S. M. Zanetti

Preparation and characterization of nanosized SrBi2Nb2O9 powder by the combustion synthesis

This work presents the preparation of SrBi2Nb2O9 (SBN) directly by the combustion synthesis. Strontium nitrate, niobium ammonium oxalate (NH4H2[NbO-(C2O4)3]� 3H2O) and bismuth oxide were used as oxidant reactants and urea as fuel. The influence of the fuel was evaluated by the addition of different fuel amounts (50%, 100%, 200% and 300%), 100% being the stoichiometric proportion. The XRD patterns showed that the SBN perovskite crystallized as the majority phase. The assynthesized stoichiometric powder presented a specific surface area of around 13 m 2 /g and a mean grain size of around 16 nm. Dilatometric measurements showed that the maximum sintering rate occurs at 1275 jC. The determination of the ferroparaelectric transition showed a Curie temperature (Tc) of 429 jC. D 2002 Elsevier Science B.V. All rights reserved.

Microstructure and phase evolution of SrTiO3 thin films on Si prepared by the use of polymeric precursors

Abstract The use of polymeric precursors was employed in preparing SrTiO 3 thin films by dip coating using Si (111) as substrate. Crack free films were obtained after sintering at temperatures ranging from 550 to 1000 °C. The microstructure, characterized by SEM, shows the development of dense polycrystalline films with smooth surface and mean grain size of 52 nm, for films sintered at 1000 °C. Grazing incident angle XRD characterization of these films shows that the SrTiO 3 phase crystallizes from an inorganic amorphous matrix. No intermediate crystalline phase was identified.

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

Abstract SrBi 2 Nb 2 O 9 (SBN) thin films were prepared by the polymeric precursors method and deposited by dip coating onto Pt/Ti/SiO 2 /Si(100) substrates. The dip-coated films were specular and crack-free and crystallized during firing at 700°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 μm 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 μC/cm 2 and 100 kV/cm, respectively.

SrBi2Nb2O9 thin films deposited by dip coating using aqueous solution

A new approach for SrBi 2 Nb 2 O 9 (SBN) thin films synthesis using aqueous solution was successfully experienced. The deposition solution was prepared from Sr-Bi-Nb mixed-citrate solution, requiring no special atmosphere and using common reagents. Films were deposited by dip coating onto Pt/Ti/SiO 2 / Si(100) substrates and heat treated at temperatures ranging from 300 to 700°C. The process of formation and crystallization of SrBi 2 Nb 2 O 9 thin films, prepared by the aqueous solution method, have been studied with particular emphasis on the microstructure of crystallized films. Crystalline phases formation were followed by grazing incident X-ray diffraction (GIXRD), microstructure characterization was evaluated by scanning electron microscopy (SEM) and surface roughness were observed using atomic force microscopy (AFM). To reach the desired thickness, substrates were dipped in the deposition solution twice, forming double-layered films. The thickness of each layer ranged from 80 to 100 nm.

Superconductivity in sintered-polycrystalline PrBa2Cu3O7−δ

Abstract Superconductivity in thin films and powders, and in single crystals of PrBa 2 Cu 3 O 7− δ has been found by Blackstead et al. and Zou et al., respectively. Nevertheless, up to now it has never been reported in sintered-polycrystalline samples. We have prepared high-quality samples of this material by following a sol–gel method. We characterized the structure of all samples by using XRD and SEM-EDS techniques. Magnetic characterization was performed by measuring the magnetization as a function of temperature T , and the applied magnetic field H . Measurements were taken in the ranges 2 K K and 0 T . In this work we report for the first time superconductivity in PrBa 2 Cu 3 O 7− δ sintered-polycristalline samples, with T c around 90 K, and H c1 around 870 Oe.

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 °C to 800 °C 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 °C and 800 °C, 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 (2Pr) and coercive field (Ec) were 7.1 μC/cm2 and 113 kV/cm, and 18.8 μC/cm2 and 93 kV/cm for the films treated at 700 °C and 800 °C, respectively.

