We have studied the influence of amorphous and crystalline substrate materials, such as a-Si and a-Si:H, as well as c-Si(111), (100), and hydrogen implanted c-Si(111) on the outdiffusion of Si through an evaporated Au thin film, and its subsequent oxidation in atmosphere. Using Auger electron spectroscopy depth profiling we observed that the SiO2 layer thickness d formed on top of the Au film strongly depends on the type of substrate material giving most enhanced Si outdiffusion from amorphous ones. The metastable phase AuxSi is detected on both interfaces between the Au/Si and the SiO2/Au layers. A temperature independent ratio, dH/d ≊ 2, is observed for the oxide layer thickness of substrates with and without hydrogen. This is a surprising result, which indicates the influence of nonthermodynamic effects, probably related to the surface structure of the semiconductor substrates and a strong influence of hydrogen. A model of the layer structure is developed, which permits the calculation of diffusion activation energies resulting in qHD ≂ qD ≂ 1.0 (eV) for the diffusing species on substrates with and without hydrogen, respectively.

Large amounts of solid wastes are discarded in the ornamental rocks industry. This work investigates the incorporation of ornamental rock-cutting waste as a raw material into an aluminous porcelain body, replacing natural feldspar material by up to 35 wt.%. Formulations containing rock-cutting waste were pressed and sintered at 1350 °C. The porcelain pieces were tested to determine their properties (linear shrinkage, water absorption, apparent density, mechanical strength, and electrical resistivity). Development of the microstructure was followed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The results showed that ornamental rock-cutting waste could be used in aluminous porcelains, in the range up to 10 wt.%, as a partial replacement for traditional flux material, resulting in a valid route for management of this abundant waste.

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Doped lanthanum chromite-based ceramics are the most widely used interconnector material in solid fuel cells (SOFC) since they exhibit significant electrical and thermal conductivity, substantial corrosion resistance and adequate mechanical strength at ambient and high temperatures. The disadvantage of this material is its high cost and poor ductility. The aim of this study is to determine the mechanical and oxidation behavior of a stainless steel (AISI 444) with a LaCrO 3 deposition on its surface obtained through spray pyrolisis. Coated and pure AISI 444 materials were characterized by mechanical properties, oxidation behavior, X-ray diffraction and scanning electronic microscopy. Results indicated that the coated material displays better oxidation behavior in comparison to pure stainless steel, but no improvement in mechanical strength. Both materials indicate that deformation behavior depends on testing temperatures.

The effect of copper doping on structural, electrical, and optical properties of zinc oxide films was evaluated. Copper-doped films (ZnO:Cu) were successfully deposited on a glass substrate by spray pyrolysis at doping levels of 0, 2.5, and 7.5 at% (ZnO, ZC2.5, ZC7.5). All films were polycrystalline, single-phase with ZnO hexagonal wurtzite structure. The films presented nanostructured crystallites, from 36.7 to 38.2 nm. Cu doping increased the electrical conductivity of the ZnO films; this change was proportional to the Cu concentration. The films presented high optical transmittance of 70-80% in the visible wavelength. The energy gap decreased upon Cu doping. The photoluminescence spectrum of all films displayed an intense ultraviolet emission and a weaker blue emission. The emissions shifted to lower wavelengths with increasing dopant concentrations. ZC7.5 presented the most promising properties for an application as transparent conducting oxide: intense optical transmittance and UV photoluminescence, also the lowest electrical resistivity.

