稀土元素取代釔鋇銅247超導體高壓法合成與特性鑑定之研究

Abstract

本實驗是利用高壓固態合成法研究稀土元素取代釔鋇銅247相中釔 結構及 物性之影響。當以鐠元素取代釔247相時，Tc會隨著取代量增加而呈線性 的降低，當取代濃度達80%時已無超導性。此外晶格常數亦隨取代量增加 而呈線性增加。磁性量測也提供鐠取代對超導性影響。類似特性改變也發 現在鐠一系列取代鉺-247及鏑-247系統。此外本研究也合成其它含稀土元 素之247相，從這些稀土元素所形成的247相中可以發現其超導臨界溫度具 有隨離子減小而升高的趨勢。此外為了探討鐠無法形成純鐠-247相，也利 用化學分析電子儀對鐠做價數分析，用掃描式電子顯微鏡來觀察表面微結 構。 This research is attempted to study the effect of rare- ubstitution for yttrium on the crystal structure and physical properties in the Y-247 phase system by high-pressure solid- state synthesis. The superconducting transition temper-(Tc) determined by both resistive and magnetization mothod was found to decrease monotonically with increasing Prnt in the Pr- substituted Y-247 phases. The substitutionetermined to be 70-80% and no superconductivity was found when X=0.80. In addition, the lattice constants were found to increase linearly with increasing Pr atom, photo-spectra were measured on the samples of the Pr- substituted 247 phases with X=0,0.1.0.4 and 0.7,and a 3+ state is likely to be present in the samples. Similar results were also found in the Pr substitution of the rare-earth containing7(R=Er and Dy)phases though the individual substitutionifferent. On the other hand, we have also synthesized a series of=Gd,Nd and Eu) and investigated the effect of size ofthe superconductivity of the R-247 phases. Tc was found to decrease linearly with increasing size of R cations. Attempts to prepare both Pr-124 and Pr-247 phases failed due to the formation of the PrBaO 113 phase and future attempts will require more efforts in controlling the valence state of Pr cation. A series of scanning electron microscopic studies were also carried out on a series of Pr-substituted 247 sample to investigate the microstructure of the samples prepared under high temperature and high pressure conditions.