Klaus-Michael Ochsenkühn

Comparison of the oxalate co-precipitation and the solid state reaction methods for the production of high temperature superconducting powders and coatings

Abstract High quality orientated YBa 2 Cu 3 O 7− x ( x =0.1–0.2) (YBCO) superconducting coatings were produced by the electrophoretic deposition technique. The fine particle YBCO powder used, was produced by the oxalate co-precipitation method on Au/Si and Pt/Si wafers. The optimized thermal treatment for both, powders and coatings, was followed by thermal analysis (thermogravimetry (TG) and differential scanning calorimetry (DSC)). The powders and coatings obtained, were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), optical microscopy, magnetic susceptibility and electrical resistivity measurements. It resulted that by the oxalate co-precipitation method finer and more homogeneous nanocrystalline YBCO powders were produced in comparison to the solid state reaction method, leading to more favorable conditions for their thermal treatment, like lower sintering temperature and shorter duration of the sintering process, as well as better superconducting properties, expressed by the shape and value of the corresponding magnetization curves. Furthermore, the production of the coatings was achieved in a shorter electrophoresis time by the powders from the co-precipitation method and the coatings produced were orientated having improved superconducting properties in comparison to those obtained by the solid state reaction method.

Effect of substrate materials on the superconducting properties of electrophoretically deposited YBa2Cu3O7−x coatings

Coatings of the high-temperature superconductor YBa2Cu3O7−x (x = 0.1–0.2) (YBCO), were deposited on commercial Ni,Ti and stainless steel substrates, by an electrophoretic deposition technique. Sintering and annealing procedures were followed in order to get strongly adherent superconducting films. The suitability of the used substrates was tested by measuring the stoichiometry and the superconducting properties of the deposited coatings by X-ray diffraction analysis (XRD), Raman spectroscopy and magnetization measurements with a superconducting quantum interference device (SQUID).

STUDY OF GREEK NEOLITHIC CERAMIC SHARDS FOR ELEMENT CONCENTRATION CHANGES IN RELATION TO THE AGE

At the reactor of the NCSR “Demokritos” epithermal irradiation was used in connection with the loss-free counting technique to investigate Neolithic ceramic shards from the Alepotrypa cave of Diros, Greece. The samples were subjected to a 10 min irradiation and a combination of two measurements, a first short one after a cooling time of 3 h, using loss-free counting and a second long one after 18 h in a well-type detector, allowing the study of 17 elements. Pottery of local origin can show depth-depending changes of composition caused by chemical influences from the geological environment, especially the groundwater, which may be or may have been in direct contact with the objects. It may occur also that, because of the progress of mining, various strata of a clay deposit differing slightly in chemical composition, transfer these changes to the ceramic. To study these possible effects determinations were performed with samples from three different depths and dated by the carbon-14 method, using carbonised objects of the same strata. Finally, changes in the concentrations of Mn, K, and Sb in relation to the age should be the effect of a reductive environment and of ion exchange processes, and could be assessed by statistical evaluation. This estimated age dependence of the concentrations should be taken into consideration when provenance studies are carried out.

Chemical Characterization and Comparison of Ceramic Samples from Ramnous and Laurion

Abstract Instrumental neutron activation analysis is, up to now, one of the most important analytical methods for the investigation of the chemical composition of ancient ceramics. At the reactor of the NCSR “Demokritos”, 21 ceramic fragments of the area of ancient Ramnous and 23 pieces from ancient Laurion were examined. The ceramic fragments were mainly from utilitarian vessels, which belonged to the fourth and third century BC. All pieces were without any decoration, aside from some black colours on one side. From all samples, data could be obtained for the elements As, Eu, La, Th, U, Sb, and Zn. The statistical evaluation of the mean values of these elements, as well as the correlation coefficients for the corresponding element combinations, showed that the fragments from ancient Ramnous were different from those of ancient Laurion. Cluster and factor analysis demonstrated that the samples from both places are separated into two independent groups. However, the separation is not very good, as the groups remain close together. The reason might be that the geological raw materials in such a closed area do not differ too much in its chemical composition profiles. Nevertheless, the results indicated that the utilitarian ceramics were obviously not objects for trade between these two regions, but remained items of local production.