Origin of discrepancy between electrical and mechanical anomalies in lead-free (K,Na)NbO3 -based ceramics

[EN] Ferroelectric polymorphic phase coexistence, associated with either the presence of a morphotropic phase boundary or a temperature-driven polymorphic phase transition, is currently acknowledged as the key to high piezoelectric activity and is searched when new perovskite materials are developed, like lead-free alternatives to state-of-the-art Pb(Zr,Ti)O3. This requires characterization tools that allow phase coexistence and transitions to be readily identified, among which measurements of the temperature dependences of Young's modulus and mechanical losses by dynamical mechanical analysis stand out as a powerful technique to complement standard electrical characterizations. We report here the application of this technique to (K1-xNax)NbO3-based materials, which are under extensive investigation as environmentally friendly high sensitivity piezoelectrics. The elastic anomalies associated with the different phase transitions are identified and are shown to be distinctively shifted in relation to the dielectric ones. The origin of this discrepancy is discussed with the help of temperature-dependent Raman spectroscopy and is proposed to be a characteristic of diffuse phase transitions.The authors would like to thank CAPES and the Sâo Paulo Research Foundation (FAPESP), Grants No. 2012/08457-7 and No. 2013/00134-7, for the financial support. M.A. also acknowledges funding from MINECO through the MAT2014-58816-R Project.Peer Reviewe

Combining eutectic solvents and pressurized liquid extraction coupled in-line with solid-phase extraction to recover, purify and stabilize anthocyanins from Brazilian berry waste

Pressurized techniques are straightforward for high-scale applications and highly controllable, which seems an excellent strategy for recovering unstable natural compounds. In this work, the main advance was the development of a platform based on the pressurized liquid extraction coupled in-line with a solid-phase extraction step (PLE-SPE) combined with the use of eutectic mixtures as solvents to promote an efficient extraction and purification of natural pigments from food wastes. Eutectic mixtures, conventionally known as (deep) eutectic solvents – (D)ES, are combinations of two or more substances with a lower melting point than any of their components. (D)ES are often referred as “green solvents” because they can potentially be more environmentally friendly than other solvents, especially volatile organic solvents (VOSs). Overall, (D)ES have the potential to contribute to the achievement of several of the SDGs (especially 3, 13, and 14) through their positive impacts on health, environment, and sustainable production and consumption practices. Thus, in this work, (D)ES were used as solvents to valorize Brazilian berry waste (Plinia cauliflora). Anthocyanins are the biomass's main compounds of commercial interest, mainly for food and cosmetic applications. However, there are several technological issues regarding color control due to their high sensitivity to light, heat, oxygen, and pH variations. Thus, the data achieved in this work highlighted the high efficiency and low environmental footprint of the PLE-SPE-(D)ES platform developed. The success of the downstream process here developed was proved by the high extraction efficiency and the purity level of the anthocyanins obtained. Besides, thermal stability analysis was evaluated, demonstrating that (D)ES are not only solvents but also stabilizing agents, improving the shelf-life of the extracted colorants.publishe

Regulamento da Millenium - Journal of Education, Technologies, and Health

PbMoO(4) micro-octahedrons were prepared by the coprecipitation method at room temperature without the presence of surfactants and processed in a conventional hydrothermal at different temperatures (from 60 to 120 degrees C) for 10 min. These micro-octahedrons were structurally characterized by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy, and its morphology was investigated by field-emission gun scanning electron microscopy (FEG-SEM). The optical properties were analyzed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra confirmed that the PbMoO(4) micro-octahedrons are characterized by a scheelite-type tetragonal structure. FEG-SEM micrographs points, out that these structures present a polydisperse particle size distribution in consequence of a predominant growth mechanism via aggregation of particles. In addition, it was observed that the hydrothermal conditions favored a spontaneous formation of micro-octahedrons interconnected along a common crystallographic orientation (oriented-attachment), resulting in self-organized structures. An intense blue PL emission at room temperature was observed in these micro-octahedrons when they were excited with a 350 nm wavelength. The origin of the PL emissions as well as its intensity variations are explained by means of a model based on both distorted [MoO(4)] and [PbO(8)] clusters into the lattice.CAPESCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPqFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPES

Intense blue and green photoluminescence emissions at room temperature in barium zirconate powders

Intense blue and green photoluminescence (PL) emissions were observed at room temperature in barium zirconate (BaZrO3) powders prepared by chemical method. The powders were analyzed by X-ray diffraction (XRD), X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption spectroscopy (EXAFS) and ultraviolet–visible (UV–vis) absorption spectroscopy. The XRD patterns indicated the presence of a secondary phase of BaCO3 in BaZrO3 powders heat treated at 773 K. K-edge XANES data revealed that Zr atoms presents in at least two Zr environments. EXAFS investigations showed strong bond length dispersion in the first coordination shell around Zr atoms. EXAFS analysis indicated that Zr atoms are coordinated by 6 oxygen in BaZrO3 powders heat treated at 973 K. UV–vis measurements suggested the presence of intermediary energy levels into the band gap of BaZrO3 powders heat treated at 773 K. The intense PL emission in BaZrO3 powders can be attributed to the two Zr environments or ZrO5–ZrO6 clusters.CAPESFAPESPCNPQLaboratório Nacional de Luz Síncrotron (LNLS

Investigation in SrTi'O IND.3'-CaTi'O IND.3'-PbTi'O IND.3' ternary thin films by dielectric proprieties and Raman spectroscopy

