Improvement of fatigue resistance on La modified BiFeO3 thin films

A.Z. Simões,L.S. Cavalcante,C.S. Riccardi,J.A. Varela,E. Longo 한국물리학회 2009 Current Applied Physics Vol.9 No.3

The effect of lanthanum (La) addition in BiFeO3 (BFO) thin films deposited on Pt(111)/Ti/SiO2/Si(100) substrates prepared by soft chemical method was explained. Increasing La concentration promotes changes on structure, microstructure and dielectric/ferroelectric response of films. X-ray diffraction reveals that the films are free of preferred orientations and structural distortion. La addition promotes an increase in dielectric permittivity. The polarization switching and the fatigue behavior of the BFO films were significantly enhanced by the La concentration. The effect of lanthanum (La) addition in BiFeO3 (BFO) thin films deposited on Pt(111)/Ti/SiO2/Si(100) substrates prepared by soft chemical method was explained. Increasing La concentration promotes changes on structure, microstructure and dielectric/ferroelectric response of films. X-ray diffraction reveals that the films are free of preferred orientations and structural distortion. La addition promotes an increase in dielectric permittivity. The polarization switching and the fatigue behavior of the BFO films were significantly enhanced by the La concentration.

Structural and dielectric properties of polyvinyl alcohol/barium zirconium titanate polymereceramic composite

T. Badapanda,V. Senthil,S. Anwar,L.S. Cavalcante,N.C. Batista,E. Longo 한국물리학회 2013 Current Applied Physics Vol.13 No.7

The polyvinyl alcohol (PVA)/barium zirconium titanate Ba[Zr0.1Ti0.9]O3 (BZT) polymereceramic composites with different volume percentage are obtained from solution mixing and hot-pressing method. Their structural and electrical properties are characterized by X-ray diffraction (XRD), Rietveld refinement,cluster modeling, scanning electron microscope and dielectric study. XRD patterns of PVA/BZT polymereceramics composite (with 50% volume fractions) indicate no obvious differences than the XRD patterns of pure BZT which shows that the crystal structure is still stable in the composite. The scanning electron micrograph indicates that the BZT ceramic is dispersed homogeneously in the polymer matrix without agglomeration. The dielectric permittivity (εr) and the dielectric loss (tan d) of the composites increase with the increase of the volume fraction of BZT ceramic. Theoretical models are employed to rationalize the dielectric behavior of the polymer composites. The dielectric properties of the composites display good stability within a wide range of temperature and frequency. The excellent dielectric properties of these polymereceramic composites indicate that the BZT/PVA composites can be a candidate for embedded capacitors.

Structural refinement, optical and ferroelectric properties of microcrystalline Ba(Zr0.05Ti0.95)O3 perovskite

T. Badapanda,S. Sarangi,B. Behera,P.K. Sahoo,S. Anwar,T. P. Sinha,G.E. Luz Jr.,E. Longo,L.S. Cavalcante 한국물리학회 2014 Current Applied Physics Vol.14 No.5

For this study, a microcrystalline Ba(Zr0.05Ti0.95)O3 (BZT) powder was prepared by a high energy ball milling method followed by calcination at 1100 C for 4 h. The calcined powder was structurally characterized by X-ray diffraction and Rietveld refinement data, which showed that this material has a perovskite-type tetragonal structure with a space group of (P4mmm). The micro-Raman spectrum revealed local lattice distortions due to distorted octahedral [TiO6] clusters. The temperature and frequency-dependent dielectric study of the BZT ceramic showed normal phase transition behavior. The ferroelectric property was studied by a PeE hysteresis loop. Optical band gap was investigated by ultravioletevisible (UVevis) absorption spectroscopy at room temperature. The UVevis spectrum indicated that the BZT powder has an optical band gap of 3.15 eV.

Room temperature photoluminescence of BCT prepared by Complex Polymerization Method

F.V. Motta,A.P.A. Marques,J.W.M. Espinosa,P.S. Pizani,E. Longo,J.A. Varela 한국물리학회 2010 Current Applied Physics Vol.10 No.1

It was used the Complex Polymerization Method to synthesize barium calcium titanate powders (BCT). Crystalline Ba0.8Ca0.2TiO3 perovskite-type phase could be identified by X-ray diffraction and confirmed by Raman spectroscopy in the powders heat treated at 600 C. Inherent defects, linked to structural disorder,facilitate the photoluminescence emission. The photoluminescent emission peak maximum was around of 533 nm (2.33 eV) for the Ba0.8Ca0.2TiO3. The photoluminescence process and the band emission energy photon showed dependence of both the structural order–disorder and the thermal treatment history. The results revealed that Ba0.8Ca0.2TiO3 (BCT20) is a highly promising candidate material for optical applications.