Composition control of SBN thin films deposited by PLD on various substrates

Abstract Thin films of SrBi2Nb2O9 (SBN) have been grown on both Pt/Ti/SiO2/Si and (100)MgO substrates by pulsed laser deposition. In the Sr–Bi–Nb–O system, the loss of bismuth during the process due to its volatility results obviously in a non-respect of the stoichiometry of the films and the presence of secondary phases. In order to maintain the right composition of the films, two different ways were experimented. On Pt/Ti/SiO2/Si, a sequential deposition from home-made Bi2O3 and SBN sintered targets as well as the use of Bi-enriched targets allows to obtain stoichiometric ferroelectric films. Various parameters like deposition time and periodicity of the Bi2O3 and SBN layers are of first importance. On (100)MgO which promotes SBN epitaxial growth, this sequential deposition is not suitable and we succeeded in the control of the Bi/(Sr+Nb) ratio only by using Bi-enriched targets.

Crystallization study of SrTiO3 thin films prepared by dip coating

In this study, the crystallization process of SrTiO3 thin films, prepared by a chemical method, was characterized by Fourier Transformed Infra Red (FT-IR), Grazing Incident X-ray Diffraction (GIXRD), Thermal Analysis (TG) and X-ray Absorption Near Edge Structure (XANES). The results showed that an amorphous inorganic phase is formed, consisting of clusters of oxygen five-coordinate titanium. The amorphous phase begins crystallizing at temperatures above 450 °C. No intermediate crystalline phase and no preferential orientation was observed for films deposited on MgO (100). FT-IR results suggest the presence of the carbonate group. However, the low thermal stability of this group and the low crystallization temperature of the observed SrTiO3 phase indicate that this carbonate is adsorbed.

Synthesis and characterization of bismuth zinc niobate pyrochlore nanopowders

Bismuth zinc niobate pyrochlores Bi 1.5 ZnNb 1.5 O 7 (α-BZN), and Bi 2 (Zn 1/3 Nb 2/3 ) 2 O 7 (β-BZN) have been synthesized by chemical method based on the polymeric precursors. The pyrochlore phase was investigated by differential scanning calorimetry, infrared spectroscopy, and X ray diffraction. Powder and sintered pellets morphology was examined by scanning electron microscopy. The study of α-BZN phase formation reveals that, at 500 °C, the pyrochlore phase was already present while a single-phased nanopowder was obtained after calcination at 700 °C. The crystallization mechanism of the β-BZN is quite different, occurring through the crystallization of α-BZN and BiNbO 4 intermediary phases. Both compositions yielded soft agglomerated powders. α-BZN pellets, sintered at 800 °C for 2 hours, presented a relative density of 97.3% while those of β-BZN, sintered at 900 °C for 2 hours, reached only 91.8%. Dielectric constant and dielectric loss, measured at 1 MHz, were 150 and 4 x 10 -4 for α-BZN, and 97 and 8 x 10 -4 for β-BZN.

Cracks developed during SrTiO3 thin-film preparation from polymeric precursors

Strontium titanate (SrTiO3) thin films were prepared by dip-coating Si(111) single-crystal substrates in citrate solutions of ethylene glycol, considering several citric acid/ethylene glycol (CA/EG) ratios. Measurements of intrinsic viscosity indicate that increasing the amount of EG increases the precursors’ polymeric chains and increases the weight loss. After deposition the substrates were dried on a hotplate (150 °C); this was followed by heat treatment at temperatures ranging from 500 to 700 °C using heating and cooling rates of 1 °C min ˇ1 . SEM and optical microscopy investigations of the sintered films obtained from different CA/EG ratios indicate that there is a critical thickness above which the films present cracks. This critical thickness for SrTiO3 films deposited on the Si(111) substrate is about 150 nm. Measurements of crack spacing as a function of film thickness indicate that the origin of cracks cannot be explained by the elastic behavior of the film but rather by the viscoelastic relaxation of the film during pyrolysis and sintering. Copyright # 1999 John Wiley & Sons, Ltd.