Sr2SiO4的低、高溫相結構之間為一階熱力學特徵的位移相變，但卻被發現高溫相在合成粉末中可被保留至室溫環境中，其原因仍是未知的。本研究藉由固相反應法及溶膠-凝膠法在不同煆燒條件下合成Sr2SiO4一系列粉末樣品，並觀察樣品晶粒尺寸大小與結晶結構關係。同時以低、高溫相樣品於適當條件下進行現地高溫實驗及熱處理實驗，觀察其受溫度影響時所造成的結構變化，探討Sr2SiO4結構穩定因素及其高溫行為。
溶膠-凝膠法合成結果發現至少必須1400℃才能形成Sr2SiO4，且其產物皆以低溫相結構為主。然而，固相反應法中在900℃即可獲得Sr2SiO4，且發現低溫相的比例會隨著煆燒溫度增加與時間增長而逐漸增加，而高溫相漸減少。兩種製程粉末結果在SEM影像中，可明顯發現溶膠-凝膠法合成樣品晶粒會大於固相反應法樣品。搭配現地高溫實驗與熱處理實驗結果認為當Sr2SiO4晶粒越小、降溫速率越快的情況下，越有利於高溫相被保留。認為高溫相Sr2SiO4被保留至室溫下是受控於兩個因素，熱遲滯效應是由於其相變特徵為一階相變，晶粒尺寸效應則會影響熱遲滯現象的程度。由於小晶粒中晶格內應變程度較大晶粒者嚴重，使其在降溫過程中須克服更多能量，加上Sr2SiO4本身之高、低溫相轉換的相變溫度已非常低(約85℃)，而導致小晶粒中的原子在室溫下無法回到低溫相的平衡位置，因而保留了高溫相結構。從SEM影像推測高溫相Sr2SiO4被保留的臨界尺寸大約在0.7~1μm左右，表示晶粒尺寸影響其物質結晶結構的現象不只出現在奈米尺度下，也會發生於次微米尺度中。
本研究也首次提出Sr2SiO4之熱膨脹係數，雖然無法以其判斷α'L (調整型結構)和α'H，但發現其隨溫度的變化程度會遠較同族的Mg2SiO4大。

The phase transition between low temperature (LT) and high temperature (HT) phase of Sr2SiO4 is displacive with 1st-order thermodynamic characteristic. However, the HT phase was found to be stable at room temperature in synthesized powder samples with the reasons remain unknown.
In this study, by synthesizing powder samples via solid state reaction and sol-gel method with series of sintering condition to observe the relationship between grain size and crystal structure. Also, LT and HT phase samples were examined via in-situ high temperature and thermal treatment experiments to observe the structure change through variation of temperature to study the phase stabilization factors of Sr2SiO4 and its high temperature behavior.
The synthesis results from sol-gel method showed the Sr2SiO4 phase cannot be obtained till up to 1400℃ and which were all LT phase dominant. However, Sr2SiO4products can be synthesized as low as 900℃ in solid state reaction and were noticed the amounts of LT phase would increase with increasing synthesis temperature or period of time. The SEM images indicated that the grain size of sol-gel method products is larger than those from solid state reaction. With in-situ high temperature and thermal treatment experiments, the HT phase is tend to appear with smaller grain size and by faster cooling rate.
The factors of stabilization of HT phase at room temperature are suggested to affect by thermal hysteresis and grain size effect. The former is its intrinsic property and is affected by the latter at some extent. Those smaller grains have larger curvature which makes it have larger strain in structure. This leads to smaller grains cannot overcome the energy barrier to transform back to its equilibrium positions (LT phase). From SEM images, the critical grain size for stabilizing HT phase is about 0.7~1 μm and propose that this effect doesn’t only occur in nano-scale but also in sub-micron scale.
For the first time, we have the thermal expansion data of Sr2SiO4. Though we can’t tell the difference from α'L(modulated structure) and α'H now, we discover the thermal expansion behavior is very different from similar material - Mg2SiO4.

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