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Ceramics based on calcium and sodium cobaltates are promising high-temperature thermoelectric oxide materials with complementary advantages. Ca3Co4O9 is stable at high temperatures, whereas Na0.75CoO2 can be easily processed as a textured ceramic with excellent thermoelectric properties. Na0.75CoO2, however, lacks long-term stability and degrades in even a relatively mild humid environment. In this work, we present a novel approach to the synthesis of complex composite materials based on intergrowths of sodium and calcium cobaltates that have excellent thermoelectric performance and improved stability. We synthesized samples with the mixed composition (3-x)Ca3Co4O9–4x(Na0.75CoO2) in an over-pressured oxygen atmosphere. Samples with the mixed Ca–Na composition developed textured microstructures composed of intergrowths of both end-members, as revealed by transmission electron microscopy. We also examined the thermoelectric performance of the investigated materials after exposure to high humidity and found that the composition with x = 0.8 (Ca:Na = 2.75) has long-term stability.

Epitaxial integration of transition-metal oxides with silicon brings a variety of functional properties to the well-established platform of electronic components. In this process, deoxidation and passivation of the silicon surface are one of the most important steps, which in our study were controlled by an ultra-thin layer of SrO and monitored by using transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), synchrotron X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED) methods. Results revealed that an insufficient amount of SrO leads to uneven deoxidation of the silicon surface i.e. formation of pits and islands, whereas the composition of the as-formed heterostructure gradually changes from strontium silicide at the interface with silicon, to strontium silicate and SrO in the topmost layer. Epitaxial ordering of SrO, occurring simultaneously with silicon deoxidation, was observed. RHEED analysis has identified that SrO is epitaxially aligned with the (001) Si substrate both with SrO (001) and SrO (111) out-of-plane directions. This observation was discussed from the point of view of SrO desorption, SrO-induced deoxidation of the Si (001) surface and other interfacial reactions as well as structural ordering of deposited SrO. Results of the study present an important milestone in understanding subsequent epitaxial integration of functional oxides with silicon using SrO. This journal is

Phase pure NaNb1−xTaxO3 ceramics have been successfully prepared by spark plasma sintering (SPS) process at 950–1150 °C. The structural evolution, dielectric and energy storage properties as a function of Ta-doping level were studied by X-ray diffraction (XRD) Rietveld refinement, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, scan electron microscopy (SEM) and ferroelectric analyzer. It was found that small level of Ta-doping induced the stabilization of ferroelectric phase from antiferroelectric NaNbO3, while high level of doping induced further transition from ferroelectric to paraelectric phase. The doping of Ta led to the decrease in Tc and dielectric loss. The NTN4 and NTN6 composition exhibited enhanced dielectric response due to the coexistence of ferroelectric/antiferroelectric or paraelectric phases. The presence of oxygen vacancies in the sintered body were confirmed, which gave rise to the loss at high temperature. The doping of Ta decreased the concentration of oxygen vacancies. Maximum energy density of ∼0.9 J/cm3 could be obtained for x = 0.6 composition with the BDS of ∼160 kV/cm and efficiency of ∼87%.

Nanotextured magnesium oxide (MgO) can exhibit both antibacterial and tissue regeneration activity, which makes it very useful for implant protection. To successfully combine these two properties, MgO needs to be processed within an appropriate carrier system that can keep MgO surface available for interactions with cells, slow down the conversion of MgO to the less active hydroxide and control MgO solubility. Here we present new composites with nanotextured MgO microrods embedded in different biodegradable polymer matrixes: poly-lactide-co-glycolide (PLGA), poly-lactide (PLA) and polycaprolactone (PCL). Relative to their hydrophilicity, polarity and degradability, the matrices were able to affect and control the structural and functional properties of the resulting composites in different manners. We found PLGA matrix the most effective in performing this task. The application of the nanotextured 1D morphology and the appropriate balancing of MgO/PLGA interphase interactions with optimal polymer degradation kinetics resulted in superior bactericidal activity of the composites against either planktonic E. coli or sessile S. epidermidis, S. aureus (multidrug resistant-MRSA) and three clinical strains isolated from implant-associated infections (S. aureus, E. coli and P. aeruginosa), while ensuring controllable release of magnesium ions and showing no harmful effects on red blood cells.

Because of the abounded presence of the silver-containing products in the market and intensively studied silver-containing biomaterials in the literature, we investigated a hypothesis that stabilizing silver within bioactive hydroxyapatite composite is capable to provide safe and effective antibacterial action. For that purpose nanocomposite made of bioactive, mineral hydroxyapatite (HAp) and antibacterial silver (Ag) is studied for interactions with both, bacterial and human cells. The nanocomposite provides controlled release of Ag ions; induces severe damages in bacterial cells and is capable for strong bacteriostatic and bactericidal action. On the other hand, investigations of the material's interactions with human cells confirm that lower concentrations are highly compatible with osteosarcoma and fetal lung fibroblasts, but at higher concentrations (that provide bacteriostatic and bactericidal influences in bacteria) the material is toxic and capable of inducing morphological changes similar to those observed in bacterial cells.

Pulsed-laser deposition was used to prepare Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) thin films on (LaNiO3)/SrTiO3 substrates. We found that the bottom electrode has an immense influence on the properties of the overgrown active layer. Specifically, we found that the use of LaNiO3 (LNO) as the electrode material strongly stabilizes the perovskite phase and significantly expands the process window for the preparation of phase-pure PMN-PT as compared to a direct deposition on SrTiO3 (STO) substrates. Based on our experiments, the stabilization is achieved primarily due to the increased interface roughness, which enhances the sticking of Pb-based species, thereby suppressing the formation of undesired Pb-deficient pyrochlore inclusions. The roughness of the interface does not have adverse effects on the quality of the films. In fact, the film prepared on the LNO/STO template from the Pb-rich target exhibited superior electrical properties as compared to the film prepared directly on STO. By understanding the mechanism, we were able to exploit it and prepare an STO/Nb:STO template with a rough surface, which strongly enhanced the stability of the perovskite phase. This approach can be used to design templates for different device configurations.