Electronic Structure, Morphological Aspects, Optical and Electrochemical Properties of RuO2 Nanocrystals

R. C. Silva,A. F. Gouveia,J. C. Sczancoski,R. S. Santos,J. L. S. Sá,E. Longo,L. S. Cavalcante 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.5

This letter reports the synthesis of RuO2nanocrystals by the anionic surfactant-assisted hydrothermal method at 90 °C for24 h followed by heat treatment at 500 °C for 1 h. These crystals were structurally characterized by means of X-ray diffraction(XRD) and Rietveld refinement analysis. Field emission scanning electron microscopy (FE-SEM) was employed to observethe morphological features these crystals. The optical behavior was investigated by ultraviolet–visible (UV–Vis) spectroscopy. First-principles quantum mechanical calculations based on the density functional theory at the B3LYP level wereemployed to obtain the electronic band structure and density of states. For electrochemical behavior, the supercapacitorproperties of RuO2crystals were investigated by cyclic voltammetry. XRD patterns and Rietveld refinement data indicatethat RuO2crystals have a rutile-type tetragonal structure. FE-SEM images showed the presence of sphere-like RuO2crystalswith an average crystal sized at around 19.13 nm. The experimental band gap energy (Egap[exp]) was estimated at 2.60 eV byusing UV–Vis spectroscopy, while the theoretical calculations indicate an Egap[theo] at 1.92 eV. These calculations revealed aband structure predominantly composed of O 2p orbitals (valence band) and Ru 4d orbitals (conduction band). The specificcapacitance measured for RuO2film was 193 F g−1 at 5 mV s−1 in an electrode with 0.5 mg of electroactive material in 1 MNa2SO4solution.

Rietveld refinement, microstructure, conductivity and impedance properties of Ba[Zr_0.25Ti_0.75]O_3 ceramic

T. Badapanda,V. Senthil,S.K. Rout,L.S. Cavalcante,A.Z. Simões,T. P. Sinha,S. Panigrahi,M.M. de Jesus,E. Longo,J.A. Varela 한국물리학회 2011 Current Applied Physics Vol.11 No.6

In this work, we report the Rietveld refinement, microstructure, conductivity and impedance properties of Ba[Zr_0.25Ti_0.75]O_3 ceramic synthesized by solid state reaction. This ceramic was characterized by X-ray diffraction, Rietveld refinement, scanning electron microscopy and energy dispersive X-ray spectrometry. Impedance spectroscopy analyses reveals a non-Debye relaxation phenomenon being its relaxation frequency moving toward to positive side with increase of temperature. A significant shift in impedance loss peaks toward higher frequency side indicates conduction in material and favoring the long range motion of mobile charge carriers. The frequency dependent ac conductivity at different temperatures indicates that the conduction process is thermally activated. The variation of dc conductivity exhibited a negative temperature coefficient of resistance behavior. The ac conductivity data are used to evaluate the density of states at Fermi level and activation energy of this ceramic. The dc electrical and thermal conductivities of grain and grain boundary have been discussed.

Electronic structure and optical properties of BaMoO4 powders

J.C. Sczancoski,L.S. Cavalcante,N.L. Marana,R.O. da Silva,R.L. Tranquilin,M.R. Joya,P.S. Pizani,J.A. Varela,J.R. Sambrano,M. Siu Li,E. Longo,J. Andrés 한국물리학회 2010 Current Applied Physics Vol.10 No.2

Barium molybdate (BaMoO4) powders were synthesized by the co-precipitation method and processed in microwave-hydrothermal at 140 ℃ for different times. These powders were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), ultraviolet–visible (UV–vis) absorption spectroscopies and photoluminescence (PL) measurements. XRD patterns and FT-Raman spectra showed that these powders present a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a large absorption band situated at around 850.4 cm1, which is associated to the Mo–O antisymmetric stretching vibrations into the [MoO4] clusters. UV–vis absorption spectra indicated a reduction in the intermediary energy levels within band gap with the processing time evolution. First-principles quantum mechanical calculations based on the density functional theory were employed in order to understand the electronic structure (band structure and density of states) of this material. The powders when excited with different wavelengths (350 nm and 488 nm) presented variations. This phenomenon was explained through a model based in the presence of intermediary energy levels (deep and shallow holes) within the band gap.