LiNbO3 thin films prepared from a polymeric precursor method

LiNbO3 thin films were prepared from polymeric precursor method by dip coating. The precursor films, deposited on Si(111) substrates, were heat-treated from 400°C to 900°C in order to study the heat treatment influence on the crystallinity and microstructure of the final film. The X-ray diffraction patterns showed, in particular, that these films crystallize at low temperature (450°C) and present no preferential orientation. The scanning electron microscopy studies showed that the film microstructure is strongly influenced by the annealing temperature. © 1997 Trans Tech Publications.

Synthesis of PbTiO3 by use of polymeric precursors

Lead titanate powders were synthesized through the use of polymeric precursors according to the Pechini Process. The polymeric precursor was calcined at temperatures ranging from 300 to 600°C for 1 or 2 h. X-ray diffraction (XRD) showed that lead titanate crystallizes from the precursor at temperatures as low as 400°C. No intermediate carbonate phase was detected by Fourier transform infrared spectroscopy (FTIR) or by XRD. A powder with mean particle size of 150 nm was obtained after calcination of the precursor at 600°C for 1 h. © 1998 Elsevier Science B.V. All rights reserved.

Preparation and characterization of SrBi2Nb2O9 thin films made by polymeric precursors

A polymeric precursor solution was employed in preparing SrBi2Nb2O9 (SBN) powder and thin films dip coated onto Si(100) substrate. XRD results show that the SBN perovskite phase forms at temperatures as low as 600°C through an intermediate fluorite phase. This fluorite phase is observed for samples heat-treated at temperatures of 400 and 500°C. After heat treatment at temperatures ranging from 300 to 800°C, thin films were shown to be crack free. Grazing incident angle XRD characterization shows the occurrence of the fluorite intermediate phase for films also. The thickness of films, measured by MEV, was in the order of 80-100 nm.

Structural and surface morphology characterizations of oriented LiNbO3 thin films grown by polymeric precursor method

Polymeric precursor solution was used to deposit LiNbO3 thin films by dip coating on sapphire substrates. The effects of processing variables, such as heat treatment conditions and number of deposited layers, on crystallinity and morphology of the final films were investigated. X-ray diffraction patterns show the oriented growth of the films. The rocking curves, obtained around the (006) LiNbO3 peak, revealed that the shape peak and the FWHM value were influenced by the processing variables. According to these parameters, some films presented very homogeneous dense and smooth surfaces, as shown by the SEM and AFM studies.

Influence of heat treatment on LiNbO3 thin films prepared on Si(111) by the polymeric precursor method

The effects of heat-treatment temperature on LiNbO3 thin films prepared by the polymeric precursor method were investigated. The precursor solution was deposited on Si(111) substrates by dip coating. X-ray diffraction and thermal analyses revealed that the crystallization process occurred at a low temperature (420 °C) and led to films with no preferential orientation. High-temperature treatments promoted formation of the LiNb3O8 phase. Scanning electron microscopy, coupled with energy dispersive spectroscopy analyses, showed that the treatment temperature also affected the film microstructure. The surface texture - homogeneous, smooth, and pore-free at low temperature - turned into an `islandlike' microstructure for high-temperature treatments.

Preparation and properties of ferroelectric BaTiO3 thin films produced by the polymeric precursor method

Ferroelectric barium titanate thin films were produced by the polymeric precursor method. In this technique, the desired metal cations are chelated in a solution using a hydroxycarboxylic acid as the chelating agent. Barium carbonate and titanium IV isopropoxide were used as precursors for the citrate solution. Ethylene glycol and citric acid were used as polymerization/complexation agents for the process. The crystalline structure of the film annealed at 700 °C had a single perovskite phase with a tetragonal structure. The BaTiO3 film showed good P-E hysteresis loops and C-V characteristics due to the switched ferroelectric domains.

