La2-xSrxCu1-yZnyO4 (x∼0.21)的加Zn效應：X光吸收光譜學測量

The Effect of Zn on La2-xSrxCu1-yZnyO4 (x~0.21)：X-ray absorption spectral measurement

雷棋雄(Qi-Xiong Lei)

指導教授 ： 張秋男

國立臺灣師範大學/理學院/物理學系/碩士(2001年)

摘要

本論文研究的目的在探討Zn的摻雜對La2-xSrxCuO4樣品的晶體結構以及電子結構的影響。 我們利用同步輻射測量各樣品的 O 1s及Cu LⅡ,Ⅲ 的吸收光譜研究它們在Fermi energy附近的電子結構變化。
La2-xSrxCu1-yZnyO4是摻雜Zn2+離子取代Cu2+離子。從X-ray粉末繞射結果可知La2-xSrxCu1-yZnyO4是四方晶格結構，隨著x的增加a軸有逐漸變小、c軸有逐漸增加的趨勢，而Zn的摻雜對a、c軸的影響在誤差範圍內無法看出具體的效應。當材料未摻雜Zn時(y=0)，在超摻雜(overdopping)區域是隨著Sr取代量的增加，超導臨界溫度是逐漸下降的，從吸收光譜可發現Ia(528.4 eV；表示電洞濃度的貢獻)有逐漸增強的趨勢，顯示出隨著Sr2+摻雜費米面附近的電洞態有增加的趨勢。另外當樣品加入1%的Zn取代銅時，從SQUID測得的Tc有明顯的抑制下降效應，而從吸收光譜的量測結果顯示，在實驗誤差範圍內Zn的摻雜並沒造成價電帶強度的改變，顯示出Zn對超導的抑制來源並非來自於電子結構的改變。

關鍵字

超導體 ； 吸收光譜

並列摘要

The purpose of this study is to investigate the effects of Zn on the lattice and electronic structures of La2-xSrxCuO4.
Series of samples of La2-xSrxCu1-yZnyO4 (0.17≦x≦0.30, y=0.01) are prepared by chemical solid reaction. The results of X-ray diffraction(XRD) show that all samples are tetragonal. Lattice constant a is found to decrease with the increase of x while the change of c is in the opposite. No effect of Zn on a and c found within the experimental accuracy.
Synchrontron radiation is used to obtain the absorption spectra of O1s and Cu LⅡ,Ⅲ for each sample. It is found in O1s pre-edge peak that Ia (528.4 eV, transition to the hole state in the valence band) is gradually enhanced. It shows that the hole states near the Fermi level in the valence band increases with the concentration of Sr2+.
When Cu2+ is substituted by 1% Zn2+ , the Tc , as derived from the magnetization curve by using a SQUID(Superconducting Quantum Interference Device) decrease. However, from one to one comparision between the samples with and without Zn doping, no esssential change of the O1s pre-edge peak is observed within the statistical errors. We conclude that the substitution of Zn for Cu does not affect the electronic structure of the sample and thus the drop of Tc does not result from the electronic structure.