Effects of carbon incorporation on doping state of YBa2Cu3Oy

Effects of carbon incorporation on the doping state of YBa2Cu3Oy (Y-123) were investigated. Quantitative carbon analysis revealed that carbon could be introduced into Y-123 from both the precursor and the sintering gas. Nearly carbon-free (< 200 ppm) samples were prepared from a vacuum-treated precursor by sintered at 900 &#730;C and cooling with 20 &#730;C /min in flowing oxygen gas. The lower Tc (= 88 K) and higher oxygen content (y = 6.98) strongly suggested the overdoping state, which was supported by the temperature dependence of resisitivity and thermoelectric power. The nuclear quadrapole resonance spectra and the Raman scattering spectra indicated that there was almost no oxygen defect in the Cu-O chain in these samples. On the other hand, in the same cooling condition, the samples sintered in air stayed at optimal doping level with Tc = 93 K, and the intentionally carbon-doped sample was in the underdoping state. It is revealed that about 60% of incorporated carbon was substituted for Cu at the chain site in the form of CO32+, and the rest remains at the grain boundary as carbonate impurities. Such incorporation affected the oxygen absorption process in Y-123. It turned out that the oxygen content in Y-123 cannot be controlled only by the annealing temperature and the oxygen partial pressure but also by the incorporated carbon concentration.Comment: 16pages, 9figure

Brevetto o pubblicazione scientifica? Strategie per risolvere il dilemma

L'evento è l'ultimo appuntamento del ciclo di seminari "Strumenti per conoscere la letteratura brevettuale", organizzato da Sardegna Ricerche e dall'Industrial Liaison office dell'Università di Cagliari, in collaborazione con l'Associazione italiana documentalisti brevettuali, all'interno del progetto IPS - Intellectual Property center Sardegna.Il seminario ha approfondito il tema dei brevetti generati in ambito accademico, dal punto di vista: della struttura (perché una organizzazione pubblica di ricerca dovrebbe tutelare le invenzioni che scaturiscono dalla sua attività); delle persone (benefici e malefici dei brevetti rispetto ai ricercatori/tecnologi che li generano); tecnico (brevetti "industriali"/brevetti "accademici", come si individua un'invenzione da tutelare, a che livello di sviluppo conviene brevettare, come si costruisce, si gestisce e si valorizza un portafoglio di tecnologie "accademico", brevettare o pubblicare?).2014-06-04Facoltà di Scienze economiche, giuridiche e politiche dell'Università di Cagliari - Aula Magna "Maria Lai"Strumenti per conoscere la letteratura brevettual

FLUX-FLOW DISSIPATION IN GDBA2CU3O7 AT MICROWAVE-FREQUENCIES

We report measurements of the magnetic-field-dependent microwave dissipation in high-purity GdBa2Cu3O7-delta pellets with different grain sizes, by means of a cavity technique with no field modulation. The dissipation is due to the intragranular viscous vortex motion at fields greater than or similar to 0.02 T, and to weak-links at low fields (H 0.02 T) has to be ascribed to the free motion of flux lines

Chemical insights obtained by modelling the structure of high-temperature superconductors using AX<SUB>3</SUB> close-packing and transferable single atom paramters

This article does not have an abstract

Electron spin resonance evidence for the role of copper ions in interlayer coupling in layered copper oxycarbonates

Electron spin resonance (ESR) studies have been carried out on the layered copper oxycarbonates (alternating layers of CuO2 and CO2-3) with the nominal composition Ba3SrCu2O6.2CO2 and their reaction products with ammonium slats. The ESR signals typical of copper ions in square-planar geometry with a slight orthorhombic distortion presumably arise from the copper ions being incorporated in the carbonate layer. A simple grinding procedure at room temperature using (NH+4)nXn- (X=F-, (NO3)-, (VO3)-, (HPO4)2-) incorporates Xn- anions in the structure with the liberation of ammonia. The environment of the cop per ion in the carbonate layer is thus changed without altering the structure. The g3 values are most affected by this reaction showing that the filled eg orbitals are oriented in the plane of the carbonate layer. The half-filled eg orbitals (transforming s dx2-y2 orbitals) are oriented out of the plane. This suggests that the copper ions in the carbonate layers are probably involved in introducing magnetic coupling between the CuO2 layers