Dielectric and Raman scattering experiments were performed on polycrystalline Pb1−x−yCaxSryTiO3 thin films as a function of temperature. Temperature-dependent dielectric measurements revealed a decreasing ferroelectric-to-paraelectric phase transition temperature and peak dielectric permittivity showed a broad phase transition near room temperature with increasing levels of CaO12 and SrO12 clusters. Therefore, for higher levels of substitution, the possible random position of the CaO12 and SrO12 clusters leads to a diffuse state. At 100 kHz, the ferroelectric-to-paraelectric phase transition temperatures were 633, 495 and 206 K for PCST90 (Pb0.90Ca0.05Sr0.05TiO3), PCST70 (Pb0.70Ca0.15Sr0.15TiO3) and PCST30 (Pb0.30Ca0.35Sr0.35TiO3) thin films, respectively. The evolution of the Raman spectra was also studied as a function of temperature. The temperature dependence of the E(1TO) soft mode frequencies was used to characterize the phase transition. Raman peaks were observed above the ferroelectric-to-paraelectric phase transition temperature, although all optical modes should be inactive in Raman scattering. The origin of these modes was interpreted as a breakdown of the local cubic symmetry by the random distribution of CaO12 and SrO12 clusters.CNPqCAPESFAPESP/CEPID (06/53926-4)FAPESP/CEPID (08/53515-7)FAPESP/CEPID (06/51640-6

Visible PL phenomenon at room temperature in disordered structure of SrWO 4 powder

Abstract. The SrWO 4 (SWO) powders were synthesized by the polymeric precursor method and annealed at different temperatures. The SWO structure was obtained by X-ray diffraction and the corresponding photoluminescence (PL) spectra was measured. The PL results reveal that the structural order-disorder degree in the SWO lattice influences in the PL emission intensity. Only the structurally order-disordered samples present broad and intense PL band in the visible range. To understand the origin of this phenomenon, we performed quantum-mechanical calculations with crystalline and order-disordered SWO periodic models. Their electronic structures were analyzed in terms of band structure. The appearance of localized levels in the band gap of the order-disordered structure was evidenced and is a favorable condition for the intense PL to occur

Hydrothermal microwave: a new route to obtain photoluminescent crystalline BaTi'O IND.3' nanoparticles

Hydrothermal microwave method was used as a new route to synthesize pure BaTiO3 (BT) nanoparticles at 140°C for 10 min under rapid reacting with stoichiometric Ba/Ti ratio. The crystalline products were characterized by X-ray powder diffraction (XRD) and the structure was refined by the Rietveld method from the tetragonal structure, which was supported by the Ti K-edge X-ray absorption near-edge structure (XANES). The pre-edge of Ti in the XANES spectra indicated that titanium ions are localized in a nonregular octahedron. Typical FT-Raman spectra for tetragonal BaTiO3 nanoparticles presented well-defined peaks, indicating a substantial short-range order in the system. However, a scattering peak at 810 cm-1 was attributed to the presence of lattice OH- groups, commonly found in materials obtained by hydrothermal process. Besides, the peak at 716 cm-1 can be related to eventual Ba2+ defects in the BaTiO3 lattice. BaTiO3 (BT) nanoparticles presented spherical morphology with a non-uniform distribution of particle sizes. An intense and broad photoluminescence band was observed around the green color emission at room temperature. By means of an excitation energy of 2.54 eV (488 nm), it was noted that the maximum profile emission (2.2 eV) is smaller than the forbidden band gap energy of BaTiO3, indicating that certain localized levels within the band gap must exist.CAPESCNPqFAPES

Caracterização molecular do Cão Barbado da Terceira

Dissertação de Mestrado em Engenharia Zootécnica.Neste trabalho analisaram-se 257 animais da raça Cão Barbado da Terceira sendo caracterizados geneticamente, por doze microssatélites identificando-se um total de 79 alelos. A variabilidade genética foi estimada através das frequências alélicas, diversidade genética, heterozigocidade esperada e observada, probabilidade de identidade e verificação do equilíbrio de Hardy-Weinberg. Analisou-se as distâncias genéticas entre grupos pré-definidos consoante o ano de nascimento. Realizaram-se testes de paternidade comparando com os dados cedidos pelos criadores dos animais em questão, com bons resultados confirmando-se a compatibilidade com os progenitores na maioria dos casos. A população continua a manter variabilidade genética suficiente para não sofrer um processo de inbreeding, contudo deve ser dada atenção aos reprodutores a serem utilizados no futuro de forma a se conseguir uma maior heterozigocidade na raça para que haja uma evolução positiva da mesma. Desta forma os objectivos deste trabalho foram conseguidos, sendo este tipo de marcadores moleculares suficientemente informativos para esta caracterização.ABSTRACT: In this study 257 animals from the Cão Barbado da Terceira breed were analyzed, which were genetically characterized with twelve microsatellites, with a total of 79 alleles identified. The genetic variability was estimated through the allelic frequencies, genetic diversity, expected and observed heterozygosity, identity probability and verification of the Hardy-Weinberg equilibrium. There was also the analysis of the genetic distances between groups predefined according to the year of birth, as well as paternity tests by the comparison with the data provided by the breeders. Good results were obtained and the compatibility with the parents was confirmed in most cases. The population still maintains enough genetic variability in order not to undergo inbreeding however one should pay attention to the breeders to be used in the future, in a way to obtain a higher heterozygosity so there is a positive evolution of the breed. Therefore the aims of this study were achieved, and this type of molecular markers was sufficiently informative for this characterization