ABO 3 -type perovskite crystallites with symmetrical crystal structures do not show a tendency to grow in the shape of rods and plates, which are of great scientific interest due to their anisotropic physical properties. A topochemical transformation is one of the most convenient approaches for the preparation of such defined-shape perovskite particles, the functional properties of which can be additionally tailored by the formation of solid solutions. In this study a one-step topochemical conversion reaction from a Bi 4 Ti 3 O 12 template to A-site-substituted complex Ba 1-x Sr x TiO 3 perovskite microplates was investigated in order to understand the mechanism and to determine the compositional, structural and morphological correlations between the template and the final plate-like particles. Based on our finding that Sr incorporates in a 2.7-times larger amount than expected from the initial Ba/Sr ratio (0 1-x Sr x TiO 3 solid-solution composition could be prepared using this topochemical transformation. The tetragonal distortion of the Ba 1-x Sr x TiO 3 plates, expressed as the c/a ratio, was found to decrease linearly from 1.0092 (x = 0) to 1.0037 (x = 0.23), while the compositions with higher x were cubic (c/a=1). According to a piezo-response force microscope (PFM) examination, Ba 1-x Sr x TiO 3 plates with 0 ≤x ≤ 0.175 showed ferroelectric and piezoelectric characteristics. The temperature of the ferroelectric-to-paraelectric phase transition, as determined by differential scanning calorimetry (DSC), linearly decreased from 124 °C (x = 0) to 88 °C (x = 0.11). XRD examinations revealed a strong (001) preferential orientation for the plates (0 ≤ x ≤ 0.11) and the typical (001)/(100) peak splitting indicated the presence of c - and a -domains. The successful preparation and design of Ba 1-x Sr x TiO 3 plates increase the potential of this topochemical transformation for the preparation of plates with a variety of solid-solution compositions and controlled characteristics.

Made available in DSpace on 2018-12-11T17:21:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-12-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The formation of oxygen-related lattice defects and their influence on optical and electronic properties in CaCu3Ti4O12 (CCTO) ceramics were studied by controlling the oxygen partial pressure during the sintering process at high temperatures. The samples were analyzed using complementary bulk spectroscopic techniques such as photoluminescence spectroscopy, ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, and electron paramagnetic resonance. Our comprehensive study shows that the oxygen content during sintering process exerts considerable control over the type and concentration of oxygen-related defects in the crystalline CCTO structure. Our results also suggest that the formation of different types of oxygen-related defects in the structure modifies electronic energy levels and thus directly affects the electronic and optical properties of the CCTO phase. These results provided further insight into the important role of oxygen in the crystalline defect arrangement in polycrystalline CCTO ceramics. Physical Chemistry Department Chemistry Institute São Paulo State University (UNESP) Advanced Materials Department Jozef Stefan Institute Physical Chemistry Department Chemistry Institute São Paulo State University (UNESP) FAPESP: 09/00367-6 FAPESP: 13/07296-2 FAPESP: 13/14647-6 CNPq: 165902/2015-9 CNPq: 2012/51195-3 CNPq: 443138/2016-8

Growth of Pb(Mg 1/3 Nb 2/3 )O 3 –33PbTiO 3 thin films by pulsed-laser deposition directly on non-conductive SrTiO 3 substrates for d 33 -mode energy harvesters (EHs) was studied, as they offer a higher figure-of-merit than d 31 -mode EHs. It was found that a high defect density, present in the film grown at 0.13 mbar, is manifested in the form of splitting of the (00 l ) peaks in X-ray diffraction, which was avoided by raising the process pressure to 0.27 mbar. Nevertheless, both films grow in a combined 2D and 3D manner, and form out-of-phase boundaries (OPBs) with a PbO rock-salt structure between the as-grown islands. It was found that the overall composition of the sample with optimized structural and functional properties was Pb 1.07 Mg 0.19 Nb 0.44 Ti 0.32 O 3 , which is close to stoichiometric. The surplus of Pb is compensated by the formation of OPBs and Mg deficit maintains macroscopic electroneutrality. In-plane and out-of-plane relative permittivities of 1900 and 980, respectively, imply macroscopic out-of-plane polarization.

The integration of complex oxides with silicon represents a challenging task in materials science today, given the thermodynamic, chemical and structural incompatibilities between silicon and most of these complex oxides. A great amount of the research in this field has been done with samples grown by Molecular Beam Epitaxy (MBE), but the Pulsed Laser Deposition (PLD) technique offers several key advantages, and an easier scalability in industrial environments. In this work, we present a novel PLD-only procedure for the growth of ultra-thin and epitaxial SrTiO3 (STO) pseudo-templates on Si (0 0 1) surfaces. The careful control and optimization of critical growth parameters allow us to obtain samples with optimal Sr/Ti ratios, ultra-thin (1–2 nm) interfaces, and outstanding surface crystallinity. The validity of these pseudo-templates is also demonstrated by the overgrowth of STO thicker samples, which present interfaces and properties comparable to those of the pseudo-templates.

This paper presents the extraction of microwave properties of low-temperature cured inorganic composite materials based on barium titanate (BaTiO3). These composite materials exhibit attractive features such that when the volume fraction of the filler contents varied, its electrical properties of high permittivity and moderately low loss tangent can be manipulated to suit different areas of applications. For the extraction of the permittivity and the loss tangent, three different ink particles were developed and printed on the top of interdigital-shaped microwave capacitor. The properties of the inks were extracted from measured results through computer simulations. The obtained results were verified with several types of interdigital capacitor structures of different fingers and linewidths. The effect of the thickness of the ink layer materials on the top of the capacitor structures was likewise investigated. The results show relative permittivity ( $\varepsilon _{r}$ ) values of 30, 25, and 27 for composite layers printed using inks with Pr. A shape at 67.4 wt% (percentage by weight), Pr. B shape at 66.3 wt%, and Pr. C shape at 67.1 wt% of BaTiO3, respectively, at 2 GHz. Corresponding loss tangents (tan $\delta $ ) were 0.065, 0.040, and 0.025. The dielectric properties of the composite materials are influenced by the thickness variation of the ink layers on the capacitor structures. This novel capacitor composite materials would be a promising candidate for printed application in mobile telecommunication operations, especially in the frequency range of 0.5–3 GHz.

