Dielectric Spectroscopy Analyses of SrBi4Ti4O15 Films Obtained from Soft Chemical Solution

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

Vortex lattice of a long superconducting wire with a columnar defect

In the present work we study a long superconducting wire with a columnar defect in the presence of an applied magnetic field. The cross section of the cylinder is assumed to be circular. The field is taken uniform and parallel to the cylinder axis. We use the London theory to investigate the vortex lattice inside the wire. Although this theory is valid in the limit of low vortex density, that is, when the nearest neighbor vortex distance is much larger than the coherence length, we can obtain a reasonable qualitative description of lattice properties. We calculate: (1) the vortex lattice structure using the simulated annealing technique; (2) the magnetization curve as a function of the applied field.

Depairing critical current density of a mesoscopic square superconductor

In the present paper we consider the vortex lattice properties of a square superconductor such as the vortex patterns, the Gibbs free energy, the magnetization, and the depairing critical current density. We show that this last quantity shows a matching effect, that is, it shows a discontinuous behavior as a function of the applied magnetic field.

Magnetic properties of Cu1+xMn2-xO4 and Ni1+xMn2-xO4 solid solutions

Magnetic properties of two spinel oxides solid solutions, Cul+xMn2-xO4 and Ni1+xMn2-xO4 are reported. These series are characterized by two magnetic transitions: the upper one, of ferrimagnetic type, occurs at about 85 K (for copper-based) and at 105-110 K (for nickel-based spinels), independently of the x-content: the lower transition may be related to a Neel-type collinear ordering and takes place at 30 and 45 K, respectively. Application of moderate fields (H > 250 Oe) make both transitions to merge into one broad maximum in the magnetization, which takes place at lower temperature when applying larger fields. Magnetization cycles with temperature (ZFC/FC) or field (loops) allowed us to well characterize the ordered state. The effective moment follows the expected behavior when manganese ions are being substituted by ions of lower magnetic moment (Ni(2+)andCU(2+)). (c) 2007 Elsevier Ltd. All rights reserved.

Piezoelectric behaviour of PZT doped with calcium: A combined experimental and theoretical study

An experimental and theoretical study on the piezoelectric behaviour of PZT doped with a range of calcium ion concentrations is presented. A systematic study of the effect on the piezoelectric properties of PZT doped with various concentrations of CaO at constant sintering temperature and sintering time was carried out. The remanent polarization, planar coupling factor and frequency-thickness constant increase with calcium concentration. Ab initio perturbed ion calculations show that the lattice energy decreases with calcium addition for both tetragonal and rhombohedral phases of PZT.

Ferroelectric and microstructural characteristics of SrBi2Ta2O9 thin films crystallized by the rapid thermal annealing process

Ferroelectric SrBi2Ta2O9 thin films on Pt/Ti/SiO2/Si were successfully synthesized by the modified polymeric precursor method. The films were deposited by spin coating and crystallized by rapid thermal annealing in a halogen lamp furnace, followed by postannealing at temperatures ranging from 700 degreesC to 800 degreesC in an oxygen atmosphere. Microstructural and phase evaluations were followed by x-ray diffraction and atomic force microscopy. The films displayed spherical grain structures with a superficial roughness of approximately 3-6 nm. The dielectric constant values were 121 and 248 for films treated at 700 degreesC and 800 degreesC, respectively. The P-E curve showed a voltage shift toward the positive side, which was attributed to crystallization under the halogen illumination. The remanent polarization (2P(r)) and coercive field (E-c) were 7.1 muC/cm(2) and 113 kV/cm, and 18.8 muC/cm(2) and 93 kV/cm for the films treated at 700 degreesC and 800 degreesC, respectively. (C) 2001 American Institute of Physics.

Magnetic properties of acicular ultrafine iron particles

Magnetic properties of acicular (similar to60 and similar to200 nm) iron particles, obtained by reduction of alumina-coated goethite particles, are reported. X-ray diffraction and Mossbauer spectroscopy showed that the particles consist of a alpha-Fe core and a thin surface layer of maghemite. Magnetization data indicated an improvement of similar to28% in the saturation magnetization, coercive field, and squareness for particles with similar to60 nm. This magnetic property enhancement of the present particles, whose size is 40% smaller than those commercially available, could result in a similar decrease of the bit-size for higher density of magnetic media.

