Grain size effect on the electrical response of SnO2 thin and thick film gas sensors

Porous nano and micro crystalline tin oxide films were deposited by RF Magnetron Sputtering and doctor blade techniques, respectively. Electrical resistance and impedance spectroscopy measurements, as a function of temperature and atmosphere, were performed in order to determine the influence of the microstructure and working conditions over the electrical response of the sensors. The conductivity of all samples increases with the temperature and decreases in oxygen, as expected for an n-type semiconducting material. The impedance plots indicated the existence of two time constants related to the grains and the grain boundaries. The Nyquist diagrams at low frequencies revealed the changes that took place in the grain boundary region, with the contribution of the grains being indicated by the formation of a second semicircle at high frequencies. The better sensing performance of the doctor bladed samples can be explained by their lower initial resistance values, bigger grain sizes and higher porosity.Fil: Savu, Raluca. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Ponce, Miguel Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Joanni, Ednan. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Bueno, Paulo Roberto. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Castro, Miriam Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Cilense, Mario. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Varela, Jose Arana. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Longo, Elson. Universidade Estadual Paulista Julio de Mesquita Filho; Brasi

EFFECT OF LANTHANUM ON MICROSTRUCTURE OF BaTiO3: PREPARED BY POLYMERIC PRECURSORS METHOD

Due to its high dielectric constant and low loss characteristics, barium titanate has been used in many applications, such as capacitors, piezoelectric devices, positive temperature coelficient thermistors, semiconductors and etc. Doping of BaTi03 ceramics very irnportant for obtaining very interesting characteristics for various apptications . In this paper it was investigated the effect of doping BaTio3 with La microstructure of BaTiO3 ceramics.. Powders of pure barium titanate and barium titanate doped with 0.3 mol %oLa. in the presence of small amount of manganese (0.01 mol% Mn), were prepared by polymeric precursors method through Pechini proccss (soft chemistry) which was carried out as a three stage process from organometallic complex. Synthesized powders were pressed into pallets using a cold isostatic press. Sintering was perfomed at 1300 C for 8h (Lenton furnace, UK). The heating rate was 10'C/min, liith nature cooling in air atmosfere [2] The X-ray results of samples sintered at 1300 C for 8h prepared fiom pure BaTiO3 powder arld doped BaTiO3 are given on Fig.1. and Fig.2., respectively. It. was approwed that. pure and doped BaTi03 were lornted as tetragonal crystal structurc

MICROSTRUCTURE DEVELOPMENT OF Bi4Ti3O12 AND BaBi4Ti4O15 CERAMICS PREPARED BY MECHANOCHEMICAL SYNTHESIS

Scveral bismuth-layered crystal structure and their properties have been investigated- in detail. However, a lot of aspects of the preparation and properties of barium bismuth titanate unexplored, whereas being promising candidate for memory applications. In present work barium-bismuth titanate (BaBi4Ti4O15-BBT) was prepared from stoichiometric, quantities of barium titanate and bisrnuth titanate obtained via mechanochemical synthesis. Barium titanate (BaTi3O12:-BT) has been synthesised from michture of BaO and Tio2 and bismuth titanate (Bi4Ti3O12-BIT) was prepared starting frorn Bi2O3 and TiO2 commercially available. Mechanochemical synthesis was performed in air atmosphere in , planetary ball mill, for BT during 60 min and for BIT during 360 min. Milling condition were: zirconium oxide jars and zirconium oxide balls, ball-to-powder weight ration 20:1 and determined basic disc and disc with jars rotation speed. The powder mixture of BT and BIT was homogenized for 30 min and after that sintered at 1100"C for 4h. Separatly, BIT was sintered at 1000 C for 12h, in both cases without pre-calcination step and by conventional sintering technique. The Fig. I. shows the phase formation and crystal structure of BIT, BT and mixture of this powders. Pattern of BBT powder sintered at 1100.c for 4h was analysed by XRD analysis revealing the existence of tetragonal phase (Fig. 2.). The morphology of obtained powders was examined by SEM and TEM method (Fig. 3. and Fig. 4.). It can be conclude that pattern of BIT consists of nanoparticles which size is less than 20 nm. Mixture of BIT and BT consists of agglomerates of varying size and morphology which size is about 250 nm. The microstructure development of BIT and BBT ceramics was followed by SEM. From Fig 5. and Fig. 6. it can be observed that BIT consists of plate-like grains but in the case of BBT beside plate-like grains exist and spheric grains, also' It is evident addition leads to the change in the microstructure development