High-temperature reactions during the solid-state synthesis of samples from the (1-x)Na 0.5 Bi 0.5 TiO 3 –xSrTiO 3 system were investigated. Due to the number of chemically different elements, the processing of these ceramics is delicate and requires several firing steps under specific conditions to obtain phase-pure samples. Sintering in an air atmosphere resulted in a macroscopically inhomogeneous microstructure, which is a consequence of incomplete reaction between different secondary phases. However, prolongation of the sintering time aggregated the pores in the sample, while at a higher firing temperature the sample’s secondary phase melted. As a result, the nominal composition was altered, leading to the formation of the Na 2 Ti 6 O 13 secondary phase. Sintering under an increased oxygen pressure of 1 MPa limited the evaporation of the secondary phase. This allowed the completion of the reaction, forming a homogeneous and dense sample. The study provides a set of experimental conditions for the successful preparation of ceramics from the investigated system.

The conditions for the topochemical transformation of variously sized Bi4Ti3O12 template plates into BaTiO3 particles were studied in order to control their morphology, crystal structure, and preferential orientation. In the transformation from sub-200 nm- and μm-sized template plates in the presence of surplus BaCO3 (Bi4Ti3O12/BaCO3 = 1:10), the final BaTiO3 particles retained a memory of the precursor size when the conversion reaction in the molten salt (NaCl/KCl) occurred at 660 and 900 °C, respectively. In both cases the side length of the template was well preserved, while the thicknesses of the final BaTiO3 plates were larger compared to those of the templates. The morphology of the BaTiO3 particles formed from micrometer-sized Bi4Ti3O12 plates at 660 °C did not closely resemble the template shape because of the exfoliation and disintegration processes. Through the transformation of sub-200 nm Bi4Ti3O12 plates at 900 °C the formed BaTiO3 particles grew by Ostwald ripening, and thus also the shape of...

We developed a nanocomposite of Au nanoparticles, functionalized with arginine, and hydroxyapatite that contains Ga 3 + ions. This material possesses double antibacterial protection – a contact-based action by the functionalized gold nanoparticles and the antibacterial action of Ga 3 + ions. Here we show that the material is efficient against E. coli, S. epidermidis and P. aeruginosa and that the functionalized Au nanoparticles are mainly responsible for the antibacterial action against E. coli and S. epidermidis, while Ga 3 + ions are mainly responsible for the antibacterial action against P. aeruginosa. Such nanocomposites with combined antimicrobial effect present an innovative way for prevention and cure of bacterial infections and seem a promising human-friendly alternative for antibiotics and Ag-based antibacterial materials in treatments of infections by bacteria resistant to antibiotics.

Microwave properties of a novel and functional composite inorganic materials based on barium hexaferrite (BaFe 12 O 19 ) were measured and simulated. Three different inks with flake and sphere shape particles were developed and printed on the top of meander-shaped microwave inductor on alumina substrate. Several types of meandered inductors with a different number of turns were investigated for the verification of obtained results. The results show relative permeability values of 1.3, 2.2, and 1.5 for composite layers printed from the inks with flake shape at 41.5 wt.%, flake shape plus dodecyl benzene sulphonic acid (DBsa) at 44.4 wt.%, and sphere-like shape at 55.6 wt.% of BaFe 12 O 19 , respectively, at 3 GHz. Corresponding magnetic loss tangents were 0.015, 0.04, and 0.02. This novel inductor composite material can be applied for mobile telecommunication operations at 0.5 to 3 GHz frequency range.

The integration of epitaxial complex oxides with Si represents an invaluable opportunity for the creation of novel devices with logic and sensing capabilities, both implemented in the same chip. In this work, Pulsed Laser Deposition (PLD) is used to grow epitaxial ultra-thin (3–4 nm) SrTiO3 (STO) layers on Si(001), showcasing the possibilities of this technique for the growth of templates for the integration of complex oxides with Si. Our procedure involves the growth of a 1/2 monolayer (ML) of Sr buffer layer on the reconstructed Si(001) surface by PLD, the deposition of STO in inert Ar atmosphere, and latter oxidation and crystallization phases. The optimization of STO deposition, oxidation, and crystallization parameters proves to be essential for the improvement of the layer's quality. It has been found that the minimization of the thermal budget during the crystallization phase increases the interface sharpness, but a minimum temperature is needed for a proper densification of the STO layer. A coverage of 2 ML before every crystallization and oxidation phases was determined as the best balance between the critical thickness, minimization of the thermal budget, and a proper coverage of the buffer layer, which prevents its reactions with the Sr/Si surface. These results improve the general knowledge and understanding of metal oxide/silicon heterojunctions, and represent a solid stepping stone for the growth of high-quality thin STO templates on Si by PLD.

In this study we designed a multifunctional implant coating by exploiting the properties of vanadium pentoxide (V2O5), i.e., the antibacterial activity via myeloperoxidase-like catalytic activity and the bioactivity of low concentrations of vanadate ions (dissolved form of V2O5) via the insulin-mimicking effect. To achieve this, the dissolution control of the V2O5 and the sustained release of the vanadate ions had to be achieved by processing the appropriate carrier system for the V2O5. Thus, we evaluated the ability of different polymeric carriers and the V2O5 particle morphology to modulate in vitro the stability of the prepared V2O5/polymeric coatings. For the control of the V2O5 dissolution it was crucial to control the diffusion of the particles from the polymeric matrix to the surrounding medium and to prevent extensive swelling of the polymer matrix. We highlighted the correlation between the strength of the interactions at the V2O5/polymer interface and the composite's stability under simulated physiological conditions. The optimum outcome was obtained for a nanowires-V2O5/PLGA composite coating that delivered vanadates sustainably, while at the same time preventing the colonization of S. epidermidis (NCIMB 8853) on its surface and ensuring the absence of any harmful effects on the red blood cells.

