Abstract
我們以Sr離子取代Ba的位置;以Fe及Mo取代Cu的位置,共製備Y(Ba1-xSrx)2 (Cu1-0.07xMo.07x)3O7-z及YSr2Cu3-xFexO7-z等系列樣品,並以含氧量滴定,結構精算,梅思堡光譜等,對樣品的特性加以分析.同時,我們亦以鍵價的計算對電洞的轉移與結構特性的關聯加以研究.最後我們以鍵價與tolerance factor的變化對123相的結構穩定性加以討論,所得之重要結果如下: (1)以Sr取代Ba離子的效應為晶格收縮及Ba離子往Cu-O平面移動,造成O(2)與O(3)上電洞的轉移與Tc的下降. (2)從Fe取代的研究比較,YSr2Cu3O7-z與YBa2Cu3O7-z的系統幾乎一致,我們認為Sr與Ba離子的主要作用在提供一穩定的結構,使Cu-O平面與 Cu-O鏈維持特定作用,對超導的特性沒有直接的影響. (3)在YBa2Cu3O7-z的系統中,高價數Mo離子的取代效應受其取代位置的影響:當Mo離子取代Cu(2)時,是一電洞充填的機制,經電子攙雜使 Cu-O平面上的電洞被中和.除此之外,可能也有古柏對的破壞等效應,使其對超導性的破壞與大於取代在Cu(1)的位置. (4)在YSr2Cu3O7-z系統中,Fe離子取代Cu(1)時,是藉由O(1)離子的位移將電洞從Cu-O平面轉移至Cu-O鏈,使超導臨界溫度下降此為電荷轉移機制 (charge transfermechanism). (5)經由結構精算,鍵價理論及tolerancefactor的分析,我們認為 YSr2Cu3O7-z不穩定的原因是:Sr離子的離子半徑太小,造成Sr與O(1)的距離變大,使得Sr離子的鍵價和下降及晶格應力變大,使結構不穩定.(6)根據tolerance factor的計算,我們認為穩定YSr2Cu3o7-z的主要方法是增加Sr離子的有效離子半徑或Sr離子的鍵價和.We have synthized two series compounds of Y(Ba1-xSrx)2(Cu1-0.07x Mo0.07x)3O7-z (0<x<1.0) and YSr2Cu3-yFeyO7-z (0.3<y<3.0). Wecharacterized the compounds with iodometry, structure analysis,and bond valence sum calcuation and the detail results arelisted below: (1) As Ba ion was substituted by Sr will suppressthe Tc which was deduced from the lattice contraction and thedisplacement of Ba ions. (2) The properties of the YSr2Cu3O7-zsystem are similar to the YBa2Cu3O7-z system and the role ofcharacter of Sr and Ba ions is the stabilization of crystalstructure. (3) As the Mo ion substituted into the Cu(2) sitewill induce hole filling and suppress the Tc seriously. (4) Asthe Fe ion substituted into the Cu(1) site will induce chargetransfer and suppress the Tc. (5) The instability of YSr2Cu3O7-z could be deduced from the low bond valence sum of Sr ion andthe lattice stress. (6) The methods to stabilized the structureof YSr2Cu3O7-z are increasing the effective ionic radius andbond valence sum of Sr ion.