Soft chemical deposition of BiFeO3 multiferroic thin films

BiFeO3 thin films free of secondary phases were obtained by the soft chemical solution on Pt(111)/Ti/SiO2/Si substrates after annealing at 500 degrees C for 2 h. The film grown in the (100) direction presented a remanent polarization P-r of 31 mu C/cm(2) at room temperature. Electrical measurements using both quasistatic hysteresis and pulsed polarization confirm the existence of ferroelectricity with a switched polarization of 60-70 mu C/cm(2), Delta P=(P-*-P). Low leakage conduction and an out-of-plane piezoelectric (d(3)) coefficient of 40 pm/V were obtained by the improvement of preparation technology.

Temperature-dependent vortex motion in a square mesoscopic superconducting cylinder: Ginzburg-Landau calculations

In this work we investigate the dynamics of vortices in a square mesoscopic superconductor. As time evolves we show how the vortices are nucleated into the sample to form a multivortex, single vortex, and giant vortex states. We illustrate how the vortices move around at the transition fields before they accommodate into an equilibrium configuration. We also calculate the magnetization and the free energy as functions of the applied magnetic field for several values of temperature. In addition, we evaluate the upper critical field.

Microstructural, dielectric and ferroelectric properties of calcium-modified lead titanate thin films derived by chemical processes

Ferroelectric Pb1-xCaxTiO3 (x = 0.24) thin films were formed on a Pt/Ti/SiO2/Si substrate by the polymeric precursor method using the dip-coating technique for their deposition. Characterization of the films bq X-ray diffraction showed a perovskite single phase with a tetragonal structure after annealing at 700 degreesC. Atomic force microscopy (AFM) analyses showed that the film had a smooth and crack-free surface with low surface roughness. In addition, the PCT thin film had a granular structure with an 80 nm grain size. The thickness of the films observed by the scanning electron microscopy (SEM) is 550 nm and there is a good adhesion between the film and substrate. For the electrical measurements metal-ferroelectric-metal of the type capacitors were obtained, where the thin films showed good dielectric and ferroelectric properties. The dielectric constant and dissipation factor at 1 kHz and measured at room temperature were found to be 457 and 0.03. respectively. The remanent polarization and coercive field for the: deposited films were P-r = 17 muC/cm(2) and E-c = 75 kV/cm, respectively. Moreover. The 550-nm-thick film showed a current density in the order of 10(-8) A/cm(2) at the applied voltage of 2 V. The high values of the thin film's dielectric properties are attributed to its excellent microstructural quality and the chemical homogeneity obtained by the polymeric precursor method. (C) 2001 Elsevier science Ltd. All rights reserved.

Improvement of the dielectric and ferroelectric properties in superlattice structure of Pb(Zr,Ti)O-3 thin films grown by a chemical solution route

Making heterolayered perovskite materials constitutes an approach for the creation of better dielectric and ferroelectric properties. In the experiment reported here, heterolayered PZT40/PZT60 films were grown on Pt/Ti/SiO2/Si (100) by a chemical solution deposition. The dielectric constant of the heterolayered thin film was significantly enhanced compared with that of pure PZT40 and PZT60 thin films. A dielectric constant of 701 at 100 kHz was observed for a stacking periodicity of six layers having a total thickness of 150 nm. The heterolayered film exhibited greater remanent polarization than PZT60 and PZT40 films. The values of remanent polarization were 7.9, 18.5, and 31 muC/cm(2), respectively, for pure PZT60, PZT40, and heterolayered thin films, suggesting that the superior dielectric and ferroelectric properties of the heterolayered thin film resulted from a cooperative interaction between the ferroelectric phases made from alternating tetragonal and rhombohedral phases of PZT, simulating the morphotropic phase boundary of this system. (C) 2004 American Institute of Physics.