INTRODUÇÃOAs células a combustível de óxido sólido (SOFCs) são estruturas multicamadas de materiais cerâmicos, que utilizam a combinação química entre oxigênio e um combustível para gerar energia elétrica. Trata-se de uma tecnologia eficiente e de concepção ambiental, com emissões desprezíveis quando comparada a outros processos de combustão [1-5]. ResumoForam produzidos filmes de zircônia estabilizada com 8 mol% de itria (8YSZ) por spray pirólise, que podem ser aplicados como eletrólitos de células a combustível de óxido sólido. A técnica de spray pirólise tem como vantagens ser de simples manuseio, baixo custo de operação, versátil e eficiente na obtenção dos filmes cerâmicos. Entretanto, como desvantagens principais encontram-se a grande quantidade de fatores que interferem na qualidade e a reprodutibilidade. Visando estabelecer a influência destes parâmetros na morfologia dos filmes, utilizou-se a técnica de planejamento de experimentos, com três parâmetros determinados com principais: temperatura de deposição (T), fluxo da solução (F) e tempo de deposição (t). A morfologia dos filmes foi analisada por microscopia ótica com aumentos de 400x em campo claro e escuro, avaliando a presença de trincas, poros, partículas salinas e rugosidade. Para a execução das análises empregou-se o software ImageJ, que possibilitou a quantificação da influência dos parâmetros de deposição na morfologia. Realizou-se a modelagem dos resultados obtendo-se que os filmes de melhor morfologia, dentro dos parâmetros estudados, seriam produzidos com temperatura de deposição 320 °C, tempo de deposição 32 min e fluxo 1,4 mL/min. O filme de 8YSZ depositado com os parâmetros modelados foi tratado termicamente a 1000 ºC por 300 min com o objetivo de se alcançar a estrutura cristalina cúbica do tipo fluorita. A estrutura do filme foi analisada por difração de raios X, apresentando-se policristalino e com estrutura cúbica de face centrada do tipo fluorita, com orientação preferencial dos grãos no plano (111). As propriedades morfológicas dos filmes foram analisadas por microscopia de força atômica, indicando ter-se obtido um filme homogêneo, isento de microtrincas e microporos. Palavras-chave:spray pirólise, SOFC, YSZ. Abstract Films of 8 mol% yttria-stabilized zirconia (8YSZ) were prepared by spray pyrolysis, which can be used as electrolytes in solid oxide fuel cells. The spray pyrolysis technique has advantages such as simple handling, low cost of operation, versatile and effective in getting ceramic films. However, the major disadvantages are several parameters that can affect quality and reproducibility of the deposited films. Therefore, in order to establish the influence of the deposition parameters on the morphology of the films, the technique of factorial design of experiments was used with the determination of three parameters: deposition temperature (T), solution flow (F) and deposition time (t).

In this work, copper-doped zinc oxide films (ZnO:Cu) were deposited by spray pyrolysis on glass substrates. The influence of doping concentration (0-10 at.%) on morphological, structural, optical and electrical properties of the ZnO:Cu films was investigated. Electrical characterization consisted in measuring the variation of electrical conductivity with temperature; they presented a typical semiconductor material behavior. Based on x-ray diffraction (XRD) analysis, it was able to confirm that the films are polycrystalline having a wurtzite hexagonal structure, preferentially oriented in the c-axis (002), and the crystallite size ranged from 41.60 to 50.70 nm. The optical characterization revealed that ZnO:Cu films present band gap energy between 3.18 and 3.27 eV. The films were homogeneous with good adhesion to the substrate. The results indicate the viability of using them in optoelectronic devices.

Films of lanthanum strontium manganite, LSM (La 0.8 Sr 0.2 MnO 3 ) were deposited on yttria stabilized zirconia (YSZ) substrates by different methods aiming to establish the most suitable route to prepare cathodes for solid oxide fuel cells (SOFC). Samples were obtained by using a solution of lanthanum, strontium and manganese nitrates or a dispersion of the LSM powder in this solution. Both commercial and synthetized LSM powders were used, the last one obtained by amorphous citrate method. The films were deposited by spray pyrolysis on YSZ substrates prepared by uniaxial and isostatic pressing. Samples were characterized by scanning electron microscopy, confocal laser scanning microscopy, X-ray diffraction and two-probe conductivity measurements. The area specific resistance and relaxation to cathodic activation were measured by electrochemical impedance spectroscopy. The substrate obtained by uniaxial pressing and the commercial LSM produced films with the highest amount of surface cracks. The film obtained from the suspension showed area specific resistance and activation energy lower than the other produced from the solution. For both samples, the cathodic activation process resulted in an initial reduction of the total resistance of around 20%, the sample produced from the suspension being more resistant to relaxation. Therefore, the LSM suspension is more suitable than the salts solution for preparing films by spray pyrolysis on YSZ substrates to obtain efficient cathodes for SOFC.