Search results for: M.P.F. Graça

Items from 1 to 20 out of 90 results

article

Temperature dependent upconversion and spectroscopic properties of Nd3+ doped barium bismuth tellurite glasses

Suresh Kumar J., Pavani K., S.R. Gavinho, Seshadri M., more

Journal of Non-Crystalline Solids > 2018 > 498 > C > 89-94

This work reports on the spectroscopic properties and temperature dependent NIR to visible upconversion of Nd³⁺ doped barium bismuth tellurite glasses. Raman spectrum analysis was performed to predict the maximum phonon energy. Spectroscopic parameters (Ω₂, Ω₄, Ω₆ and χ) and radiative properties of certain transitions of Nd³⁺ ions were calculated by applying Judd–Ofelt (J–O) theory. The concentration...

article

Impedance spectroscopy study of polyester/carbon nanotube composites

Z. Samir, Y. El Merabet, M.P.F. Graça, S. Soreto Teixeira, more

Polymer Composites > 39 > 4 > 1297 - 1302

The electrical properties of carbon nanotubes loaded in polyester polymer matrix were studied by using the impedance spectroscopy technique. The study was carried out in the frequency range between 100 Hz and 1 MHz and temperature between 170 and 400 K. Cole–Cole representation was used to interpret the impedance spectra of all the samples. The variation of the electrical conductivity, as a function...

article

The effect of bismuth on the structure, magnetic and electric properties of Co2MnO4 spinel multiferroic

H. Chouaya, M. Smari, I. Walha, E. Dhahri, more

Journal of Magnetism and Magnetic Materials > 2018 > 451 > C > 344-350

Mixed Co₂Mn_1−xBi_xO₄ (x = 0, x = 0.05 and x = 0.1) samples were prepared by the sol–gel method using the citric acid route and characterized by various techniques. The X-ray diffraction (XRD) and Raman spectroscopic analyses confirmed the formation of inverse spinel cubic structure with Fd3‾m space group. The introduction of Bismuth (Bi) into Co₂MnO₄ did not modify the ferrimagnetic character of the...

article

Effect of laser processing on physical properties of (Ba0.85Ca0.15Ti0.9Zr0.1O3) lead-free thick films fabricated by the electrophoretic deposition

E. Venkata Ramana, N.M. Ferreira, A. Mahajan, Marta C. Ferro, more

Journal of Physics and Chemistry of Solids > 2018 > 113 > C > 94-101

In this work, we have fabricated lead-free piezoelectric Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ thick films by the electrophoretic deposition (EPD) followed by a continuous-wave CO₂ laser annealing and demonstrated the effect of laser energy on the quality of the final product. Thick films annealed under optimized conditions, 50 W/15 min, show a controlled microstructure/density compared to those derived from higher...

article

Raman, EPR and ethanol sensing properties of oxygen-Vacancies SrTiO3-δ compounds

H. Trabelsi, M. Bejar, E. Dhahri, M.P.F. Graça, more

Applied Surface Science > 2017 > 426 > C > 386-390

Polycrystalline SrTiO_3-_δ powders with cubic perovskite phase were prepared by solid-state reaction method followed by the creation of oxygen vacancies δ-thermal activated. The Raman spectroscopic investigation was carried out in a frequency range of 100–2000cm⁻¹, and the second-order Raman modes were observed at room temperature. The Electron Paramagnetic Resonance (EPR) results revealed that SrTiO...

article

Photoluminescence varied by selective excitation in BiGdWO6:Eu3+ phosphor

K. Pavani, M.P.F. Graça, J. Suresh Kumar, A.J. Neves

Optical Materials > 2017 > 74 > C > 120-127

Eu³⁺ doped bismuth gadolinium tungstate (BGW), a simplest member of Aurivillius family of layered perovskites, was synthesized by solid-state reaction method. Structural characterisation has been performed by X-Ray diffraction (XRD), Raman spectroscopy, Fourier Transform Infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Band gap of the host matrix has been calculated using reflectance...

article

TSDC and impedance spectroscopy measurements on hydroxyapatite, β-tricalcium phosphate and hydroxyapatite/β-tricalcium phosphate biphasic bioceramics

P.R. Prezas, B.M.G. Melo, L.C. Costa, M.A. Valente, more

Applied Surface Science > 2017 > 424 > P1 > 28-38

Bone grafting and surgical interventions related with orthopaedic disorders consist in a big business, generating large revenues worldwide every year. There is a need to replace the biomaterials that currently still dominate this market, i.e., autografts and allografts, due to their disadvantages, such as limited availability, need for additional surgeries and diseases transmission possibilities....

article

Effect of oxygen vacancies on SrTiO3 electrical properties

H. Trabelsi, M. Bejar, E. Dhahri, M. Sajieddine, more

Journal of Alloys and Compounds > 2017 > 723 > C > 894-903

SrTiO_3-δ (δ = 0.075, 0.125 and 0.25) were prepared in two steps: the preparation of the parent compound SrTiO₃ by the solid state reaction method followed by the creation of oxygen vacancies δ, through a thermally activated process. X-ray diffraction analysis shows that all samples crystallize in the cubic structure with Pm3m space group. The grain's size distribution and the samples' surface characteristics...