Pyrosol preparation and structural characterization of SnO2 thin films

Polycrystalline tin oxide thin films were prepared from ethanol solution Of SnCl2.H2O (concentrations: 0.05, 0.1, 0.2 and 0.4 mol/dm(3)) at different substrate temperatures ranging from 300 to 450 degreesC. The kinetic deposition processes were studied in terms of various process parameters. The crystal phases, crystalline structure, grain size and surface morphology are revealed in accordance to X-ray diffractometry and scanning electron microscopy (SEM). Texture coefficients (TCs) for (110), (2 0 0), (2 11) and (3 0 1) reflections of the tetragonal SnO2 were calculated. Structural characteristics of deposited films with respect to varying precursor chemistry and substrate temperature are presented and discussed

Stability, characterization and functionality of proton conducting NiO-BaCe0.85-xNbxY0.15O3-delta cermet anodes for IT-SOFC application

There are many of properties of anodes based on proton conductors, like microstructure, conductivity and chemical stability, which should be optimized. In this work we were dealing with the influence of niobium on the chemical stability, microstructural and electrical characteristics of proton conducting NiO-BaCe0.85-xNbxY0.15O3-delta (NiO-BCNYx) anodes. Four anode substrates NiO-BCNYx of different Nb concentration were prepared using the method of evaporation and decomposition of solutions and suspensions (EDSS). Sintered anode substrates were reduced and their microstructural and electrical properties were examined before and after reduction as a function of the amount of niobium. Chemical stability tests showed strong influence of Nb amount on the chemical stability of anodes in the CO2. Microstructural properties of the anode pellets before and after testing in CO2 were investigated using X-ray diffraction analysis. Electrical properties of anode samples were examined by impedance spectroscopy measurements and the conductivity values of reduced anodes were more than 50 S cm (1) at 600 degrees C confirming percolation through Ni particles. Fuel cells were fabricated with aim to examine the functionality of anodes. During the fuel cell test the cell with Ni-BCNY10 anode achieved the highest performance, demonstrating a peak power density of 164 mW cm (2) at 650 degrees C, which confirmed the functionality of Ni-BCNY anodes. (C) 2014 Elsevier B. V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Influence of the indium concentration on microstructural and electrical properties of proton conducting NiO-BaCe0.9-xIn xY0.1O3-δ cermet anodes for IT-SOFC application

Optimization of the major properties of anodes based on proton conductors, such as microstructure, conductivity and chemical stability, is yet to be achieved. In this study we investigated the influence of indium on the chemical stability, microstructural and electrical characteristics of proton conducting NiO-BaCe0.9-xInxY0.1O 3-δ (NiO-BCIYx) anodes. Four compositions of cermet anode substrates NiO-BCIYx were prepared using the method of evaporation and decomposition of solutions and suspensions (EDSS). Sintered anode substrates were reduced and their microstructural and electrical properties were examined before and after reduction as a function of the amount of indium. Anode substrates tested on chemical stability in the CO2 atmosphere showed high stability compared to anode substrates based on commonly used doped barium cerates. Microstructural properties of the anode pellets before and after testing in CO2 were investigated using X-ray diffraction analysis. Impedance spectroscopy measurements were used for evaluation of electrical properties of the anode pellets and the conductivity values of reduced anodes of more than 14 S cm-1 at 600 °C confirmed percolations through Ni particles. Under fuel cell operating conditions, the cell with a Ni-BCIY20 anode achieved the highest performance, demonstrating a peak power density 223 mW/cm2 at 700 °C confirming the functionality of Ni-BCIY anodes.© 2013 Elsevier B.V. All rights reserved