Nearly stoichiometric Ti1.005S2 was prepared by a solid-state synthesis of the constituent elements and consolidated under a variety of processing conditions applied using pulsed-electric-current sintering. The non-stoichiometry in the Ti1 + xS2 induced during the sintering was quantitatively determined with a Rietveld structural refinement and a thermogravimetric analysis combined with inductively coupled plasma atomic emission spectroscopy. Significant cation off-stoichiometry and sulphur losses were already observed at a sintering temperature of 700 °C, resulting in heavily self-intercalated Ti1.076S2, which significantly altered the thermoelectric properties in comparison with the nearly stoichiometric compound. By applying a high sintering pressure of 500 MPa the Ti1.005S2 could be consolidated at 500 °C with no detectable sulphur loses and with a high bulk density of 97.6%. The sulphur volatilization in the TiS2 was also effectively suppressed up to 800 °C by using a gas-tight sintering mould, which resulted in the composition Ti1.017S2, prepared at 800 °C and 200 MPa, with an optimal thermoelectric figure of merit ZT equal to 0.32 at 375 °C. Keywords: Titanium disulphide, Thermoelectric materials, Pulsed electric current sintering, Structure-property relationship, Transport properties

Sustainable development focused on energy and material savings is driving attempts to decrease the thermal conductivity of heat insulation materials. Foamed glass is one of the most sustainable thermal insulation materials and has unique, load-bearing properties. In this study, contributions to the effective thermal conductivity were quantified for an open-porous-type foamed glass. Foamed samples were prepared by heating a mixture of waste flat glass, the foaming additives carbon and Mn 3O 4, and the nucleation agent TiO 2. The density of the foamed glass was 117 kg m −3 (total porosity 95.8 vol%) with a closed porosity of only 5.8 vol%. The latter was minimized by promoting partial crystallization. The thermal conductivity was 54.3 mW m −1 K −1 at atmospheric pressure. Fitting the pressure dependence of the thermal conductivity gave a base thermal conductivity of 26.7 ± 0.4 mW m −1 K −1, and a gaseous contribution of 27.7 ± 0.5 mW m −1 K −1 with a pore size of 0.77 ± 0.07 mm. Thus, the base thermal conductivity, which is attributed mainly to the thermal conduction in the solid phase, is much higher than in the case of fibrous glass insulation products.

Spherical (diameter 50–200 nm), flake- (diameter 40–200 nm), and disc-shaped (diameter 10–20 nm) BaFe12O19 nanoparticles were synthesized with a wet chemical method, and their permittivity, electric loss tangent, permeability, and magnetic loss tangent were measured in the 0.045–10 GHz range. The materials were prepared using a solution of 12% PMMA resin in a butyldiglycol solvent for 10–50 wt% filling content. Microstrip transmission-line perturbation was used to measure complex permeability and the split post dielectric resonator method was employed to measure dielectric properties. The frequency dependence of the permeability and permittivity spectra of the composites was affected by their shape and filling fraction. The composites made with spherical particles had higher permeability values (1.4–1.75) at 1 GHz than the composites made with flake (1.25–1.6) or disc particles (1.1–1.3), but the spherical particles caused more losses. The flake particle composite provided permeability and magnetic loss characteristics at both 1 GHz and 7 GHz superior to those of the sphere particle composite in low-loss RF applications. The magnetic loss tangent of PMMA/BaFe12O19 was 0.2–0.3 at 1 GHz, being lower than that of state-of-the-art PANI/BaFe12O19 composites. The sphere composite inks showed permeability values less than 1 at 1–4 GHz ferromagnetic resonance (FMR); they could be used as a tunable material in microwave applications. The sphere and flake composite inks also had sufficient printing quality for the screen-printing fabrication method.

The effect of BaTiO 3 particle shape on the properties of 0.98MgTiO 3 –0.02BaTiO 3 composite powders was characterized and analyzed using an indirectly coupled open-ended coaxial cavity resonator at gigahertz frequencies. Elongated micrometre sized BaTiO 3 particles were found to have a significantly stronger effect on permittivity when compared to composite powders having micro and nano sized spherical BaTiO 3 particles. Inclusion permittivities and dielectric loss tangents of composite powders increased from that of pure MgTiO 3 powder, 13.3 and 4.6 × 10 −3 , up to 15.7 and 1.7 × 10 −2 with needle shaped BaTiO 3 particles, respectively. The presented results give valuable information for tailoring the properties of dielectrics which can be utilized in the vast field of electronic component manufacturing.

MgO exhibits antibacterial activity via a contact-based mechanism, which makes the design of its surface crucial. For this reason we systematically studied the effect of the calcination temperature on the morphological and antibacterial characteristics of MgO microrods. We observed the nano-texturing of the microrod's surface at calcination temperatures higher than 700 °C. The prepared particles improved the antibacterial activity against Escherichia coli (E. coli, ATCC 47076), which was related to the enhanced contact with the bacteria. The optimal nano-texturing of the MgO microrods was achieved after calcination at 900 °C. These microrods eliminated the bacteria 75% faster than commercially available MgO nanoparticles, which we attributed to a reduced concentration of non-emissive defects at the MgO surface. In addition, the nano-textured microrods agglomerated far less than the commercial nanoparticles, which favours their further processing.

Modified hydroxyapatite with antibacterial properties and high biocompatibility with mammalian cells is very desirable in many biomedical applications. Here we study the incorporation of Ga3+ ions into hydroxyapatite to achieve such an effective biological response. Antibacterial action against P. aeruginosa and cytocompatibility with L929 mouse fibroblasts was examined in vitro for different hydroxyapatites with incorporated Ga3+ ions (HAp(Ga)). Different Ga(III) contents and HAp(Ga) morphologies were obtained by adding Ga3+ ions at different stages of the hydroxyapatite synthesis and varying the Ga3+ concentration. Ga3+ ions were incorporated into the hydroxyapatite precursor phases at the early stages of the hydroxyapatite synthesis and into the amorphous surface layer of the apatite crystals at the late stages or after the synthesis, which yielded a mixed Ca/Ga amorphous phosphate surface layer. Their incorporation into the precursor nuclei before crystal formation and growth reduced the size of the final HAp(Ga) to small apatite nanocrystals with a large fraction of the mixed Ca/Ga amorphous phosphate surface layer. The release of Ga3+ ions from the HAp(Ga) depended on the overall amount of Ga in the material, while the biological response was mediated by the composition of the amorphous surface layer. The mainly Ca-phosphate amorphous surface layer resulted in a low antibacterial efficiency, while the mainly Ga-phosphate amorphous surface layer resulted in a high antibacterial efficiency, but also cytotoxicity. Ga(III)-containing hydroxyapatite can be designed for an effective biological response by varying the HAp(Ga) size and the overall Ga content to achieve the desired composition of the amorphous surface layer. The optimum HAp(Ga) in this study contained 4 wt% of Ga(III) and was obtained by adding Ga3+ ions during transformation of the precursor octacalcium phosphate/hydroxyapatite crystals to the final hydroxyapatite crystals. It provides excellent control over the release of the Ga3+ ions, and joins together the high efficacy of the antimicrobial action and non-toxicity over a wide concentration range (from 0.3 g L−1 to at least 1 g L−1).