article

Studies on dielectric dispersion, relaxation kinetics and a.c. conductivity of Na2OCuOSiO2 glasses mixed with Bi2O3-Influence of redox behavior of copper ions

J. Ashok, N. Purnachand, J. Suresh Kumar, M. Srinivasa Reddy, more

Journal of Alloys and Compounds > 2017 > 696 > C > 1260-1268

Na₂OCuOSiO₂ glasses mixed with different concentrations Bi₂O₃ (ranging from 0 to 20.0 mol%) were prepared. Various dielectric parameters viz., dielectric constant, ε′, loss tan δ, electric moduli, M, electrical impedance, Z, and also a.c. conductivity, σ _ac(ω), in the frequency region 100 Hz to 1 MHz and in the temperature region 200 K‒400 K were measured as a function of Bi₂O₃ concentration. The...

article

Effect of laser irradiation on lithium niobate powders

N.M. Ferreira, M.C. Ferro, M.P.F. Graça, F.M. Costa

Ceramics International > 2017 > 43 > 2 > 2504-2510

LiNbO₃ is a well-known material with high potential for many technological applications. However, conventional preparation techniques require high processing times at high temperatures. In this work, a new and fast approach is proposed, based on laser technology, envisaging obtaining bulk materials of LiNbO₃. ´powders. The influence of the laser processing parameters, namely time and incident power...

article

Structural and electrical properties of zinc tantalum borate glass ceramic

A. Siva Sesha Reddy, M.G. Brik, J. Suresh Kumar, M.P.F. Graça, more

Ceramics International > 2016 > 42 > 15 > 17269- 17282

In this work we have synthesized ZnO–Ta₂O₅–B₂O₃ glass ceramics with different concentrations of Ta₂O₅. The prepared samples were characterized by XRD, SEM and DSC techniques. The results of these studies indicated that the samples are embedded with well defined randomly distributed crystalline phases with Zn₃Ta₂O₈ as the predominant one. The volume fraction of the crystallinity seemed to be increasing...

article

Corrigendum to ‘Ba-doped ZnO nanostructure: X-ray line analysis and optical properties in visible and low frequency infrared’ [Ceram. Int. (2016) 12860–12867]

Reza Zamiri, Hossein Mahmoudi Chenari, H.F. Moafi, Mehdi Shabani, more

Ceramics International > 2016 > 42 > 14 > 16436

article

Structural influence of Bi3+ ions on physical properties of Na2CuSiO4 glasses photoluminescence and thermoluminescence studies

J. Ashok, J. Suresh Kumar, M.P.F. Graça, M.J. Soares, more

Journal of Non-Crystalline Solids > 2016 > 449 > C > 50-54

CuO doped sodium silicate glasses mixed with different concentrations of Bi₂O₃ are synthesized. Photoluminescence, thermoluminescence characteristics have been investigated. Photoluminescence emission spectra exhibited a broad band in the bluish green region under excitation at 325nm. This band is attributed to ³D₁→¹S₀transition of (Cu⁺)₂ pairs. The intensity of this emission band is observed to increase...

article

Ba-doped ZnO nanostructure: X-ray line analysis and optical properties in visible and low frequency infrared

Reza Zamiri, Hossein Mahmoudi Chenari, H.F. Moafi, Mehdi Shabani, more

Ceramics International > 2016 > 42 > 11 > 12860- 12867

In this work, X-ray diffraction analysis and optical properties of pure and Ba-doped ZnO nanoparticles prepared by the precipitation method were investigated. X-ray analysis was employed to evaluate the micro structural parameters of ZnO nanoparticles in terms of crystallite sizes and lattice strain by the Williamson–Hall method. The average crystallite size of Ba-doped ZnO nanoparticles estimated...

article

Synthesis, crystal structure, thermal analysis and dielectric properties of (C8H12N)3SnCl6.Cl compound

H. Chouaib, N. Elfaleh, S. Karoui, S. Kamoun, more

Synthetic Metals > 2016 > 217 > C > 129-137

A new compound of formula (C₈H₁₂N)₃SnCl₆·Cl is obtained at room temperature by slow evaporation of aqueous solution. Structural analysis indicates that this compound crystallizes in the monoclinic system with P2₁/C space group. The N–ZH⋯Cl hydrogen bonds between (C₈H₁₂N)⁺ cations, Cl⁻ anions and [SnCl₆]²⁻ dianions contribute to the cohesion and the stability of the atomic arrangement. One phase transition...

