Copper-deficiency in Ln2-xCexCuO4 (Ln=Nd, Gd) crystals and oxygen disorder in Gd2CuO4 crystals

The structure of seven Nd2-xCexCuO4 (x=0 and x=0.18) and Gd2CuO4 single crystals is determined by means of X-ray diffraction. All crystals have the Nd2CuO 4 tetragonal T' structure, space group I4/mmm (139). The copper site is found deficient (3 - 6%) in six crystals whereas both oxygen sites (within the CO2 planes O(1) and between rare earth layers 0(2)) remain fully occupied within standard deviation. The vibration ellipsoids of Nd, Cu and O(2) appear to be more ellongated in the c direction in Nd-based crystals reannealed in an inert atmosphere than in as-grown ones. The oxygen of the CuO2 basal plane (0(1)) in Gd2CuO4 is found off-centered in the a direction by 0.18 (2) Å.La structure de sept monocristaux de Nd2-xCexCuO 4 (x=0 et x=0.18) et Gd2CuO4 est déterminée par diffraction des rayons X. Tous les cristaux ont la structure tétragonale T' du Nd2CuO4 (groupe d'espace I4/mmm, n° 139). Un défaut de cuivre de l'ordre de 3 à 6% est trouvé dans six cristaux alors que les deux sites de l'oxygène (dans les plans CuO2 O(1) et entre les plans de terre rare O(2)) sont complètement occupés dans la limite d'erreur. Les ellipsoïdes de vibration des sites Nd, Cu et O(2) sont plus allongés parallèlement à l'axe c dans les cristaux recuit sous atmosphère inerte que dans les cristaux bruts de croissance. L'atome d'oxygène des plans CuO 2 (O(1)) dans Gd2CuO4 est trouvé décentré dans la direction de l'axe a de 0.18 (2) Å

The Ca0.80CuO1.93 phase : New way of synthesis by the sol-gel method

We report on the reaction kinetics for the Ca0.80CuO1.93 phase prepared by the sol-gel method using acrylamide for gelification. The phase was prepared 95% pure after a 2 hour treatment at 800°C. Comparative stability under vacuum and oxygen has been determined. The kinetics parameters for the decomposition have been established : the activation energy is Ea= 626 kJ/mol and the pseudo reaction order n = 0.5

Preparation and characterization of Au/ZrO2 composite obtained by oxidation of thin film ZrxAuy alloy

We present the preliminary results of a study aiming at preparing Au/ZrO2 mixed nanosized particles from thin films. In a first step, pure Zr and Au layers are alternatively deposited by RF sputtering on Si and W substrates under vacuum. Then, the intermetallic compounds are formed at high temperature under an inert atmosphere or in vacuum. The resulting samples are characterized by X-ray diffraction and by scanning electron microscopy. Keywords : Intermetallic compounds, Gold nanoparticles, Thin films, Gas sensor

Non-Stoichiometry and Complex Defects in the Structure of R-Ba-Cu-O Single Crystals Determined by Neutron Diffraction

AbstractThe crystal structure of several RBa2Cu3-yO6+z (R=Y,Ho) crystals are investigated by neutron diffraction using an exact solution for the twinned orthorhombic samples. For an oxygen concentration &gt;0.35 in the chains, the structure is orthorhombic due to an exclusive occupancy of the 0(4) site. A systematic and variable copper deficiency is observed on the Cu(l) site leading to a correlated defect on the chain oxygen O(4) and on the bridging oxygen O(l). Due to the presence of these defects, a transverse disorder is observed for the highest oxygen content with a residual occupancy of the forbidden O(5) site.</jats:p