Theoretical investigation of electronic and optical properties of andalusite within density functional theory

The electronic and optical properties of andalusite were studied by using quantum-mechanical calculations based on the density functional theory (DFT). The electronic structure shows that andalusite has a direct band gap of 5.01 eV. The complex dielectric function and optical constants, such as extinction coefficient, refractive index, reflectivity and energy-loss spectrum, are calculated. The optical properties of andalusite are discussed based on the band structure calculations. It is shown that the O-2p states and Al-3s states play a major role in optical transitions as initial and final states, respectively. (C) 2010 Elsevier Ltd. All rights reserved.

The electronic and optical properties of sodalite (Na(8)Al(6)Si(6)O(24)Cl(2)) from first principles

This study reports the results of ab initio electronic and optical calculations for pure socialite crystal using the linear augmented plane wave (LAPW) method within density functional theory (DFT). The calculated electronic structure revealed predominantly orbital characters of the valence band and the conduction band, and enabled us to determine the type and the value of the fundamental gap of the compound. The imaginary part of the dielectric tensor, extinction coefficient and refraction index were calculated as functions of the incident radiation wavelength. It is shown that the O 2p states and Na 3s states play the major role in optical transitions as initial and final states, respectively. The absorption spectrum is localized in the ultraviolet range between 40 and 250 nm. Furthermore, we concluded that the material does not absorb radiation in the visible range. (C) 2009 Elsevier Ltd. All rights reserved.

Influence of different solvents on the structural, optical and morphological properties of CdS nanoparticles

CdS is one of the most important II-VI semiconductors, with applications in solar cells, optoelectronics and electronic devices. CdS nanoparticles were synthesized via microwave-assisted solvothermal technique. Structural and morphological characterization revealed the presence of crystalline structures presenting single phase with different morphologies such as ""nanoflowers"" and nanoplates depending on the solvent used. Optical characterization was made by diffuse reflectance and photoluminescence spectroscopy, revealing the influence of the different solvents on the optical properties due to structural defects generated during synthesis. It is proposed that these defects are related to sulfur vacancies, with higher concentration of defects for the sample synthesized in ethylene glycol in comparison with the one synthesized in ethylene diamine. (C) 2011 Elsevier B.V. All rights reserved.

Microstructural, structural and dielectric properties of Er(3+)-modified BaTi(0.85)Zr(0.15)O(3) ceramics

The (micro)structural and electrical properties of undoped and Er(3+)-doped BaTi(0.85)Zr(0.15)O(3) ceramics were studied in this work for both nominal Ba(2+) and Ti(4+) substitution formulations. The ceramics were produced from solid-state reaction and sintered at 1400 degrees C for 3 h. For those materials prepared following the donor-type nominal Ba(1-x)Er(x)(Ti(0.85)Zr(0.15))O(3) composition, especially, Er(3+) however showed a preferential substitution for the (Ti,Zr)(4+) lattice sites. This allowed synthesis of a finally acceptor-like, highly resistive Ba(Ti,Zr,Er)O(3-delta)-like system, with a solubility limit below but close to 3 cat.% Er(3+). The overall phase development is discussed in terms of the amphoteric nature of Er(3+), and appears to mainly or, at least, partially also involve a minimization of stress effects from the ion size mismatch between the dopant and host cations. Further results presented here include a comparative analysis of the behavior of the materials` grain size, electrical properties and nature of the ferroelectric-to-paraelectric phase transition upon variation of the formulation and Er(3+) content. (C) 2008 Elsevier Ltd. All rights reserved.

Microstructural, structural and electrical properties of La(3+)-modified Bi(4)Ti(3)O(12) ferroelectric ceramics

Bi(4-x)La(x)Ti(3)O(12) (BLT) ceramics were prepared and studied in this work in terms of La(3+)-modified microstructure and phase development as well as electrical response. According to the results processed from X-ray diffraction and electrical measurements, the solubility limit (XL) of La(3+) into the Bi(4)Ti(3)O(12) (BIT) matrix was here found to locate slightly above x = 1.5. Further, La(3+) had the effect of reducing the material grain size, while changing its morphology from the plate-like form, typical of BIT ceramics, to a spherical-like one. The electrical results presented and discussed here also include the behavior of the temperature of the ferroelectric-paraelectric phase transition as well as the normal or diffuse and/or relaxor nature of this transition depending on the La(3+) content. (c) 2008 Elsevier Ltd. All fights reserved.

