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In this study, the Pb(Zr0.65Ti0.35)O3 (PZT) structure was produced by the solid state reaction method, and a new polarization geometry was used to obtain the radial and thickness modes in cylindrical samples with more efficiency. The... more
In this study, the Pb(Zr0.65Ti0.35)O3 (PZT) structure was produced by the solid state reaction method, and a new polarization geometry was used to obtain the radial and thickness modes in cylindrical samples with more efficiency. The polarization procedure was investigated by varying the temperature from 30°C to 80°C. The experimental excitation of radial and thickness modes was observed, and a comparative study was performed with numerical simulations. The comparative analysis of the acoustic response of the cylindrical PZT samples under theoretical and experimental conditions was validated by COMSOL Multiphysics® software. The new polarization geometry technique was used to generate radial thickness and acoustic mixed modes with more efficiency. The results show that the resonance frequency and antiresonance, as well as the impedance mode and phase angle are well adjusted, showing the validation of the technique presented between the theoretical and experimental measurements.
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O presente artigo e resultado de um projeto de pesquisa realizado com o objetivo de analisar os livros didaticos de Matematica do Ensino Fundamental utilizado em uma escola publica de Nova Andradina. Observar como a argumentacao esta... more
O presente artigo e resultado de um projeto de pesquisa realizado com o objetivo de analisar os livros didaticos de Matematica do Ensino Fundamental utilizado em uma escola publica de Nova Andradina. Observar como a argumentacao esta presente no ensino da matematica e na construcao dos raciocinios dedutivo, indutivo, abdutivo. Traz a analise do conteudo envolvendo a relacao dos ângulos formados por duas retas paralelas cortadas por uma reta transversal. Os resultados mostram que ha por parte da colecao uma preocupacao em fixar um topico de cada vez, fica ao aluno a tarefa de estabelecer relacoes, e deixam pouco espaco para que haja uma discussao de ideias e na construcao do raciocinio.
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The development of new materials with a high dielectric constant and low losses is one of the main targets in scientific research for applications. These properties permit to reduce the size and weight of electronic devices. A potential... more
The development of new materials with a high dielectric constant and low losses is one of the main targets in scientific research for applications. These properties permit to reduce the size and weight of electronic devices. A potential candidate for this goal is yttrium ferrite. Powder precursors of yttrium ferrites, Y3Fe5O12 (YIG) and YFeO3, were prepared by the sol-gel method through the Pechini route. The powders were heat-treated at 1000, 1300 and 1400 °C. The sample structure was characterized by X-ray diffraction (XRD), the morphology by scanning electron microscopy (SEM). For all temperatures of the heat-treatment, the YIG crystalline phase was the predominant and YFeO3 the secondary phase. The highest percentage of YIG (≈90%) was obtained in the samples heat-treated at 1400 °C. By means of impedance spectroscopy measurements, the dielectric properties were studied between 100 Hz and 1 MHz, and between 200 and 400 K. The dielectric constant improves with the growth of the YI...
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Lithium ferrite (LiFe5O8) in the cubic crystal system is a very important and versatile material for several technological applications as it possesses very attractive electric and magnetic behaviors. Herein, we report an ecofriendly... more
Lithium ferrite (LiFe5O8) in the cubic crystal system is a very important and versatile material for several technological applications as it possesses very attractive electric and magnetic behaviors. Herein, we report an ecofriendly first approach sol-gel route, mediated by pectin, for the preparation of LiFe5O8. Pectin, a natural polysaccharide, was explored because it is a very attractive gelling agent to produce ceramic materials by the sol-gel method. The influence of the sintering temperature (800–1200 °C) applied on the pressed pellets, was evaluated by correlating the electric and magnetic properties with its structural and morphological characteristics. LiFe5O8 pellets sintered at 1000 and 1100 °C had the lowest dielectric losses and the most interesting dielectric behaviors in this regard, due to quasi-independence of the loss tangent through the temperature and frequency range studied. The magnetization, at 300 K, of LiFe5O8 monophasic pellets, sintered at 1100 and 1200 °C, are among the best values reported in the literature, 65 and 71 emu/g, respectively. Thus, the LiFe5O8 prepared by this sol-gel route shows particularly notable magnetic properties that can be explored for several applications. Tuning the magnetic and electric behavior of lithium ferrite using an eco-friendly pectin sol-gel route Tuning the magnetic and electric behavior of lithium ferrite using an eco-friendly pectin sol-gel route LiFe5O8 particles were prepared by a Pectin mediated sol-gel route. LiFe5O8 sintered at 1000 and 1100 °C had low dielectric losses. The loss tangent is quasi-independence on the temperature and frequency. The magnetization of monophase LiFe5O8 achieved 71 emu/g, at 300 K. LiFe5O8 particles were prepared by a Pectin mediated sol-gel route. LiFe5O8 sintered at 1000 and 1100 °C had low dielectric losses. The loss tangent is quasi-independence on the temperature and frequency. The magnetization of monophase LiFe5O8 achieved 71 emu/g, at 300 K.