The formation of tetragonal BaTiO3 from K2Ti6O13 (K2T6) nanowires was examined under hydrothermal conditions at 100–240 °C. The morphology and the crystal structure of the BaTiO3 particles that grew via a dissolution–precipitation mechanism were controlled by the temperature and the concentrations of the NaOH and the K2T6. The degree of tetragonality of the formed BaTiO3 powders was quantitatively evaluated on the basis of a Rietveld crystal-structure refinement and compared with the results of Raman and DSC analyses. The powders consisted mainly of star-like BaTiO3 particles that formed at 100 °C and contained cubic (22%) and tetragonal (78%) phases with a low c/a value of 1.0042. The BaTiO3 particles changed their shape to dendritic and seaweed-like with an increase of temperature to 150 °C and 200–240 °C, respectively. According to the Rietveld analysis this increase of the temperature led to the formation of a tetragonal phase with a high c/a ratio (1.008–1.010), which dominated over the cubic and tetragonal phases with a low c/a (1.004–1.007). An increase in the K2Ti6O13 and NaOH concentrations was found to decrease the tetragonality of the formed BaTiO3 particles. The electron-diffraction patterns suggested a multidomain structure for the seaweed-like, mainly tetragonal, BaTiO3 particles.

Sub-solidus phase relations in the ternary CaO–La2O3–TiO2 system at 1400 °C in air were determined. The multi-phase samples were prepared by a solid-state reaction method, whereas the single-phase samples for the structure analysis of selected solid solutions were prepared by a wet-precipitation method in order to provide good homogeneity of the starting mixtures. The phases in the prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The oxides form seven ternary compounds in the equilibrium state, many solid solutions (which extend across a broad concentration region), and a large, single-phase area based on the CaTiO3 solid solution. The structures of several new phases – solid solutions on the tie lines CaTiO3–Ca3La4Ti3O15 and La2TiO5–Ca3La4Ti3O15 – were determined in detail.

Lead-free piezoelectrics are materials exhibiting great potential, particularly because of their extended strains under high fields. However, the reported electrical properties remain inconsistent due to difficulties related to sample preparation. Here, we describe peculiarities of the synthesis procedure and their influence on the electrical properties of K 0.5 Bi 0.5 TiO 3 ceramics. This synthesis is characterized by the formation of K- and Bi-rich secondary phases and a reaction with humidity, which has a strong impact on the dielectric, ferroelectric and piezoelectric properties. These are very much improved after prolonged sintering, ascribed to the elimination of the hygroscopic K 2 O-rich phase. This is reflected in a higher resistivity, density and grain size. The electrical properties are improved in terms of a decrease in the dielectric losses, a two-fold increase in the permittivity value at the maximum, an increase in the remanent polarization to 29 μC/cm 2 , and an increase in the small signal d 33 value from 40 to 120 pC/N.

New, commensurate members of the fluorite-related Bi3Nb1−xTaxO7 family were synthesized and their crystal structures, microstructures, and microwave (MW) dielectric properties were characterized. The incorporation of Ta into the tetragonal Bi3Nb1−xTaxO7 solid solution was found to gradually affect the density and the MW dielectric properties. The materials sintered at 870°C exhibited relative permittivities in the range k′ = 86–72, Q × f values from 793 to 1189 GHz and a positive temperature coefficient of resonant frequency from 88 to 12 ppm/K. The formation of the members of the fluorite-related solid solution along the Bi3Nb1−xTaxO7 composition depends on a phase transition, and thus their properties are compared within the compositional range. The correlations between their MW dielectric properties, compositions, crystal structures, and processing parameters were discussed in detail. Optimization of MW properties can be achieved by utilizing the ability of the Bi3Nb1−xTaxO7 solid solution that it undergoes a phase transformation from cubic to tetragonal structure which are both characterized by unique properties, under certain synthesis conditions.

Micrometer-sized structures consisting of TiO2 nanoparticles were prepared using the sol–gel technique in combination with the structure-directing agent triethanolamine (TEA). The interaction of the TEA with the hydrolyzed sol–gel products led to the formation of TEA titanate complexes, which then enabled the assembly of sol–gel-precipitated nanosized powders. A subsequent thermal treatment of these powders resulted in the formation of micrometer-sized structures consisting of TiO2 anatase and rutile nanoparticles. To characterize the prepared powders, FTIR spectroscopy, XRD analysis, the Brunauer-Emmett-Teller method (sBET), UV–Vis spectrometry and electron microscopy (FE-SEM, and TEM) were employed. The photocatalytic degradation of the azo dye known as methylene blue was monitored under UV and Vis irradiation and showed that the micrometer-sized structures consisting of TiO2 nanoparticles exhibited a similar photocatalytic activity to submicrometer-sized structures consisting of TiO2 nanoparticles prepared without TEA.