Thermoluminescence, structural and magnetic properties of a Li(2)O-B(2)O(3)-Al(2)O(3) glass system doped with LiF and TiO(2)

A Li(2)O-B(2)O(3)-Al(2)O(3) glass system, un-doped and doped with LiF, and/or TiO(2) was synthesized by the fusion method and its physical properties were investigated by thermoluminescence (TL), X-ray diffraction (XRD), electron paramagnetic resonance (EPR), atomic force microscopy (AFM) and differential thermal analysis (DTA). The samples were subjected to gamma-rays from a colbalt-60 ((60)Co) source. These techniques provided evidence of LiF and LiF doped with Ti crystal formation in the glass system. A TL glow peak at about 433 K was sensitive to (60)Co gamma-rays and showed good linearity with doses and consequently could be used to quantify radiation doses. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Structure and optical properties of [Ba(1-x)Y(2x/3)](Zr(0.25)Ti(0.75))O(3) powders

[Ba(1-x)Y(2x/3)](Zr(0.25)Ti(0.75))O(3) powders with different yttrium concentrations (x = 0, 0.025 and 0.05) were prepared by solid state reaction. These powders were analyzed by X-ray diffraction (XRD). Fourier transform Raman scattering (FT-RS), Fourier transform infrared (FT-IR) and X-ray absorption near-edge (XANES) spectroscopies. The optical properties were investigated by means of ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. Even with the addition of yttrium, the XRD patterns revealed that all powders crystallize in a perovskite-type cubic structure. FT-RS and FT-IR spectra indicated that the presence of [YO(6)] clusters is able to change the interaction forces between the O-Ti-O and O-Zr-O bonds. XANES spectra were used to obtain information on the off-center Ti displacements or distortion effects on the [TiO(6)] clusters. The different optical band gap values estimated from UV-vis spectra suggested the existence of intermediary energy levels (shallow or deep holes) within the band gap. The PL measurements carried out with a 350 nm wavelength at room temperature showed that all powders present typical broad band emissions in the blue region. (C) 2010 Elsevier Masson SAS. All rights reserved.

Preparation and structural characterization of rare-earth doped lead lanthanum zirconate titanate ceramics

A new preparation route towards rare-earth (RE) doped polycrystalline lead lanthanum zirconate titanate (PLZT) ceramics (RE = Y(3+), Nd(3+), Yb(3+)), based on the use of doped lanthanum oxide or zirconia, is reported. Structural characterization by X-ray powder diffraction reveals that secondary phase formation can be substantially diminished in comparison to conventional preparation methods. The distribution of the rare-earth dopants was investigated as a function of concentration by static (207)Pb spin echo NMR spectra, using Fourier Transformation of Carr-Purcell-Meiboom-Gill spin echo trains. For the Nd- and Yb-doped materials, the interaction of the (207)Pb nuclei with the unpaired electron spin density results in significant broadening and shifting of the NMR signal, whereas these effects are absent in the diamagnetic Y(3+) doped materials. Based on different concentration dependences of the NMR lineshape parameters, we conclude that the structural role of the Nd(3+) dopants differs significantly from that of Yb(3+). While the Nd(3+) ions appear to be statistically distributed in the PLZT lattice, incorporation of Yb(3+) into PLZT appears to be limited by the appearance of doped cubic zirconia as a secondary phase. (C) 2009 Elsevier Masson SAS. All rights reserved.

Structural and spectroscopic properties of the diazocarbene radical (CNN) and its ions CNN(+) and CNN(-): a high-level theoretical investigation

The diazocarbene radical, CNN, and the ions CNN(+) and CNN(-) were investigated at a high level of theory. Very accurate structural parameters for the states X(3)Sigma(-) and A(3)Pi of CNN, and X(2)Pi of both CNN(+) and CNN(-) were obtained with the UCCSD(T) method using correlated-consistent basis functions with extrapolations to the complete basis set limit, with valence only and also with all electrons correlated. Harmonic and anharmonic frequencies were obtained for all species and the Renner parameter and average frequencies evaluated for the Pi states. At the UCCSD(T)/CBS(T-5) level of theory, Delta(f)H(0 K) = 138.89 kcal/mol and Delta(f)H(298 K) = 139.65 kcal/mol were obtained for diazocarbene; for the ionization potential and the electron affinity of CNN, 10.969 eV (252.95 kcal/mol), and 1.743 eV (40.19 kcal/mol), respectively, are predicted. Geometry optimization was also carried out with the CASSCF/MRCI/CBS(T-5) approach for the states X(3)Sigma(-) A(3)Pi, and a(1)Delta of CNN, and with the CASSCF/MRSDCI/aug-cc-pVTZ approach for the states b(1)Sigma(+), c(1)Pi, d(1)Sigma(-), and B(3)Sigma(-), and excitation energies (T(e)) evaluated. Vertical energies were calculated for 15 electronic states, thus improving on the accuracy of the five transitions already described, and allowing for a reliable overview of a manifold of other states, which is expected to guide future spectroscopic experiments. This study corroborates the experimental assignment for the vertical transition X (3)Sigma(-) <- E (3)Pi.