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Abstract Studies indicate that the degree of polymorphism of niobium pentoxide (Nb2O5) is related to the origin of its extraction and that adequate heat treatments can improve its quality concerning the number of structural phases. In... more
Abstract Studies indicate that the degree of polymorphism of niobium pentoxide (Nb2O5) is related to the origin of its extraction and that adequate heat treatments can improve its quality concerning the number of structural phases. In this study, the niobium pentoxide extracted from the region of the Triângulo Mineiro in the state of Minas Gerais in Brazil was heat treated and its structural characterization reveals to obtaining the single monoclinic phase (H-Nb2O5). The thermal treatments were carried out from 900 to 1150 °C and the desired single-crystal phase sample was obtained with the treatment at 1100 °C. The treated material was characterized by Dynamic Light Scattering (DLS), and its morphology by scanning electron microscopy (SEM). X-ray diffraction (XRD) and Rietveld refinement show the presence of the crystalline phase and a good agreement between the experimental and the calculated results were obtained. Functional groups, characteristic bands, and peaks were analyzed by infrared spectroscopy using Fourier Transform with Photoacoustic Detection (FTIR-PAS) and Raman spectroscopy. Thermal analysis was also made using thermogravimetric analysis (TGA), differential thermal analysis (DTA), and dilatometry techniques.
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Abstract Hench et al. developed in 1969 the 45S5 Bioglass® showing high biocompatibility and osteogenic ability, enabling its application in bone tissue engineering. However, the bioactivity level and other physical and chemical... more
Abstract Hench et al. developed in 1969 the 45S5 Bioglass® showing high biocompatibility and osteogenic ability, enabling its application in bone tissue engineering. However, the bioactivity level and other physical and chemical properties can be compromised by structural changes. It is also known that the bone growth kinetics is related to the electrical characteristics of the bioglass. This manuscript presents an extensive study on the structural characteristics of the 45S5 Bioglass® endorsing the electrical properties with the structural and morphologic changes established by controlled heat-treatments. The bioglass was synthesized by melt-quenching and the heat-treatments were made at several temperatures from 500 up to 1000 °C. XRD, Raman and FTIR spectra show the occurrence of glass crystallization for treatments above 600 °C, in agreement with the thermal analysis of the base glass. The main phase, in the glass-ceramic samples, is Na2Ca2Si3O9, presenting a secondary phase in the sample treated above 900 °C. SEM micrographs show nanosize particles in the glass-ceramics, except for the sample treated at 1000 °C, which presents submicron-size. The electrical measurements revealed that the crystal phase dominates the conduction process and the dipoles arising from the interfaces lead to relaxations phenomena.
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Nowadays, the development of sustainable high-performance functional nanomaterials is on the spotlight. In this work, we report the preparation of a new generation of flexible and high electro-conductive nanopapers based on... more
Nowadays, the development of sustainable high-performance functional nanomaterials is on the spotlight. In this work, we report the preparation of a new generation of flexible and high electro-conductive nanopapers based on nanofibrillated cellulose (NFC) and copper nanowires (CuNWs). Homogeneous red-brick nanopapers (thickness: 30.2-36.4 μm) were obtained by mixing different amounts of NFC aqueous suspensions and CuNWs (1, 5, 10, 20, and 50 wt.%), followed by vacuum filtration and drying. SEM and EDS analysis confirmed the incorporation of the different amounts of CuNWs, and their uniform and random distribution. All the nanomaterials displayed good mechanical properties, viz. Young's modulus = 2.62-4.72 GPa, tensile strength = 30.2-70.6 MPa, and elongation at break = 2.3-4.1% for the nanopapers with 50 and 1 wt.% of CuNWs mass fraction, respectively. The electrical conductivity of these materials strongly depends on the CuNWs content, attaining a value of 5.43 × 104 S·m-1 for the nanopaper with the higher mass fraction. This is one of the highest values reported so far for nanocellulose based conductive materials. Therefore, these nanopapers can be seen as an excellent inexpensive and green alternative to current electro-conductive materials for applications in electronic devices, energy storage or sensors.
