding to a ratio between the orthorhombic and tetragonal perovskite phases that is closer to unity. We also show, using microscopy techniques combined with analytical tools, that Zr-rich, Ta-rich and Mn-rich segregations are present on the nano and atomic levels. With this multi-scale analysis approach, we demonstrate that the functional properties are sensitive to minor modifications in the synthesis route, and consequently to different material properties on all scales. We believe that detecting and learning how to control these modifications will be a step forward in overcoming the irreproducibility problems with KNN-based materials. [ABSTRACT FROM AUTHOR]

Iron-functionalized disordered mesoporous silica (FeKIL-2) is a promising, environmentally friendly, cost-effective and highly efficient catalyst for the elimination of volatile organic compounds (VOCs) from polluted air via catalytic oxidation. In this study, we investigated the type of catalytically active iron sites for different iron concentrations in FeKIL-2 catalysts using advanced characterization of the local environment of iron atoms by a combination of X-ray Absorption Spectroscopy Techniques (XANES, EXAFS) and Atomic-Resolution Scanning Transmission Electron Microscopy (AR STEM). We found that the molar ratio Fe/Si ≤ 0.01 leads to the formation of stable, mostly isolated Fe 3+ sites in the silica matrix, while higher iron content Fe/Si > 0.01 leads to the formation of oligonuclear iron clusters. STEM imaging and EELS techniques confirmed the existence of these clusters. Their size ranges from one to a few nanometers, and they are unevenly distributed throughout the material. The size of the clusters was also found to be similar, regardless of the nominal concentration of iron (Fe/Si = 0.02 and Fe/Si = 0.05). From the results obtained from sample characterization and model catalytic tests, we established that the enhanced activity of FeKIL-2 with the optimal Fe/Si = 0.01 ratio can be attributed to: (1) the optimal concentration of stable isolated Fe 3+ in the silica support; and (2) accelerated diffusion of the reactants in disordered mesoporous silica (FeKIL-2) when compared to ordered mesoporous silica materials (FeSBA-15, FeMCM-41).