Augusto Celso Antunes

Electric and morphologic properties of SnO2 films prepared by modified sol–gel process

Abstract Tin dioxide (SnO 2 ) is used in several technological applications such as sensors, catalysts, and electro-optical equipments. Many of these applications involve the use of SnO 2 in the form of ceramic thin film. The preparation of SnO 2 films has been widely studied and different methods have been proposed to synthesize pure or doped SnO 2 . In this work, SnO 2 films produced by the modified sol–gel method, using tin tartrate as a precursor, are presented. The sol stability was verified using UV–visible spectroscopy. The obtained films were characterized by X-ray diffraction (XRD), optical microscopy, electrical measurements, scanning electron microscopy (SEM), and X-ray fluorescence (FRX). The obtained films presented a thickness of 0.3 μm and an amorphous structure. The sensor electrical sensibility at 300 °C in the presence of LPG was clearly shown.

Effect of Fe2O3 doping on the electrical properties of a SnO2 based varistor

The effect of Fe2O3 addition on the densification and electrical properties of the (0.9895 − x) SnO2 + 0.01CoO + 0.005Nb2O5 + xFe2O3 system, where x = 0.005 or 0.01, was considered in this study. The samples were sintered at 1300°C for 2 h. Microstructure analysis by scanning electron microscopy showed that the effect of Fe2O3 addition is to decrease the SnO2 grain size. J × E curves indicated that the system exhibit a varistor behavior and the effect of Fe2O3 is to increase both, the non-linear coefficient (α) and the breakdown voltage (Er). Considering the Schottky thermionic emission model the potential height and width were estimated. Small amount addition of Fe2O3 to the basic system increases both the potential barrier height and width.

Effect of La2O3 doping on the microstructure and electrical properties of a SnO2-based varistor

The effect of La2O3 addition on the densification and electrical properties of the (0.9895-xSnO2+0.01CoO+0.0005Nb2O5+x La2O5 system, where x=0.0005 or 0.00075, was considered in this study. The samples were sintered at 1300 °C for 2 and 4 h and a single SnO2 phase was identified by X-ray diffraction. Microstructure analysis by scanning electron microscopy showed that the affect of La2O3 addition is to decrease the SnO2 grain size. J versus E curves indicated that the system exhibits a varistor behavior and the effect of La2O3 is to increase both the non-linear coefficient (α) and the breakdown voltage (E2). Considering the Schottky thermionic emission model the potential height and the width were estimated. The addition of small amounts of La2O3 to the basic system increases the potential barrier height and decreases both grain size and potential barrier width.

Effect of Ta2O5 doping on the electrical properties of 0.99SnO2·0.01CoO ceramic

The effect of Ta2O5 doping in 0.99SnO2·0.01CoO on the microstructure and electrical properties of this ceramic were analyzed in this study. The grain size was found to decrease from 6.87 μm to 5.68 μm when the Ta2O5 concentration increased from 0.050 to 0.075 mol%. DC electrical characterization showed a dramatic increase in the current loss and decrease in the non-linear coefficient with the increase of the Ta2O5 concentration. The conduction mechanism is by thermionic emission and the potential barriers are of Schottky type, separated by a thin film.

MNDO theoretical study of ethanol decomposition process on SnO2 surfaces

Abstract An MNDO study has been carried out to analyze the decomposition process of the ethanol molecule on a SnO 2 surface. A (SnO 2 ) 7 (110) model has been selected to represent the surface. The decomposition process has been monitored by selection of a hydrogen-α-carbon distance of the ethanol molecule as reaction coordinate. This minimum energy profile shows a maximum of 186 kJ mol -1 , and in the transition state there is a transfer of hydrogen-α-carbon to the SnO 2 surface. There is also the interaction between the alcohol hydroxyls and the two oxygens of the oxide.

Influência do Método de Obtenção de Partículas de Nb 2 O 5 Empregadas em Células Solares Sensibilizadas por Corante Compostas de TiO 2 /Nb 2 O 5

The niobium pentoxide (Nb 2 O 5 ) is a semiconductor capable of prevent the efficiency loss by recombination in dye sensitized solar cells (DSSC) given the high energy gap. The aim of this study is to investigate the performance of DSSC containing Nb 2 O 5 obtained by Pechini method and hydrothermal synthesis, mixed with TiO 2 nanoparticles. The characterization techniques used were X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DSL) and potentiodynamic polarization under power light incidence of 100 mWcm -2 . XRD confirmed obtaining orthorhombic structure niobium pentoxide tested for both methodologies, the SEM showed the best distribution of the oxide obtained by hydrothermal synthesis efficiency was calculated from the current density-potential curves (j-v) confirming the higher efficiency for this sample, about 20% higher. DOI: 10.5935/1984-6835.20160064

Biocerâmicas aditivadas com nióbio (V): avaliação da rota hidrotérmica modificada com ácido cítrico e ureia para obtenção de hidroxiapatitas modificadas

Synthetic hydroxyapatite (Ca10(PO4)6(OH)2; HA) has become a widely used ceramic material for bone reconstruction due to its biocompatibility with the bone tissue. This biocompatibility as well as other physical and chemical properties of the hydroxyapatite can be modified by the addition of different ions to its structure. Niobium (V) ion has not been commonly used in the hydroxyapatite synthesis. The objective of this study was to evaluate the use of hydrothermal route in the niobium (V) doped hydroxyapatite synthesis. The route used the niobium ammonium oxalate (NH4H2[NbO(C2O4)3].3H2O) complex as a niobium (V) ion precursor. The addition of citric acid and urea in the hydrothermal route is used for the control of synthesis pH and precipitation rate. Pure sample and sample added with 5.3 ppm of niobium (V) ion were prepared. The coexistence of other phases besides the hydroxyapatite was not observed in any of the samples through the use of X-ray diffraction and infrared spectroscopy (FTIR) techniques. The FTIR technique revealed the presence of hydroxyapatite characteristic functional groups. The scanning electron microscopy analysis showed the formation of agglomerates composed of round particles, confirmed by the transmission electron microscopy technique. The X-ray fluorescence spectroscopic analysis detected the presence of niobium in the doped sample. The results showed that niobium (V) doped hydroxyapatite can be synthesized by means of hydrothermal route, which may be considered as huge potential for future application in bioceramics.