Preparation and characterization of BaBi2Nb2O9(BBN) ceramics synthetized by polymeric precursors method

Pure BBN powders and with addition of 1 and 2 wt% in excess of bismuth were obtained by Pechini Method. The powders calcined at 300°C/4h were analyzed by TG/DTA to study the temperature of organic matter decomposition. A systematic study of calcination temperature and time to the formation of the BBN phase was performed and the phase formation was accompanied by XRD. The calcined powders at 800°C during 2h were analyzed by infrared spectroscopy and by BET. The powders were isostaticaly pressed and sintered at temperatures ranging from 900°C to 1000°C. The ceramics were characterized by XRD to control the crystalline phase and by SEM to analyze the microstructure.

Effect of thermal treatment on the morphology of PLZT thin films prepared from polymeric precursor method

Lead lanthanum zirconate titanate (PLZT) thin films with (9/65/35) stoichiometry were prepared by dip coating from polymeric precursor method. The films deposited on silicon (100) substrates, were thermally treated from 450° to 700°C for 6 hours in order to study the influence of thermal treatment on the crystallinity, microstructure, grain size and roughness of the final film. X-ray diffraction results showed that PLZT phase crystallizes at low temperature (500°C) and present preferential orientation. It was observed by scanning electron microscopy (SEM) that it is possible to obtain dense thin films at temperatures around 650°C. The atomic force microscopy (AFM) studies showed that the grain size and roughness are strongly influenced by the annealing temperature.

Influence of barium and strontium addition on the ratio c/a of PZT obtained by the polymeric precursor method

Lead zirconate titanate powder, with Zr/Ti ratio of 50/50 was prepared by Pechini method after adding up to 10,0 mol% of Ba +2 and Sr +2 ions. Tetragonal phase is favored by the increase of barium and strontium concentration in the LiNbO 3 crystal lattice. The ratio c/a for tetragonal phase increases with the content of Ba +2 and Sr +2.

Crystallographic, dielectric and optical properties of SrBi 2Ta2O9 thin films prepared by the polymeric precursor method

Strontium bismuth tantalate thin films were prepared on several substrates (platinized silicon (Pt/Ti/SiO 2 /Si), n -type (100)-oriented and p -type (111)-oriented silicon wafers, and fused silica) by the solution deposition method. The resin was obtained by the polymeric precursor method, based on the Pechini process, using strontium carbonate, bismuth oxide, and tantalum ethoxide as starting reagents. Characterizations by XRD and SEM were performed for structural and microstructural evaluations. The electrical measurements, carried on the MFM configuration, showed P r values of 6.24 μC/cm 2 and 31.5 kV/cm for the film annealed at 800 C. The film deposited onto fused silica and treated at 700 C presented around 80% of transmittance. © 2002 Taylor & Francis.

Effect of magnesium on the properties of LiNbO 3 thin films prepared from polymeric precursors

The effect of magnesium addition on the phase formation, microstructure and electric and ferroelectric properties of LiNbO 3 thin films prepared through polymeric precursors was analyzed. By X ray diffraction no secondary phase was observed with the increase of magnesium concentration. Comparing to pure LiNbO 3, the addition of 0.5 and 1.0 mol% of Mg +2 increased of the dielectric constant, while 2.0 mol% decreased it. It was noticed that the increase in additive concentration decreases the ferroelectric remanent polarization and increases the coercive field. © 2002 Taylor & Francis.

Microstructure of doped barium titanate prepared from polymeric precursors

Barium titanate is used extensively as a dielectric in ceramic capacitors, particularly due to its high dielectric constant and low dielectric loss characteristics. It can be made semiconducting by addition of certain dopants and by proper modification of grains and grain boundary properties obtaining very interesting characteristics for various applications. The synthesis method and sintering regime have a strong influence on properties of obtained barium titanate ceramics. Doped barium titanate was prepared with Nb+5 and Y+3 ions as donor dopants, and with Mn+2 ions as acceptor dopant by polymeric precursors method. By this procedure nanosized powders were obtained after calcination. Sintering was performed in the temperature range of 1290°C to 1380°C The microstructure of doped BaTiO3 was performed using scanning electron microscopy. The influence of dopants and sintering temperature on grain size was analysed.

Different doses of exogenous surfactant for treatment of meconium aspiration syndrome in newborn rabbits.