article

Niobium oxides and niobates physical properties: Review and prospects

C. Nico, T. Monteiro, M.P.F. Graça

Progress in Materials Science > 2016 > 80 > C > 1-37

For the last 75 years several studies have been reporting on the physical properties of niobium oxides, but there is still many contradictory, inconsistent and insufficient information on these metal oxides. This review will begin by describing the niobium oxygen system and the different stoichiometric and non-stoichiometric phases, specifically Nb, NbO, NbO₂, Nb₂O₅ and Nb₂O_5−δ. The crystalline phases...

article

Structural and electrical properties of TeO2–V2O5–K2O glassy systems

S.A. Salehizadeh, B.M.G. Melo, F.N.A. Freire, M.A. Valente, more

Journal of Non-Crystalline Solids > 2016 > 443 > C > 65-74

Ternary glasses with molar composition 50TeO₂–(50–x)V₂O₅–xK₂O, where 0≤x≤15, were prepared by the press-melt quenching method. Since this type of glasses shows promising application in electrochemical and thermoelectric devices, the structural and electrical properties of the glassy system presented above were investigated in the present work.In order to evaluate the structure of the prepared glasses,...

article

Hybrid microwave processing of Ca3Co4O9 thermoelectrics

K. Miyazawa, F. Amaral, A.V. Kovalevsky, M.P.F. Graça

Ceramics International > 2016 > 42 > 8 > 9482-9487

In this study, hybrid microwave sintering of Ca₃Co₄O₉ thermoelectric materials was implemented for the first time. Thermoelectric properties of samples sintered in different conditions and in conventional electrical furnace, using the same temperatures and dwell times, were assessed and compared. Microwave processing was found to promote densification and grain texturing in Ca₃Co₄O₉ bulk ceramics,...

article

Power dependent upconversion in Er3+/Yb3+ co-doped BiNbO4 phosphors

A.J.M. Sales, D.G. Sousa, H.O. Rodrigues, M.M. Costa, more

Ceramics International > 2016 > 42 > 6 > 6899-6905

In the present article, optical properties and energy upconversion in Er³⁺/Yb³⁺ co-doped BiNbO₄ matrix were investigated. The BiNbO₄ 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 Er³⁺ and Yb³⁺ on the sample surface were obtained by...

article

Nanodiamond-Fe3O4 nanofluids: Preparation and measurement of viscosity, electrical and thermal conductivities

L. Syam Sundar, E. Venkata Ramana, M.P.F. Graça, Manoj K. Singh, more

International Communications in Heat and Mass Transfer > 2016 > 73 > C > 62-74

Nanodiamond (ND) attached with magnetite (Fe₃O₄) nanoparticles have been synthesized successfully by in-situ and chemical reduction of Fe³⁺ and Fe²⁺ cations on the acid treated-ND surface by using sodium hydroxide as a reducing agent. The synthesized magnetic ND-Fe₃O₄ nanocomposite was characterized by XRD and TEM. The results indicate that Fe₃O₄ nanoparticles were homogeneously dispersed on the outer...

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Search results for: M.P.F. Graça

Temperature dependent upconversion and spectroscopic properties of Nd3+ doped barium bismuth tellurite glasses

Impedance spectroscopy study of polyester/carbon nanotube composites

The effect of bismuth on the structure, magnetic and electric properties of Co2MnO4 spinel multiferroic

Effect of laser processing on physical properties of (Ba0.85Ca0.15Ti0.9Zr0.1O3) lead-free thick films fabricated by the electrophoretic deposition

Raman, EPR and ethanol sensing properties of oxygen-Vacancies SrTiO3-δ compounds

Photoluminescence varied by selective excitation in BiGdWO6:Eu3+ phosphor

TSDC and impedance spectroscopy measurements on hydroxyapatite, β-tricalcium phosphate and hydroxyapatite/β-tricalcium phosphate biphasic bioceramics

Effect of oxygen vacancies on SrTiO3 electrical properties

Studies on dielectric dispersion, relaxation kinetics and a.c. conductivity of Na2OCuOSiO2 glasses mixed with Bi2O3-Influence of redox behavior of copper ions

Effect of laser irradiation on lithium niobate powders

Structural and electrical properties of zinc tantalum borate glass ceramic

Corrigendum to ‘Ba-doped ZnO nanostructure: X-ray line analysis and optical properties in visible and low frequency infrared’ [Ceram. Int. (2016) 12860–12867]

Structural influence of Bi3+ ions on physical properties of Na2CuSiO4 glasses photoluminescence and thermoluminescence studies

Ba-doped ZnO nanostructure: X-ray line analysis and optical properties in visible and low frequency infrared

Synthesis, crystal structure, thermal analysis and dielectric properties of (C8H12N)3SnCl6.Cl compound

Niobium oxides and niobates physical properties: Review and prospects

Structural and electrical properties of TeO2–V2O5–K2O glassy systems

Hybrid microwave processing of Ca3Co4O9 thermoelectrics

Power dependent upconversion in Er3+/Yb3+ co-doped BiNbO4 phosphors

Nanodiamond-Fe3O4 nanofluids: Preparation and measurement of viscosity, electrical and thermal conductivities

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