Electrical and optical properties of poly(2-dodecanoylsulfanyl-p-phenylenevnylene) and its application in electroluminescent devices

We describe the optical and electrical characterization of a poly(p-phenylenevinylene) derivative: poly(2-dodecanoylsulfanyl-p-phenylenevinylene) (12COS-PPV). The electrical characterization was carried out on devices with the FTO\PEDOT:PSS\12COS-PPV/Al structure. Positive charge carrier mobility mu(h) of similar to 1.0 x 10(-6) cm(2) V(-1) s(-1) and barrier height phi of similar to 0.1 eV for positive charge carrier injection at the PEDOT:PSS/12COS-PPV interface were obtained using a thermionic injection model. FTO\PEDOT:P55\12COS-PPV/Ca devices exhibited green-yellow electroluminescence with maximum emission at lambda = 540 nm.

Structural and Electronic Properties of Dipyridamole and Derivatives

Quantum mechanical calculations at the B3LYP theory level, together with the 6-31G* basis set, were employed to obtain the energy, ionization potential, and polarizabilites for dipyridamole and derivatives, which are compared with their biological activity. Density functional calculations of the spin densities were performed for radical formed by electron abstraction of dipyridamole and derivatives. The unpaired electron remains in dipyridamole is localized on the nitrogen atoms in the substituent positions 1, 3, 5, 7, 11, 12, 13, 14, with participation of the 9 and 10 carbons in the pyrimido-pyrimidine ring. The antioxidant activity is related with ionization potential, polarizability and Log P.

Tailoring the Structural Properties of PVDF and P(VDF-TrFE) by Using Natural Polymers as Additives

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structural and electrochemical properties of LiCoO2 prepared by combustion synthesis

LiCoO2 powders were prepared by combustion synthesis, using metallic nitrates as the oxidant and metal sources and urea as fuel. A small amount of the LiCoO2 phase was obtained directly from the combustion reaction, however, a heat treatment was necessary for the phase crystallization. The heat treatment was performed at the temperature range from 400 up to 700 degreesC for 12 h. The powders were characterized by X-ray diffraction (XRD), X ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and specific surface area values were obtained by BET isotherms. Composite electrodes were prepared using a mixture of LiCoO2, carbon black and poly(vinylidene fluoride) (PVDF) in the 85:10:5% w/w ratio. The electrochemical behavior of these composites was evaluated in ethylene carbonate/dimethylcarbonate solution, using lithium perchlorate as supporting electrolyte. Cyclic voltammograms showed one reversible redox process at 4.0/3.85 V and one irreversible redox process at 3.3 V for the LiCoO2 obtained after a post-heat treatment at 400 and 500 degreesC.Raman spectroscopy showed the possible presence of LiCoO2 with cubic structure for the material obtained at 400 and 500 degreesC. This result is in agreement with X-ray data with structural refinement for the LiCoO2 powders obtained at different temperatures using the Rietveld method. Data from this method showed the coexistence of cubic LiCoO2 (spinel) and rhombohedral (layered) structures when LiCoO2 was obtained at lower temperatures (400 and 500 degreesC). The single rhombohedral structure for LiCoO2 was obtained after post-heat treatment at 600 degreesC. The maximum energy capacity in the first discharge was 136 mA g(-1) for the composite electrode based on LiCoO2 obtained after heat treatment at 700 degreesC. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Structural and optical properties of chlorinated plasma polymers

Amorphous hydrogenated chlorinated carbon (a-C:H:Cl) films were produced by the plasma polymerization of chloroform-acetylene-argon mixtures in a radiofrequency plasma enhanced chemical vapor deposition system. The main parameter of interest was the proportion of chloroform in the feed, R(C), which was varied from 0 to 80%. Deposition rates of 80 nm min (1) were typical for the chlorinated films. Infrared reflection-absorption spectroscopy revealed the presence of C-Cl groups in all the films produced with chloroform in the feed. X-ray photoelectron spectroscopy confirmed this finding, and revealed a saturation of the chlorine content at similar to 47 at.% for R(C)>= 40%. The refractive index and optical gap, E(04), of the films were roughly in the 1.6 to 1.7, and the 2.8 to 3.7 eV range. These values were calculated from transmission ultraviolet-visible-near infrared spectra. Chlorination leads to an increase in the water surface contact angle from similar to 40 degrees to similar to 77 degrees. (C) 2011 Elsevier B.V. All rights reserved.

Structural and optical properties of CaTiO3 perovskite-based materials obtained by microwave-assisted hydrothermal synthesis: An experimental and theoretical insight

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)