Preparation and properties of ferroelectric Pb1-xCaxTiO3 thin films produced by the polymeric precursor method

Pb1- xCaxTiO3 thin films with x = 0.24 composition were prepared by the polymeric precursor method on Pt/Ti/SiO2/Si substrates. The surface morphology and crystal structure, and the ferroelectric and dielectric properties of the films were investigated. X-ray diffraction patterns of the films revealed their polycrystalline nature. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness. The multilayer Pb1-xCaxTO3 thin films were granular in structure with a grain size of approximately 60-70 nm. The dielectric constant and dissipation factor were, respectively, 174 and 0.04 at a 1 kHz frequency. The 600-nm thick film showed a current density leakage in the order of 10(-7) A/cm(2) in an electric field of about 51 kV/cm. The C-V characteristics of perovskite thin films showed normal ferroelectric behavior. The remanent polarization and coercive field for the deposited films were 15 muC/cm(2) and 150 kV/cm, respectively. (C) 2001 Kluwer Academic Publishers.

Structural and electrical properties of SrBi2Nb2O9 thin films prepared by chemical aqueous solution at low temperature

SrBi2Nb2O9 (SBN) thin films were prepared by the polymeric precursors method and deposited by dip coating onto Pt/Ti/SiO2/Si(100) substrates. The dip-coated films were specular and crack-free and crystallized during firing at 700 degrees C. Microstructure and morphological evaluation were followed by grazing incident X-ray diffraction (GIXRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The films exhibited somewhat porous grain structure with rounded grains of about 100 nm. For the electrical measurements, gold electrodes of 300 mu m in diameter were sputter deposited on the top surface, forming a metal-ferroelectric-metal (MFM) configuration. The remanent polarization (P-r) and coercive field (E-c) were 5.6 mu C/cm(2) and 100 kV/cm, respectively. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Composites PVDF-TrFE/BT used as bioactive membranes for enhancing bone regeneration

In this paper a piezoelectric composite membranes were developed for charge generator to promoter bone regeneration on defects sites. Is known that the osteogenesis process is induced by interactions between biological mechanisms and electrical phenomena. The membranes were prepared by mixing Barium Titanate (BT) powders and PVDF-TrFE (PVDF:TrFE = 60:40 mol%) on dimethylformamide medium. This precursor solution was dried and crystallized at 100degreesC for 12 hours. Composites membranes were obtained by following methods: solvent casting (SC), spincoating (SP), solvent extraction by water addition (WS) and hot pressing (HP).The microstructural analysis performed by SEM showed connectivity type 3-0 and 3-1 with high homogeneity for samples of ceramic volume fraction major than 0.50. Powder agglomerates within the polymer matrix was evidenced were observed for composites with the BT volume fraction major than 40%. The composite of ceramic fraction of 0.55 presented the best values of remanent polarization (similar to33 muC/cm(2)), but the flexibility of these composites with the larger ceramic fraction was significantly affected.For in vivo evaluation PVDF-TrFE/BT 90/10 membranes with 3cm larger were longitudinally implanted under tibiae of male rabbit. After 21 days the animals were sacrificed. By histological analyses were observed neo formed bone with a high mitotic activity. In the interface bone-membrane was evidenced a pronounced callus formation. These results encourage further applications of these membranes in bone-repair process.

Ferroelectric and piezoelectric properties of bismuth titanate thin films grown on different bottom electrodes by soft chemical solution and microwave annealing

Bismuth titanate (Bi4Ti3O12, BIT) films were evaluated for use as lead-free piezoelectric thin films in micro-electromechanical systems. The films were grown by the polymeric precursor method on LaNiO3/SiO2/Si (1 0 0) (LNO), RuO2/SiO2/Si (1 0 0) (RuO2) and Pt/Ti/SiO2/Si (1 0 0) (Pt) bottom electrodes in a microwave furnace at 700 degrees C for 10 min. The domain structure was investigated by piezoresponse force microscopy (PFM). Although the converse piezoelectric coefficient, d(33), regardless of bottom electrode is around (similar to 40 pm/V), those over RuO2 and LNO exhibit better ferroelectric properties, higher remanent polarization (15 and 10 mu C/cm(2)), lower drive voltages (2.6 and 1.3 V) and are fatigue-free. The experimental results demonstrated that the combination of the polymeric precursor method assisted with a microwave furnace is a promising technique to obtain films with good qualities for applications in ferroelectric and piezoelectric devices. (c) 2006 Elsevier Ltd. All rights reserved.