幾何不穩態四面體自旋系統銅鍗氧氯或銅鍗氧溴被認為具有磁介電效應的特性，在銅鍗氧氯的樣品發現相轉變溫度TN為18.5 K，此相變為3維的反鐵磁有序，並且在施加磁場最大至90 kOe的介電係數量測中發現低溫區18.5 K的峰值會隨著磁場而降低，而在銅鍗氧溴的樣品它的相轉變溫度To為11.5 K 但是有很多不尋常的特性在其中，而且施加最大磁場至90 kOe的介電係數量測中發現低溫區30 K的峰值會隨著磁場而降低。
隨之而來有一個明顯的鐵電有序在銅鍗氧氯的尼爾變溫度和銅鍗氧溴的相轉變溫度同時發生，而鐵電性常被歸因於Te4+ 孤對電子的極性造成，磁介電效應被認為和四面型不穩態群集裡的交互作用力有關。

An intriguing magnetodielectric (MD) behavior is observed in geometrically frustrated spin-tetrahedral systems Cu2Te2O5X2 (X = Cl and Br). While the phase transition observed in the Cl-system at TN=18.5 K is consistent with 3D antiferromagnetic ordering, the phase transition at To=11.5 K in the Br-system has several unusual features. Concomitantly, a pronounced ferroelectric ordering is observed coinciding with TN of Cl-system and To of Br-system. At the highest applied magnetic field 90 kOe, the temperature dependent dielectric behavior with almost frequency independent well defined at TN~18.5 K are decrease compared with that at zero field for Cl-system, and at the highest applied magnetic field 90 kOe, the temperature dependent dielectric behavior with almost frequency independent well defined at Tm~30 K are decrease compared with that at zero field for Br-system. The ferroelectricity is ascribed to the polarization of the Te4+ lone-pair electrons, while the MD effect is argued to be due to exchange interaction involving frustrated tetramer clusters and intercluster exchange bridges.

目錄
致謝 I
論文摘要 II
ABSTRACT III
目錄 IV
圖目錄 V
第一章：簡介 1
1.1一般介紹 1
1.2幾何自旋不穩態系統(Geometrical spin frustrated system) 2
1.3 銅鍗氧氯和銅鍗氧溴系統(Cu2Te2O5X2 system, X＝Cl and Br) 5
1.3.1 結構 5
1.3.2 磁性量測 6
1.3.3 比熱量測 7
1.3.4 中子繞射研究 8
1.4 動機 9
第二章：實驗儀器與方法 10
2.1樣品製備及分析 10
2.2 超導量子干涉儀 10
2.2.1 超導量子干涉儀原理 10
2.2.2 量測 14
2.3 介電係數量測 16
2.3.1 儀器原理 16
2.3.2 量測方法 18
第三章：結果與討論 19
3.1 磁特性 19
3.2介電特性 25
第四章：結論 41
參考文獻 42

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