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Abstract In the present article, optical properties and energy upconversion in Er 3+ /Yb 3+ co-doped BiNbO 4 matrix were investigated. The BiNbO 4 matrix was prepared using the solid-state reaction method. X-ray diffraction of the matrix... more
Abstract In the present article, optical properties and energy upconversion in Er 3+ /Yb 3+ co-doped BiNbO 4 matrix were investigated. The BiNbO 4 matrix was prepared using the solid-state reaction method. X-ray diffraction of the matrix shows that the crystal structure is consistent with ICSD code 74338. The grain distribution and the behavior of doping with Er 3+ and Yb 3+ on the sample surface were obtained by scanning electron microscope. Raman spectral characterization was carried out to examine the behavior of the vibrational modes of the samples. Upconversion emissions in the visible region at 484.5, 522, 541.5 and 670.5 nm in the matrices BiNbO 4 :Er,Yb and BiNbO 4 :Er were observed and analyzed as a function of 980 nm laser excitation power and rare-earth doping concentration. The results show that BiNbO 4 is a promising host material for efficient upconversion phosphors.
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Variation of two and three photon upconversion band intensities in LNO:Er1%–Yb7.5% phosphor with temperature.
Research Interests: Materials Science, Doping, Lanthanum, RSC, Photon, and 2 morePHOSPHOR and Photon Upconversion(PHOSPHOR and Photon Upconversion)
(PHOSPHOR and Photon Upconversion)
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In this paper is reported an experimental and numerical investigation of the microwave dielectric properties of Na2Nb4O11 (NN), ceramic matrix added with (0, 2, 5, and 10 wt%) of Bi2O3, obtained through a new procedure based on the... more
In this paper is reported an experimental and numerical investigation of the microwave dielectric properties of Na2Nb4O11 (NN), ceramic matrix added with (0, 2, 5, and 10 wt%) of Bi2O3, obtained through a new procedure based on the solid‐state method. The experimental and theoretical characteristics of the resonator like return loss, bandwidth, input impedance are in good agreement. The simulations of radiation patterns are presented. For NN reference sample, frequency response bandwidth is of 43MHz (simulated) and 35MHz (experimental) for frequency operation around 2.28 GHz. The NN reference sample showed a dielectric permittivity around 58.4, with loss around 7.3 × 10− 3. The adding of bismuth oxide (2 and 5 wt%) reduced the value of the dielectric permittivity, otherwise the adding of 10 wt% increases its value. The temperature coefficient of resonant frequency (τf) was also measured for all dielectric samples. The values obtained were in the range of −3378 to −250ppm/°C. The results obtained confirm the necessity of producing composites of this material with others positive τf materials for obtaining dielectric resonator antennas with τf = 0. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1211–1217, 2016
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In this paper, the structural and dielectric properties of BNO (BiNbO4) was investigated as a function of the external RF frequency and temperature. The BNO Ceramics, prepared by the conventional mixed oxide method and doped with 3, 5 and... more
In this paper, the structural and dielectric properties of BNO (BiNbO4) was investigated as a function of the external RF frequency and temperature. The BNO Ceramics, prepared by the conventional mixed oxide method and doped with 3, 5 and 10 wt. % Bi2O3–PbO were sintered at 1,025 °C for 3 h. The X-ray diffraction patterns of the samples sintered, shown the presence of the triclinic phase (β-BNO). In the measurements obtained at room temperature (25 °C) was observed that the largest values of dielectric permittivity (ε′r) at frequency 100 kHz, were for the samples: BNO5Bi (5 wt. % Bi2O3) and BNO5Pb (5 wt. % PbO) with values ε′r ~ 59.54 and ε′r ~ 78.44, respectively. The smaller values of loss tangent (tan δ) were for the samples: BNO5Bi and BNO3Pb (3 wt. % PbO) with values tan δ ~ 5.71 × 10−4 and tan δ ~ 2.19 × 10−4, respectively at frequency 33.69 MHz. The analysis as a function of temperature of the dielectric properties of the samples, obtained at frequency 100 kHz, showed that the larger value of the relative dielectric permittivity was about ε′r ~ 76.4 at temperature 200 °C for BNO5Pb sample, and the value smaller observed of dielectric loss was for BNO3Bi sample at temperature 80 °C, with about tan δ ~ 5.4 × 10−3. The Temperature Coefficient of Capacitance (TCC) values at 1 MHz frequency, present a change of the signal from BNO (−55.06 ppm/°C) to the sample doped of Bi: BNO3Bi (+86.74 ppm/°C) and to the sample doped of Pb: BNO3Pb (+208.87 ppm/°C). One can conclude that starting from the BNO one can increase the doping level of Bi or Pb and find a concentration where one have TCC = 0 ppm/°C, which is important for temperature stable materials applications like high frequency capacitors. The activation energy (H) obtained in the process is approximately 0.55 eV for BNO sample and increase with the doping level. These samples will be studied seeking the development ceramic capacitors for applications in radio frequency devices.
