Energy Dispersive X-ray Spectroscopy (EDS) was used to show that the elemental homogeneity of YBa2Cu3O7 powders can be improved substantially by heating the powder in a nitrogen dioxide-containing atmosphere (e.g., 950°C), followed by annealing in oxygen at 950°C, and slow-cooling to room temperature. The improved homogeneity results in a substantially larger flux exclusion signal for the NO2-treated powder, as measured by both ac and dc techniques. The experimental results suggest a mechanism which involves the formation of a small amount of molten Ba(NO3)2, which acts as a flux that dissolves the constituents and reprecipitates them as high purity YBa2Cu3O7.

The production of high performance YBa2Cu3O7 using nitrogen dioxide

On peut ameliorer substantiellement l'homogeneite elementaire de poudres de YBa 2 Cu 3 O 7 en les chauffant a 950°C dans une atmosphere contenant NO 2 , puis en procedant a un recuit dans O 2 au-dessus de 750°C et en refroidissant lentement jusqu'a temperature ambiante. L'amelioration de l'homogeneite entraine une augmentation du signal d'exclusion de flux pour la poudre traitee par NO 2 , comme le montrent les mesures realisees en courant alternatif.

The Use of Nitrogen Dioxide to Improve the Superconducting Properties of YBa2Cu3O7

Ceramic materials have been known for several thousands of years, but an intensive research in the last two decades was leading to the advanced materials which are becoming established in todays technology and which are expected to form the backbone of developments to the next century. The properties of the final ceramics are greatly predeterminated by the characteristics of the starting powder materials. This situation stimulated the increase of studies on preparation of taylor made powders with regard to purity, homogeneity, reactivity, grain size and grain size distribution. Starting with the classical solid state reaction a detailed review is given of wet chemical preparation techniques for perovskite type materials. Briefly some physical methods of powder preparation are mentioned. Furthermore important processes accompanying the preparation as drying, control of agglomeration behaviour and powder characterization are discussed, respectively.

Methoden zur Pulverpräparation für technische Keramiken

High Tc superconductor, Ba2Y1Cu3O7-x thick film including Ag metal has been developed by the sintering of Ba2Y1Cu3O7-x single phase powder and Ag2O powder In general, Ag2O varies to metal Ag around 400°C, which does not react with Ba2Y1Cu3O7-x and metal Ag melts around 800°C The resistivity in the normal conductance region depends greatly on the content of metal Ag in this composite thick film and decreases with increasing the content of metal Ag Superconducting temperature was 85–90 K Current density of 132 A/cm2 was the most highest measured value in this study

Kouichi Niihara

Papers

Preparation of High Tc Superconductor Oxide Ceramics by Partial Oxalate Method and Their Evaluations