As an alternative to mechanical alloying, high temperature synthesis (HTS) of ultra-hard, super-abrasive AlMgB14 was performed under normal pressure. The reaction mixture consisted of elemental Al and B, whereas Mg was added in the form of a Mgprecursor which liberates elemental magnesium approximately 400 ºC above the melting point of Mg, in this way reducing its evaporation during heating-up. 95 wt % conversion to AlMgB14 and 5 wt % to MgAl2O4 was achieved. The synthesized AlMgB14 baseline powder, as well as mixtures of AlMgB14 consisting of 30, 50 and 70 wt% of TiB2, were hot pressed to near theoretical density. The various samples produced were characterized for microstructure and hardness. A microhardness of 29.4GPa in hot pressed AlMgB14 and a maximum Vickers hardness of 30.2 GPa in hot pressed samples of AlMgB14 reinforced with 70 wt% of TiB2 particles (d50=4,1µm) was achieved. Future project milestones necessary for achieving a higher AlMgB14 reaction yield, reducing the MgAl2O4 content and producing sinter-active AlMgB14 powder, as well as hot pressed composites processing improvement for gaining maximum hardness are also presented.

In order to avoid the potential health problems associated with nanosized particles, solvothermal synthesis was employed for the preparation of doped and undoped, hierarchically structured, spherical anatase, ranging in size from 2 to 6.4 μm. The resulting particles showed a mesoporous microstructure and, consequently, a high specific surface area of up to 208 m2 g−1. A detailed SEM analysis confirmed the hierarchical structure of the spheres, consisting of subunits with a size from 10 to 21 nm, depending on the starting composition. For the thermal stabilization of the anatase phase and to slow down the growth of the nanosize particles during heating, various dopants were added to the anatase. As a result, anatase codoped with Ce, Si and Zr exhibited a high thermal stability up to 1000 °C, compared to 700 °C for the undoped anatase. The photocatalytic activities of the synthesized solids were quantitatively evaluated by monitoring the rate of degradation for isopropanol in a gas phase reactor system. Among the samples that were heat treated at 500 °C, the highest photocatalytic activity was exhibited by the Ce-doped sample. In the case of the samples which were heat treated at 1050 °C, the undoped and Ce-doped samples were inactive under UV light, while the samples doped with Ce, Zr and Si exhibited considerable photocatalytic activity.

Lantibiotics, bacteria-sourced antimicrobial peptides, are very good candidates for effective and safe food additives. Among them, nisin is already approved by the EU and FDA, and has been used in food preservation for the past 40 years. Now, there is a possibility and strong interest to extend its applicability to biomedicine for designing innovative alternatives to antibiotics. The main obstacle is, however, its naturally narrow spectrum of antimicrobial activity, focused on Gram positive bacteria. Here we demonstrate broadening nisin’s spectrum to Gram negative bacteria using a nano-engineering approach. After binding nisin molecules to the surface of gold nano-features, uniformly deposited on spherical carbon templates, we created a nanocomposite with a high density of positively charged groups. Before assembly, none of the components of the nanocomposite showed any activity against bacterial growth, which was changed after assembly in the form of the nanocomposite. For the first time we showed that this type of structure enables interactions capable of disintegrating the wall of Gram negative bacteria. As confirmed by the nisin model, the developed approach opens up new horizons for the use of lantibiotics in designing post-antibiotic drugs.

The gas-releasing reaction is the most important process in the preparation of foam glass. In this paper we investigated the gas-releasing reactions by means of thermogravimetry coupled with mass spectrometry. We used carbon (activated charcoal and carbon black) and/or manganese oxides (MnO2, Mn2O3, and Mn3O4) as the foaming additives. We show that manganese oxides have different functions in the foaming process. The thermal decomposition of MnO2 below the sintering temperature has a negative impact on the foaming process as it shifts the foaming to higher temperatures, increases the mass-loss rate, leading to open pores, and burns out the carbon. When foaming in an oxidizing atmosphere, the carbon is burnt out by the oxygen from the atmosphere. Instead, Mn2O3 can be used as the foaming agent in an oxidizing atmosphere. In the oxygen-free atmosphere, Mn3O4 can be used as the oxidizing agent, supporting the oxidation of carbon and the foaming process. The redox equilibrium of manganese (Mn2+/Mn3+), influenced by the oxygen partial pressure in the pores and physically dissolved oxygen in the glass, shows the strongest influence on the foaming process. The CO/CO2 ratio in the evolved gases depends on the carbon source and the temperature.

Made available in DSpace on 2018-12-11T17:06:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Phase stability and microstructure evolution of polycrystalline CaCu3Ti4O12 (CCTO) ceramics were studied by controlling the partial pressure of oxygen (from a poor to an oxygen rich atmosphere) during the sintering process at high temperatures. The samples were analyzed by X-ray powder diffraction, scanning electron microscopy and X-ray energy dispersive spectroscopy. Our results show that the oxygen partial pressure during the sintering process is an important parameter that controls the phase stability, non-stoichiometry, and decomposition process of the CCTO phase as well as the densification and grain growth mechanisms on these polycrystalline ceramics. These results provided us further insight into the important role of copper reduction and copper/oxygen diffusion on the crystalline structure and morphological characteristics of polycrystalline CCTO ceramics. Physical Chemistry Department Chemistry Institute São Paulo State University (UNESP) Advanced Materials Department Jožef Stefan Institute Physical Chemistry Department Chemistry Institute São Paulo State University (UNESP) FAPESP: 09/00367-6 FAPESP: 13/07296-2 FAPESP: 13/14647-6

The epitaxial growth of functional oxides on silicon substrates requires atomically defined surfaces, which are most effectively prepared using Sr-induced deoxidation. The manipulation of metallic Sr is nevertheless very delicate and requires alternative buffer materials. In the present study the applicability of the chemically much more stable SrO in the process of native-oxide removal and silicon-surface stabilization was investigated using the pulsed-laser deposition technique (PLD), while the as-derived surfaces were analyzed in situ using reflection high-energy electron diffraction and ex situ using X-ray photoelectron spectroscopy, X-ray reflectivity, and atomic force microscopy. After the deposition of the SrO over Si/SiO2, in a vacuum, different annealing conditions, with the temperature ranging up to 850 degrees C, were applied. Because the deposition took place in a vacuum, a multilayer composed of SrO, Sr-silicate, modified Si, and Si as a substrate was initially formed. During the subsequent annealing the topmost layer epitaxially orders in the form of islands, while a further increase in the annealing temperature induced rapid desorption and surface deoxidation, leading to a 2 x 1 Sr-reconstructed silicon surface. However, the process is accompanied by distinctive surface roughening, and therefore the experimental conditions must be carefully optimized to minimize the effect. The results of the study revealed, for the first time, an effective pathway for the preparation of a SrO-induced buffer layer on a silicon substrate using PLD, which can be subsequently utilized for the epitaxial growth of functional oxides.