Morphological study of the thorax of the five nymphal instars of Triatoma arthurneivai Lent & Martins (Hemiptera, Reduviidae, Triatominae)

Foi feito estudo morfológico da face dorsal, ventral e lateral do tórax de ninfas de 1º, 2º, 3º, 4º e 5º estádios de Triatoma arthurneivai por meio de microscopia eletrônica de varredura. Os cinco estádios ninfais podem ser reconhecidos pelos caracteres morfológicos observados no pronoto, mesonoto e metanoto. No 1º estádio nota-se ausência do colar, áreas glabras e tubérculos, que estão presentes no 2º estádio. No 3º estádio inicia-se a diferenciação das aletas alares. No 4º estádio ocorre expansão das quatro aletas alares, que, no entanto, não alcançam o abdome. No 5º estádio as aletas alares anteriores praticamente recobrem as posteriores. Na face ventral dos cinco estádios ninfais percebe-se duas (1+1) aberturas das glândulas metasternais. As áreas de evaporação das glândulas de Brindley localizam-se na mesopleura. Também foram observadas duas (1+1) áreas de evaporação na propleura dos cinco estádios ninfais.Scanning electron microscope (SEM) was done in order to study dorsal, ventral and lateral sides of 1st, 2nd, 3rd, 4th and 5th nymphal instars of Triatoma arthurneivai. The five nymphal instar can be recognized based on different pronotum, mesonotum and metanotum shapes and characteristics. In the 1st instar collar, hairless areas and tubercles are absent. The 2 nd instar presents collar, hairless areas and tubercles. In the 3rd instar occurs the development of wing pads. In the 4 th instar the four wing pads are expanded, but do not reach the abdomen and in the 5th instar the anterior wing pads almost overlap the posterior ones. At the ventral side, two metasternal glands openings (1+1) were found in all five nymphal instars. Brindley's gland evaporation areas (1+1) are located at the mesopleuron, as well as an evaporation area is located at the propleuron in all nymphal instars (1+1).Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

The effect of Cr concentration and preparation method on the microstructure and electrical characterization of SnO2-based ceramics

This paper reports a study of the influence of Cr concentration and preparation method in the electrical conductivity and microstructure of SnO2-based powders doped with Mn and Nb, prepared by an organic route (Pechini method) and a mixture of oxides. All the samples were compacted into discs and sintered at 1300 °C for 3h, resulting in ceramics with relative density varying between 81 and 99%. The powders were morphologically characterized by X-ray diffraction and their specific surface area was determined by N2 adsorption/desorption isotherms. Electrical conductivity characterization indicated that the conductivity decreases as Cr concentration increases, probably due to Cr segregation at grain boundaries, which reduces grain size, increasing the number of resistive boundaries, thus limiting the passage of current

Morfologia de ovos de Triatoma circummaculata e Triatoma rubrovaria (Hemiptera, Reduviidae)

OBJETIVO: Estudar morfologicamente ovos de T. circummaculata e T. rubrovaria. MÉTODOS: Quarenta ovos das duas espécies foram mensurados por meio de projetor de perfil Nikon modelo 6C, e utilizado o teste Student, para execução da análise estatística. As observações morfológicas foram feitas em microscópio eletrônico de varredura JEOL, modelo JSM-T330A. RESULTADOS/CONCLUSÕES: A análise estatística revelou que os ovos e as cascas de ovos de T. rubrovaria são significativamente maiores que os de T. circummaculata. Observações microscópicas mostraram que a borda corial, assim como a goteira espermática, são bem mais evidentes nos ovos de T. rubrovaria que nos de T. circummaculata. O exocório das duas espécies é formado por áreas poligonais, que são hexagonais em sua maioria. Foram observados também o momento da eclosão do embrião e os detalhes das exúvias embrionárias