釩酸鹽氧化物因其幾何結構與電子特性之特殊性引起部分學者關注，近期也有研究指出多鐵性材料TM2V2O7（TM =Cu, Co and Ni）由於晶體結構和磁特性所造成的磁驅動電的現象。材料Co2V2O7晶體結構為單斜晶對稱結構，在Co2V2O7中，兩個Co2+O6陽離子八面體共邊連接，且沿c軸排列成鋸齒鏈，鏈與鏈之間又被非磁性的(V2O7)4-離子分開，導致一維不穩態反鐵磁序。而Cu2V2O7有三種不同的多晶型態，較穩定的兩種為: (I) α- Cu2V2O7結構，為斜方與非中心對稱；與(II) - Cu2V2O7結構，為單斜與中心對稱。α-Cu2V2O7中，Cu2+O5多面體形成交聯鏈網絡，與Co2V2O7一樣，Cu2+O5排成的一條條長鏈被不具磁性的(V2O7)4-陰離子分開，使系統發生Dzyaloshinskii-Moriya (DM)交互作用，並引起弱鐵磁性。本研究摻雜了低濃度(5%)的磁性元素(Co)和非磁性元素(Zn和Ga)，以了解摻雜效應對α-Cu2V2O7在結構、磁性和介電性質方面的影響。我們的磁化數據清楚的表示不同元素的摻雜確實影響α-Cu2V2O7的磁特性。特別在α-Cu2V2O7中摻雜磁性元素Co對磁特性有顯著的影響，而非磁性元素的摻雜並未改變結構中的DM交互作用。

Vanadates oxide materials exhibit a variety of functional properties whose origin is closely related to the structural and electronic peculiarities of the compounds. Recently, in the vanadatesTM2V2O7 (TM = Cu, Co and Ni), a magnetically driven ferroelectric phenomena has been reported. The multiferroic ordering of these system closely connected with the crystal structure and their magnetic properties. The crystallographic structure for Co2V2O7 exhibits a dichromate structure with crystallizes in a monoclinic symmetry, whereas Cu2V2O7 crystallizes in two different polymorphs (I) α-structure, that is orthorhombic and noncentrosymmetric, and the (II) -phase that is monoclinic and centrosymmetric. In Co2V2O7, two Co2+O6 cations octahedral connected via edge sharing and forms the zigzag chains along c-axis and chains are separated by nonmagnetic (V2O7)4- groups that lead to frustrated one dimensional antiferromagnetic ordering. On the other hand, in α-Cu2V2O7, Cu2+O5 polyhedral form the cross-linking chain network which are separated by (V2O7)4- anion units makes system a weak ferromagnet ground state induced by Dzyaloshinskii-Moriya (DM) interaction. In these present study, we are doping the small concentration (5%) of magnetic (Co) and nonmagnetic (Zn and Ga) elements to understand the effect of doping on the structural magnetic and dielectric properties of α-Cu2V2O7. Our magnetization data clearly indicates that the Co doping significantly modifies the ground state magnetic property by invoking the frustration. However nonmagnetic elements does not show much influence on the strength of DM interaction of α-Cu2V2O7. We believe local structural modulation by chemical doping with different doping element might alters the magnetic ground state of α-Cu2V2O7.

論文審定書+i
誌謝+iii
論文摘要+iv
Abstract+v
目錄+vii
圖目錄+ix
表目錄+xi
第一章 簡介+1
1-1 多鐵性材料介紹與磁性簡介+1
1-2 超交換作用+6
1-3 材料介紹+8
1-3-1 Cu2V2O7簡介+8
1-3-2 Co2V2O7簡介+19
1-4 研究動機+22
第二章 實驗儀器與方法+23
2-1 X光繞射分析儀+23
2-2磁性量測儀器及量測方法+25
2-3 CLOSE CYCLE REFRIGERATOR (CCR) SYSTEM+30
2-4 X光吸收近邊緣結構光譜+31
第三章 實驗結果與討論+33
3-1 樣品製備+33
3-2 X-RAY結構分析+36
3-3 磁性與電性實驗結果與討論+42
3-3-1 磁性實驗量測結果+42
3-3-2 電性實驗量測結果+49
3-4 XANES實驗結果+52
結論+55
參考文獻+56

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