摻雜對於 LiCu2-xZnxO2 與 HoxMn1-xS 材料拉曼散射光譜之影響

Effects of substitutional doping on Raman-scattering spectra in LiCu2-xZnxO2 and HoxMn1-xS materials

蔡欣樺(Hsin-Hua Tsai)

指導教授 ： 劉祥麟

國立臺灣師範大學/理學院/物理學系/碩士(2012年)

摘要

我們研究掺雜 Zn 離子之 LiCu2O2 單晶與掺雜 Ho 離子之MnS 多晶的拉曼散射光譜響應。藉由分析掺雜離子對拉曼特徵峰的影響，探討晶格結構與磁性和電性相轉變之間的相關性。
首先，LiCu2O2 於室溫展現 7 個 Ag 對稱性與 3 個 B1g 對稱性拉曼活性振動模，其頻率位置約為 106 cm-1、119 cm-1、173 cm-1、297 cm-1、362 cm-1、465 cm-1 及 557 cm-1，與 161 cm-1、494 cm-1 及 569 cm-1。隨著摻雜 Zn 離子濃度的增加 (x = 0.03 與 0.07)，LiCu2O2 拉曼散射光譜顯現值得注意的變化包括：(i) 與氧原子沿 ab 平面振動有關之 161 cm-1 拉曼峰展現紅移，符合 x 光繞射實驗結果之 ab 軸晶格常數增大；(ii) 我們認為 106 cm-1 特徵峰屬於拉曼活性振動模，此與文獻[Phys. Rev. B 69, 104421 (2004).]所認定之 two-magnon continuum 不符；(iii) 摻雜 7 % Zn 離子的 LiCu2O2 在磁性相轉溫度 14 K 以下，492 cm-1 拉曼峰展現微小紅移，推測其與自旋-聲子耦合有關。
其次，Ho0.01Mn0.99S 於室溫展現 4 個拉曼活性振動模，其頻率位置約為 135 cm-1、227 cm-1、333 cm-1 及 585 cm-1。隨著摻雜 Ho 離子濃度的增加 (x = 0.10 與 0.30)，由於 Ho3+ 離子半徑大於 Mn2+，333 cm-1 與 585 cm-1 拉曼峰有逐漸紅移的現象；(ii) 低溫時，Ho0.01Mn0.99S 展現低頻擴散拉曼散射響應，推測其與載子碰撞傳導電性有關；(iii) 333 cm-1 與 585 cm-1 拉曼峰的權重分別在高溫 350 K、500 K 及 620 K 附近顯示快速下降的趨勢，與電阻率和晶格常數的變化相互呼應，我們推測其與電子雲軌道有序性、或電荷有序性有關。

關鍵字

鋰銅氧 ； 鈥錳硫 ； 拉曼散射光譜 ； 軌道有序性 ； 擴散式響應

並列摘要

We present the Raman-scattering studies of Zn doped LiCu2O2 single crystals and Ho doped MnS polycrystalline samples. Our aim is to investigate the effects of doping on the lattice excitations in these novel materials.
First, room-temperature Raman-scattering spectrum of LiCu2O2 shows ten phonon modes at about 106 cm-1, 119 cm-1, 173 cm-1, 297 cm-1, 362 cm-1, 465 cm-1, and 557 cm-1 as well as 161 cm-1, 494 cm-1 , and 569 cm-1, displaying symmetries of Ag and B1g, respectively. As the concentration of the Zn ion increases (x = 0.03 and 0.07), there are three important features to these spectra: (i) the 161 cm-1 phonon mode that is associated with the oxygen vibrations along the ab-plane exhibits a redshift, consistent with the lattice dilatation observed in the x-ray diffraction data; (ii) the 106 cm-1 peak belongs to the lattice origin, rather than the two-magnon continuum assigned by Phys. Rev. B 69, 104421 (2004).; (iii) the 492 cm-1 phonon mode of 7 % Zn doped sample shows a slight redshift below the magnetic phase transition of 14 K, indicating a spin-phonon coupling.
Second, room-temperature Raman-scattering spectrum of Ho0.01Mn0.99S shows four phonon modes at about 135 cm-1, 227 cm-1, 333 cm-1 and 585 cm-1. With increasing Ho content, there are also three important features to these spectra: (i) the 333 cm-1 and 585 cm-1 phonon modes exhibit a redshift due the larger ionic size of Ho; (ii) diffusive-type Raman-scattering response appears at low temperatures, which is likely related with the carrier collision-dominated mechanism; (iii) the spectral weight of the 333 cm-1 and 585 cm-1 phonon modes decreases at about 350 K, 500 K, and 620 K. These results correlate with the variations of electric resistivity and the lattice constant, suggesting the possibility of orbital-ordering, or charge-ordering phenomena.

並列關鍵字

LiCu2O2 ； HoxMn1-xS ； Raman-scattering spectra ； orbital-ordering ； diffusive scattering

參考文獻

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