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This study reports the synthesis of polyurethane–lignin copolymer blended with carbon multilayer nanotubes to be used in all-solid-state potentiometric chemical sensors. Known applicability of lignin-based polyurethanes doped with carbon... more
This study reports the synthesis of polyurethane–lignin copolymer blended with carbon multilayer nanotubes to be used in all-solid-state potentiometric chemical sensors. Known applicability of lignin-based polyurethanes doped with carbon nanotubes for chemical sensing was extended to eucalyptus LignoBoost® kraft lignin containing increased amounts of polyphenolic groups from concomitant tannins that were expected to impart specificity and sensitivity to the sensing material. Synthesized polymers were characterized using FT-MIR spectroscopy, electrical impedance spectroscopy, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry and are used for manufacturing of all solid-state potentiometric sensors. Potentiometric sensor with LignoBoost® kraft lignin-based polyurethane membrane displayed theoretical response and high selectivity to Cu (II) ions, as well as long-term stability.
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ABSTRACT In this paper a study of TiO2 addition (0, 2, 5 and 10 wt%) and its effects in the impedance spectra of Na2Nb4O11 ceramic matrix was carried out. The structural, dielectric properties of the addition in the Na2Nb4O11 matrix were... more
ABSTRACT In this paper a study of TiO2 addition (0, 2, 5 and 10 wt%) and its effects in the impedance spectra of Na2Nb4O11 ceramic matrix was carried out. The structural, dielectric properties of the addition in the Na2Nb4O11 matrix were discussed. In the preliminary structural studies, X-ray diffractograms of the samples were recorded at room temperature with X-ray diffractometer with Cu-kα. The Rietveld refinement method was used and confirmed the monoclinic structure for pure sample. A study based on complex impedance spectroscopy was carried and the dielectric properties were obtained over a frequency range (100 Hz–1 MHz) in room temperature (300 K). In the dielectric analysis at 1 MHz was observed relative permittivity of 99.46 for pure sample and 84.37 to sample added with 5 wt% of TiO2, those samples showed losses 3.55 × 10−2 and 9.22 × 10−2, respectively. In relation to relaxation phenomenon, Cole–Cole function was used for fitting pure and added samples data.
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In this paper a study of TiO2 addition (0, 2, 5 and 10 wt%) and its effects in the impedance spectra of Na2Nb4O11 ceramic matrix was carried out. The structural, dielectric properties of the addition in the Na2Nb4O11 matrix were... more
In this paper a study of TiO2 addition (0, 2, 5
and 10 wt%) and its effects in the impedance spectra of
Na2Nb4O11 ceramic matrix was carried out. The structural,
dielectric properties of the addition in the Na2Nb4O11
matrix were discussed. In the preliminary structural studies,
X-ray diffractograms of the samples were recorded at
room temperature with X-ray diffractometer with Cu-ka.
The Rietveld refinement method was used and confirmed
the monoclinic structure for pure sample. A study based on
complex impedance spectroscopy was carried and the
dielectric properties were obtained over a frequency range
(100 Hz–1 MHz) in room temperature (300 K). In the
dielectric analysis at 1 MHz was observed relative permittivity
of 99.46 for pure sample and 84.37 to sample
added with 5 wt% of TiO2, those samples showed losses
3.55 9 10-2 and 9.22 9 10-2, respectively. In relation to relaxation phenomenon, Cole–Cole function was used for
fitting pure and added samples data.
and 10 wt%) and its effects in the impedance spectra of
Na2Nb4O11 ceramic matrix was carried out. The structural,
dielectric properties of the addition in the Na2Nb4O11
matrix were discussed. In the preliminary structural studies,
X-ray diffractograms of the samples were recorded at
room temperature with X-ray diffractometer with Cu-ka.
The Rietveld refinement method was used and confirmed
the monoclinic structure for pure sample. A study based on
complex impedance spectroscopy was carried and the
dielectric properties were obtained over a frequency range
(100 Hz–1 MHz) in room temperature (300 K). In the
dielectric analysis at 1 MHz was observed relative permittivity
of 99.46 for pure sample and 84.37 to sample
added with 5 wt% of TiO2, those samples showed losses
3.55 9 10-2 and 9.22 9 10-2, respectively. In relation to relaxation phenomenon, Cole–Cole function was used for
fitting pure and added samples data.