Wyniki 1-5 spośród 5 dla zapytania: authorDesc:"Jean Raymond Gavarri"

Characterization of lanthanum lutetium oxide thin films grown by pulsed laser deposition

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Exposure to ionizing can occur in the range of industries, medical institution, educational and research establishments and nuclear fuel cycling facilities. Adequate radiation protection is essential for the safe and acceptable use of radiation, radioactive materials and nuclear energy [1]. Due to large number of different applications, there are many alternatives of materials and design for radiation sensors or detectors. To optimize the trade-offs that exist among the requirements, different materials, geometric arrangements and different physical detection techniques are used [2]. A number of efforts were devoted to investigate the influence of radiation on the properties of metal-oxide materials [3÷5]. Metal oxides are interesting for their low-cost and simplicity. Properties of metal oxides materials are directly or indirectly connected to the presence of defects. In particular oxygen vacancies determine the optical, electronic and transport properties of the materials and usually dominate the chemistry of its surface. The promising materials for gamma sensor applications are TiO2, TeO2, NiO, CeO2, In2O3, LaFeO3, LaLuO3 [2, 3, 6, 7]. The gamma detecting oxide materials can be in the form of both: thin or thick films [3]. Only crystallized LaLuO3 exhibits luminescence properties that could be used in detection. There are a wide variety of techniques for deposition of thin films. The examples are thermal evaporation (also known as vacuum vapour deposition), electron-beam evaporation, magnetron sputtering, chemical vapour deposition (CVD) and molecular beam epitaxy (MBE) [8÷10]. Pulsed laser deposition was already used to grow amorphous LaLuO3, mainly as high-K gate dielectrics [11], but barely crystallized LaLuO3 films were grown by this technique. For this reason, in the present work to obtain crystallized LaLuO3 thin films PLD technique was used and the morphology and chemical composition of thin films were investigated. I[...]

Lanthanum hydroxycarbonates and langasite ceramics: stability, infrared spectroscopy and electrical behaviors.

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Optimized synthesis routes allowed preparing polycrystalline hydroxycarbonate La2O3-x(OH)y(CO3)z and langasite La3Ga5SiO14. Langasite precursor was used to form a first langasite polycrystalline thin film. The thermal stability of lanthanum hydroxycarbonates La2O3-x(OH)y(CO3)z (noted LHC) resulting from surface hydration and carbonation of La2O3 was studied by Fourier Transform infrared spec[...]

Catalytic behaviours and electrical conduction changes in BaCeO3 ceramics synthesized by sol-gel method

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BaCeO3 (BCO) ceramics and related perovskite type compounds were intensively studied because of their high temperature potential applications (e.g. for fuel cell and electrocatalysis technologies) [1÷3]. They were regarded as very promising candidates as solid electrolytes in electrochemical devices such as solid oxide fuel cells (SOFCs) and gas sensors [4÷6]. These perovskite type structures were highly interesting mainly because of their high ionic conductivity. More recently, we found that BaCeO3 exhibited heterogeneous photocatalytic activities for water splitting [7÷10]. Doped barium cerate materials were also investigated as proton conductors in humidified reducing atmosphere at intermediate temperature: these perovskite type materials were also considered as promising electrolytes for SOFCs [11÷14]. The microstructure and the presence of carbon dioxide in the ambient atmosphere were also considered as potential parameters that could condition the conductivity mechanisms [15]. These oxide materials were also found to present high interest as catalysts for oxidation reaction because of their high capacity of oxygen conduction. Recently solid gas interaction analyses between BCO and methane CH4 in air-CH4 flows were published [16, 17]. However, in our knowledge, the solid gas interactions between BaCeO3 and carbon monoxide CO were never studied. In this work, we first study the conversion of CO in air-CO gas mixtures interacting with barium cerate powder, and then we determine the high temperature electrical conductivity of compacted pellets of barium cerate. We report a new synthesis method allowing preparing BaCeO3 perovskite ceramics at moderate temperature (1100°C). Characterizations are achieved using X-ray diffraction and transmission electron microscopy. The catalytic properties are investigated from analyses of emitted gases from Fourier Transform infrared spectroscopy (FTIR). The electrical properties are studied [...]

Electrical studies of phase stabilities in the Ce2O(CO3)2·H2O/CeO2 and LaOHCO3/La2O3 systems

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To develop new selective sensing devices for gas detection, working in environmental conditions, we are investigating materials susceptible to interact successively with H2O (vapor), CO2 gas and finally with a specific gas such as methane CH4, carbon monoxide CO. One possible solution for improving the selectivity should be to use oxide phases highly sensitive to carbonatation or hydration, presenting successive phases stable at increasing temperatures [1÷6]. Two systems are presently investigated to determine their relative reactivities with CO2 and H2O: the La2O3-H2O-CO2 and CeO2-H2OCO 2 rare earth based systems. The lanthanum based system presents a series of phases LaOHCO3, La2O2CO3 and La2O3 stable in three different temperature ranges [7÷15]. It also presents a high interest because of the strong capacity of hydration of the oxide phase La2O3. In addition, we have recently shown that these La2O3, LaOHCO3 and La2O2CO3 phases might present interesting catalytic activities, in presence of methane-air (CH4-air) and carbon monoxide-air (COair) flows at various temperatures [16]. The cerium system seems to behave differently with one stable Ce2O(CO3)2·H2O phase (with 3+ valence for cerium ion) and the CeO2 oxide (ceria) stable under air with 4+ valence for cerium ion [17, 18]. In the present study, we focus our attention on the decarbonatation kinetics of the carbonate phases and on the carbonatation kinetics of the oxide phases: the main objective of these analyses should be to determine their electrical sensitivities during gas solid interactions with CO2. These correlations between phase changes and electrical responses are not known, and they could deliver interesting informations to develop miniaturized electrical devices including microsensor or microabsorber systems. Exp erim ental detail s Elaboration The initial samples were first synthesized following the same approach. A first step consisted in preparing two c[...]

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