四咪唑硫酸銅晶體的固態相變遲滯行為

Hysteresis Behavior During the Solid Phase Transition of Cu(imidazole)4SO4

劉建宏(Chien-Hung Liu)

指導教授 ： 曾炳墝 ； 劉陵崗

國立中正大學/理學院/化學暨生物化學系/碩士(2014年)

摘要

我們合成出Cu(im)4SO4，並對其進行相變實驗。Cu(im)4SO4在常溫下的結構是六配位銅中心與硫酸根交互呈現的一維鏈狀結構，但是在低溫下，Cu(im)4SO4晶體會產生相變，有部分銅氧鍵產生斷裂，造成每四個銅為一個單元，外部兩個銅為五配位，內部兩個銅為六配位，使得結構中有兩種配位形式的銅。
比較特別的是，Cu(im)4SO4在相變行為中，會產生遲滯的現象。透過變溫X光單晶繞射(single crystal X-ray diffraction)，發現在降溫過程中晶體相變溫度在183K，但是在升溫過程中晶體的相變溫度在187K，發生了遲滯現象，這樣的行為在相變裡並不常見。
從變溫結構解析研究中我們發現，在降溫程序，晶體相變是透過兩個步驟完成，高溫相晶系會先變成低溫相晶系，隨後銅氧鍵才會斷裂；但在升溫程序，回復至高溫相，晶系與銅氧鍵生成，為一步驟完成。我們認為這是造成遲滯的原因。
此外，我們也對Cu(im)4SO4進行熱微差掃描分析(differential scanning calorimetry)，在降溫過程中相變溫度在182K，而在升溫過程中相變溫度在189K，同樣觀測到遲滯行為。對Cu(im)4SO4而言，在高壓環境與低壓環境下，拉曼光譜會發生差異。升壓相變與降壓相變的數據也與遲滯行為相符合。

關鍵字

鑽石砧加壓器 ； 四咪唑硫酸銅 ； 遲滯行為

並列摘要

Single crystals of Cu(im)4SO4 exhibited a solid phase transition with an interesting hysteresis behavior in response to temperature. Only one unique type of copper has been found in the high temperature phase of the single crystal. Yet there are two different types of copper in the low temperature phase of the single crystal interestingly.
The high temperature phase could be reversibly converted to the low temperature phase such that the crystal changes phase at 183K during the cooling process, nonetheless, the reverse phase change occurs at 187K during the heating process, evidenced in X-ray crystallographic studies.
The Cu(im)4SO4 crystals changed from high temperature phase to low temperature phase, followed by the rupture of 2 Cu-O bond from linear segment of every [-O-Cu-OSO2-]4 , upon cooling to lower than the phase transition point. This is a two-step process.
On the other hand, the low temperature phase changed to high temperature phase with concurrent Cu-O bond reformation in the heating process. This is a one-step process. It could possibly be the reason to exhibit the hysteresis behavior.
In addition, we also used differential scanning calorimetry to evidence hysteresis behavior. We found, in agreement to the above observation that the crystal changes phase at high pressure to give a high pressure phase which is different from the low pressure phase.

並列關鍵字

diamond anvil cell ； hysteresis behavior

參考文獻

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