The dependence of the permittivity on the uniaxial compressive stress was investigated for the case of Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 ceramics. For the morphotropic sample the results showed a strong increase in the stress dependence compared to pure Na0.5Bi0.5TiO3. Nevertheless, a threshold stress was observed, below which the domain switching was hindered. The threshold stress value and, thus, the “hardness” of the materials increased with increasing K0.5Bi0.5TiO3 content. In the “hard” tetragonal samples the permittivity increased with the stress loading; however, if the mechanical load exceeded a threshold level, the “hardening” effect vanished. The results are discussed in terms of the defect dipole model for the stabilization of the domain configuration. The stabilization was the highest in pure K0.5Bi0.5TiO3, for which a poled remanent state was preserved at stresses higher than 200 MPa.

We have investigated the effect of oleic acid concentration on the physicochemical properties of solvothermally derived cobalt ferrite nanoparticles (CFO NPs). Without the oleic acid, agglomerated nanoplatelets with a crystallite size of about 19 nm were obtained, according to X-ray diffraction (XRD) and transmission electron microscopy (TEM). However, the addition of oleic acid decreases the size of the CFO NPs and at critical concentration, which was determined to be 0.25 M, well-dispersed, nonagglomerated spherical particles of about 6 nm were obtained. A further increase in the oleic acid concentration affected the particle size only slightly, with a relatively constant surface coverage of the oleic acid ligand. The results of our study indicate that particle-size control was achieved by bridging bidentate interactions between the oleic acid molecules and the metal atoms on the surface of the NPs, as determined by Fourier transform infrared spectra. These interactions affected the surface strain of NP...

AgNb 0.5 Ta 0.5 O 3 ceramics were synthesized and analyzed, with respect to their dielectric properties, in the radio- and microwave-frequency ranges. The influences of different synthesis conditions were investigated and correlated with the difficulties in preparing single-phase ceramics, as a consequence of the inhomogeneous distribution of Nb and Ta ions and the decomposition of the matrix phase. The results revealed that with the simple mixing of all three oxides and subsequent firing in air, it is possible to prepare composite material that is attractive for microwave applications due to inhomogeneity of the B-site cation distribution – a well-known issue that was in our case shown to be an advantage for decreasing the temperature dependence of the resonant frequency over a broad temperature range. On the other hand, we also succeeded in fabricating single-phase ceramics with a very high density through the initial formation of a precursor and sintering in an overpressure of oxygen.

Cobalt ferrite nanoparticles (CFO NPs) were synthesized using precipitation followed by a hydrothermal treatment. The conditions for precipitation were kept constant, while the pH, the temperature and the synthesis time for the hydrothermal treatment were systematically varied. The results show that the pH plays the dominant role in the formation, growth and crystallization of the desired phase. Furthermore, by controlling the pH the magnetic properties, such as the magnetization and the coercivity of the CFO NPs, can be tuned. An increase in the temperature induced both particle growth and a change of the morphology. The variation of the synthesis time indicated that the hydrothermal reaction proceeds for up to 8 h; however, a further prolongation of the synthesis time does not affect the structural and magnetic properties to any significant extent.

With the application of an oxygen atmosphere, we synthesized a highly textured sodium cobaltate, Na0.75CoO2. At the same time, we identified its peculiarities that influence the measured parameters to a degree that poses serious questions about this material’s potential for use. We have systematically studied the influence of humidity on the ceramic pellets and identified the conditions under which the material completely deteriorates. By performing microstructural and thermal analyses, coupled with a determination of the evolved gases, we identified the chemical reactions that are involved in this process. In addition, we re-examined the performance of sodium cobaltate under the working conditions and found that the material behaves in a manner different from the expected manner. We have shown, in contrast to many other reports, that the oxygen vacancies do not play a very important role because the changes in the physical parameters can be attributed to the reduction of cobalt and consequently to the fo...

The experimental conditions for the growth of shape-controlled BaTiO3 particles in NaOH and Ba(NO3)2 aqueous and water/ethanol solutions using various TiO2-containing precursors were studied at 80°C–100°C. The different chemistries and physical characteristics of the precursors resulted in different BaTiO3 formation rates and morphologies. Nanocrystalline anatase led to irregularly shaped BaTiO3 particles, whereas star-like, single-crystalline BaTiO3 particles grew from aerogel TiO2 and sodium titanate (NT) belts in alkaline aqueous solutions. With the addition of ethanol, the star-like BaTiO3 particles changed to square-like, the size of which decreased with an increase in the ethanol content. The electron microscopy observations supported a dissolution–precipitation mechanism as the primary reaction mechanism for the formation of BaTiO3 nanocrystals, which further aggregated into single-crystalline star- or square-like particles by oriented attachment. The modification in the water solution with ethanol is believed to influence both the nucleation and aggregation process and consequently influence the particle shape and size.

The microstructural evolution and its influence on magnetic properties in cobalt ferrite were investigated. The cobalt ferrite powders were prepared via a solid-state reaction route and then sintered at 1200 °C for 1, 2, and 16 h in air. The microstructures from sintered samples represented a bimodal distribution of grain size, which is associated with abnormal grain growth behavior. And thus, with increasing sintering time, the number and size of abnormal grains accordingly increased but the matrix grains were frozen with stagnant grain growth. In the sample sintered for 16 h, all of the matrix grains were consumed and the abnormal grains consequently impinged on each other. With the appearance of abnormal grains, the magnetic coercivity significantly decreased from 586.3 Oe (1 h sintered sample) to 168.3 Oe (16 h sintered sample). This is due to the magnetization in abnormal grains being easily flipped. In order to achieve high magnetic coercivity of cobalt ferrite, it is thus imperative to fabricate the fine and homogeneous microstructure.