OBJECTIVE: To evaluate the effects of 2 different doses of exogenous surfactant on pulmonary mechanics and on the regularity of pulmonary parenchyma inflation in newborn rabbits. METHOD: Newborn rabbits were submitted to tracheostomy and randomized into 4 study groups: the Control group did not receive any material inside the trachea; the MEC group was instilled with meconium, without surfactant treatment; the S100 and S200 groups were instilled with meconium and were treated with 100 and 200 mg/kg of exogenous surfactant (produced by Instituto Butantan) respectively. Animals from the 4 groups were mechanically ventilated during a 25-minute period. Dynamic compliance, ventilatory pressure, tidal volume, and maximum lung volume (P-V curve) were evaluated. Histological analysis was conducted using the mean linear intercept (Lm), and the lung tissue distortion index (SDI) was derived from the standard deviation of the means of the Lm. One-way analysis of variance was used with a = 0.05. RESULTS: After 25 minutes of ventilation, dynamic compliance (mL/cm H2O.kg) was 0.87 +/- 0.07 (Control); 0.49 +/- 0.04 (MEC*); 0.67 +/- 0.06 (S100); and 0.67 +/- 0.08 (S200), and ventilatory pressure (cm H2O) was 9.0 +/- 0.9 (Control); 16.5 +/- 1.7 (MEC*); 12.4 +/- 1.1 (S100); and 12.1 +/- 1.5 (S200). Both treated groups had lower Lm values and more homogeneity in the lung parenchyma compared to the MEC group: SDI = 7.5 +/- 1.9 (Control); 11.3 +/- 2.5 (MEC*), 5.8 +/- 1.9 (S100); and 6.7 +/- 1.7 (S200) (*P < 0.05 versus all the other groups). CONCLUSIONS: Animals treated with surfactant showed significant improvement in pulmonary mechanics and more regularity of the lung parenchyma in comparison to untreated animals. There was no difference in results after treatment with either of the doses used.

On the specific filtration mechanism of a mesoporous silica membrane, prepared with non-connecting parallel pores

We report the singular filtration properties of an ultrafiltration membrane made with mesoporous silica that exhibits cylindrical pores aligned mostly normal to the support. This membrane supported on tubular commercial macroporous alumina supports was prepared by the interfacial growth mechanism between stable silica-surfactant hybrid micelles made of the association of silica oligomers with polyethyleneoxide-based (PEO) surfactants and sodium fluoride, a well-known silica condensation catalyst [Boissière et al., An ultrafiltration membrane made with mesoporous MSU-X silica, Chem. Mater. 15 (2003) 460-463]. It appears that the combined effect of the silica nature of the membrane, whose surface charge can be easily adjusted by changing the pH and the non-connected cylindrical shape of the pores provides a new behavior in the retention properties, as proved by the filtration of polyoxyethylene polymers (PEO) with different molecular weights. Depending on the filtration conditions, a rejection rate of 80% and a steep cut-off at 2000 Da can be obtained or, on the reverse, polymers three times bigger than the pore diameter can diffuse through the membrane. This new filtration mechanism, which opens up new modes of separation modes, is explained in the light of both topology of the porous network and pH-dependent interactions between PEO polymers and silica porous media. © 2004 Elsevier B.V. All rights reserved.

Physical characterization of K-doped 0.9PMN-0.1PT synthesized by an association of the columbite route and the polymeric precursor method

The solid solution 0.9PbMg 1/3Nb 2/3O 3-0.1PbTiO 3 is one of the most widely investigated relaxor ceramic, because of its high dielectric constant and low sintering temperatures. PMN-PT powders containing single perovskite phase were prepared by using a Timodified columbite precursor obtained by the polymeric precursor method. Such precursor reacts directly with stoichiometric amount of PbO to obtain pyrochlore-free PMN-PT powders. The structural effects of K additive included in the columbite precursor and 0.9PMN-0.1PT powders were also studied. The phase formation at each processing step was verified by XRD analysis, being these results used for the structural refinement by the Rietveld method. It was verified the addition of K in the columbite precursor promotes a slight increasing in the powder crystallinity. There was not a decrease in the amount of perovskite phase PMN-PT for 1mol% of K, and the particle and grain size were reduced, making this additive a powerful tool for grain size control.