我們主要的課題是去研究自旋頓挫態ZnV2O4之磁性與介電性特性，並去尋找此材料是否存在多鐵性性質。我們利用固態反應法去製作ZnV2O4，過程中以抽真空方式去進行不同燒結溫度下的樣品製作，所得樣品以X-Ray去檢測樣品純度與品質，我們發現燒結溫度800度比900度佳。由文獻我們可知ZnV2O4是尖晶石結構，且是一立方晶系結構。我們利用GSAS軟體去擬合我們所得之X繞射圖譜，得到晶格常數a=8.31 Å。由我們所量測之磁性結果，並無明顯發現有著反鐵磁相轉變，而在溫度約52K附近可能是一個結構相轉變(立方結構到四方結構)，以及在溫度約9K附近有一類似自旋玻璃態的行為發生。在介電量測當中，我們發現在溫度約50K有一介電係數瞬間往下之階梯狀曲線，其曲線會隨頻率增大而往高溫區移動，在介電圖譜當中，沒顯現出有著鐵電性的特性，故我們初步認定ZnV2O4不具有多鐵性質的材料。另外，我們發現ZnV2O4有著很大的介電係數，並由阻抗頻譜中，頻譜與電模量隨著頻率之變化，我們可以看出晶粒與晶界之電的異質性。所以巨大介電常數可以歸因於麥克斯韋 - 瓦格納界面極化所造成。

The purpose of this work is to study the correlation of magnetic and dielectric property in the spin-frustrated ZnV2O4 spinel oxide. The geometrically frustrated spinel ZnV2O4 prepared using solid state reaction method followed by annealing at different temperatures. X-ray diffraction (XRD) has been employed to check the phase purity of the sample. From XRD analysis, we found that, with increase of sintering temperature from 800℃ to 900℃ the secondary phases in appeared in XRD spectrum. Riveted analysis using GSAS software has been employed for structural refinement. The refinement fit to cubic crystal structure with Fd-3m space group with lattice parameter a = 8.31Å. Magnetization measurements reveal multiple magnetic transitions corresponding to cubic to tetragonal structural transition (52 K) and spin-glass-like behavior (9 K) respectively.
Among the dielectric measurement, huge permittivity with huge frequency dispersion has been noticed. With decreasing temperature, dielectric permittivity exhibit step like drop and this drop shift to high temperature for higher frequencies. And we did not find ferroelectric signature in dielectric spectrum. Therefore, we initially exclude the possibility of multiferroics of ZnV2O4. Moreover, frequency-impedance diagrams and modulus spectrum reveal the electrical heterogeneity across the grain and grain boundary. Based on our results, we attributed the huge dielectric constant to Maxwell - Wagner interfacial polarization.

致謝 i
論文摘要 ii
Abstract iii
目錄 iv
圖目錄 vi
第一章 簡介 1
1-1 多鐵性 1
1-2 自旋頓挫態系統 6
1-3 ZnV2O4 之已發表物理特性 12
1-4 研究動機 20
第二章 實驗儀器 21
2-1 XRD 繞射儀 21
2-2 超導量子干涉儀 23
2-3 介電性量測與電阻率量測 29
2-4 掃描電子顯微鏡 31
第三章 結果與討論 32
3-1 ZnV2O4 樣品製備 32
3-2 樣品純度分析 38
3-3 X 光能譜分析儀 39
3-4 磁性分析 41
3-5 介電性分析 48
第四章 結論 60
參考文獻 63

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