Polycrystalline sol–gel-derived SrTiO3/Na0.5Bi0.5TiO3/SrTiO3 (ST/NBT/ST) thin films were designed to achieve the electrical isolation of the NBT, and to mediate the temperature dependency of the dielectric properties. Proper thermal annealing of particulate phase enabled us to achieve compositionally graded elemental profiles between individual ST and NBT layers. The dielectric and ferroelectric properties were investigated with respect to the electrical behavior of the monophasic ST and NBT thin films. The dielectric characteristics of the multilayer thin film were marked by a temperature stable behavior (temperature coefficient of dielectric constant of 780 ppm/°C) in the measured −50°C to 200°C range, frequency-independent response at room temperature and improved dielectric loss characteristics compared with the NBT; however, on the expense of decreased permittivity and a reduced ferroelectric stability. Nevertheless, stable dielectric properties were achieved and properties of multilayer may well be exploited in functional devices that demand insensitive operation over wide temperature and frequency ranges.

Two kinds of Sr2FeReO6 (SFRO) samples, pristine SFRO and Re-excess SFRO, were prepared and we visualized the local atomic structure in terms of cationic ordering in the prepared SFRO samples via high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM). HAADF-STEM results demonstrated the high degree of cationic ordering maintains in both the pristine SFRO and Re-excess SFRO samples. On the other hand, defective structures such as antiphase boundary and Re-deficient phase were observed dominantly in the pristine SFRO, and thus the poor magnetic property in the pristine SFRO is attributed to those defective structures related with the frustrated Fe/Re ordering.

We have investigated sol-precipitation, coupled with a hydrothermal treatment, as a common solution-based method for the preparation of SrTiO 3 nanostructured powders. XRD, FTIR, TG/EGA, Raman and TEM were employed for a detailed structural characterization of the sol-precipitates in comparison with subsequently hydrothermally or thermally post-annealed samples. The sol-precipitates exhibited a pseudo-cubic symmetry and adopted the morphology of the hydrolyzed Ti-precursor. The structural distortions were attributed to un-removed OH − groups and A-site vacancies, arising in the crystal lattice, as a result of a low-temperature diffusion-controlled reaction. Furthermore, we demonstrated that the microstructural characteristics of sol-precipitates are directly responsible for the formation of extended defects, i.e., nanocavities, within the single-crystalline particles, appearing independently of the selected post-annealing treatment, i.e., hydrothermal or thermal. The study revealed that local distortions and peculiarities on the microscale, introduced by sol-precipitation, were not completely restored under vigorous hydrothermal conditions, but rather provoked the formation of new microstructural defects with an additional treatment.

Ferroelectric (1− x )Na 0.5 Bi 0.5 TiO 3 – x NaTaO 3 (NBT–NTa) thin films, with 0.05 x 2 /TiO 2 /Pt substrate using a modified sol–gel method. The dielectric permittivity, the dielectric losses, the voltage-tunability and the ferroelectric behavior of the NBT–NTa thin films were investigated. The thin films with 5 mol% and 10 mol% NaTaO 3 showed a similar dielectric permittivity ( e ≈441 at 1 MHz) and voltage-tunability ( n r ≈42% at 370 kV/cm, 1 MHz), whereas the thin films with 30 mol% of NaTaO 3 had a lower dielectric permittivity ( e ≈370) and voltage-tunability ( n r ≈23%). The relaxor-type ferroelectric response in the thin films with 5 mol% NaTaO 3 was due to a decrease in the average grain size to below 150 nm, resulting in the appearance of single-domain grains.

This work examines the synthesis and characterization of crack-free, β-Bi2O3 thin films prepared on Pt/TiO2/SiO2/Si or corundum substrates using the sol-gel method. We observed that the Bi-based precursor has a pronounced influence on the β-Bi2O3 phase formation. Well-crystallized, single β-Bi2O3 thin films were obtained from Bi-2ethylhexanoate at a temperature of 400°C. In contrast, thin films deposited from Bi-nitrate and Bi-acetate resulted in non-single Bi2O3 phase formation. TEOS was used for the stabilization of the β-Bi2O3 phase. The phase composition of the thin films was characterized by means of X-ray diffraction (XRD), whereas the morphology and thickness of the thin films were studied using scanning electron microscopy (SEM). The β-Bi2O3 films' dielectric properties were characterized utilizing microwave-frequency measurement techniques: (1) the split-post dielectric resonator method (15 GHz) and (2) the planar capacitor configuration (1–5 GHz). The dielectric constant and dielectric loss measured at 15 GHz were 257 and 7.5 × 10−3, respectively.

Thin films with the composition 70 mol% Na0.5Bi0.5TiO3 + 30 mol% NaTaO3 were prepared by sol–gel synthesis and spin coating. The influence of the annealing temperature on the microstructural development and its further influence on the dielectric properties in the low- (kHz–MHz) and microwave-frequency (15 GHz) ranges were investigated. In the low-frequency range we observed that with an increasing annealing temperature from 550°C to 650°C the average grain size increased from 90 to 170 nm, which led to an increase in the dielectric permittivity from 130 to 240. The temperature-stable dielectric properties were measured for thin films annealed at 650°C in the temperature range between −25°C and 150°C. The thin films deposited on corundum substrates had a lower average grain size than those on Si/SiO2/TiO2/Pt substrates. The highest average grain size of 130 nm was obtained for a thin film annealed at 600°C, which displayed a dielectric permittivity of 130, measured at 15 GHz.

Using a simple organic bifunctional bridging linker, titanium dioxide (TiO2) nanoparticles were coupled with the Au nanoparticles to form TiO2/Au nanocomposites with a variety of Au loadings. This organic bifunctional linker, meso-2,3-dimercaptosuccinic acid, contains two types of functional groups: (i) the carboxyl group, which enables binding to the TiO2, and (ii) the thiol group, which enables binding to the Au. In addition, the organic bifunctional linker acts as a stabilizing agent to prevent the agglomeration and growth of the Au particles, resulting in the formation of highly dispersed Au nanoparticles. To form the TiO2/Au nanocomposites in a simple way, we deliberately applied a synthetic method that simultaneously ensures: (i) the capping of the Au nanoparticles and (ii) the binding of different amounts of Au to the TiO2. The TiO2/Au nanocomposites formed with this method show enhanced UV and Vis photocatalytic activities when compared to the pure TiO2 nanopowders.