Electric transport measurements on bulk, polycrystalline MgB2 samples prepared at various reaction temperatures

摘要

Aseriesofdisk-shaped,bulkMgB2superconductors(samplediameterupto4cm)waspreparedinordertoimprovetheperformanceforsuperconductingsuper-magnets.SeveralsampleswerefabricatedusingasolidstatereactioninpureAratmospherefrom750to950oCinordertodeterminetheoptimumprocessingparameterstoobtainthehighestcriticalcurrentdensityaswellaslargetrappedfieldvalues.Additionalsampleswerepreparedwithaddedsilver(upto10wt.-%)totheMgandBpowder.Magneto-resistancedataandI/V-characteristicswererecordedusinganOxfordInstrumentsTeslatronsystem.FromArrheniusplots,wedeterminetheTAFFpinningpotential,U0.TheI/V-characteristicsyielddetailedinformationonthecurrentflowthroughthepolycrystallinesamples.Thecurrentflowisinfluencedbythepresenceofporesinthesamples.Ouranalysisoftheachievedcriticalcurrentstogetherwithathoroughmicrostructureinvestigationrevealsthatthesamplespreparedattemperaturesbetween775°Cand805°Cexhibitthesmallestgrainsandthebestconnectivitybetweenthem,whilethesamplesfabricatedathigherreactiontemperaturesshowareducedconnectivityandlowerpinningpotential.Dopingthesampleswithsilverleadstoaconsiderableincreaseofthepinningpotentialandhence,thecriticalcurrentdensities...