含四銅氧層鉈系高溫超導體與其摻金屬衍生物的製備與特性鑑定之研究

Abstract

本研究之主旨係探討(一)傳統高溫固態燒結法(二)鹼性草酸/三乙基胺系 統共沉法合成具四銅氧層晶體結構的鉈系Tl2Ba2Ca3Cu4Oy(2234相)超導氧 化物之可行性與最佳製程，以製備高純度，組成均勻並具高臨界溫度之( Tc)2234超導體。前一個實驗在缺鉈多鈣的計量組成比下可合成Tc為 118K 之Tl1.7Ba2Ca3.3Cu4Oy超導體。而後者証實pH=10.4為各陽離子最佳共沉 條件，但鉈之計量須加以彌補後，具有潛力可製成含有雜質之2234超導相 。此外，藉由鉛離子之摻加，本研究除了確定鉛離子取代之飽和濃度 (10 atom %)外亦系統化地探討(Tl1-xPbx)1.7Ba2Ca3.3Cu4Oy系列中載子 濃度對2234相臨界溫度(Tc)與樣品磁化率與溫度關係之效應。本系列具 有 強列之釘扎效應，其成因十分值得深入探討。 The optimal conditions invovled in the synthesis of high-Tc Tl2 Ba2Ca3Cu4Oy(2234 phase) superconductor with crystal structure containing four copper-oxygen layers was investigated by (a) conventional high-temp. solid-state and (b) alkaline triethylammoniumoxalate coprecipitation methods, respectively, to prepare 2234 phases with high puritygood homogenity and high critical temperature(Tc).A series of superconductors with nominally thallium-deficiend and calcium- rich compositions were prepared by solid-state method, with highest Tc of 118K found in Tl1.7Ba2Ca3.3Cu4Oy phase. With the coprecipitation route, the optimal pH for the coprecipitation of common cations was determined to be 10.4. However, superconducting 2234 phase with impurities could be ynthesized only with appropriate compensation of Tl2O3 in the preparative reactions. On the other hand, we have also systematically investigated the effect oflead-doping in series of (Tl1-xPbx)1.7Ba2Ca3.3Cu4Oy on carrier concentration, temperature-dependent magnetizatic susceptibility, and Tc the 2234 phase.The saturated dopant concentration was determined to be 10 atom % and the strong pinning eggect observed in the series of lead-doped samples is worth of further investigations.