頑火輝石(Enstatite,MgSiO3)是斜方晶系的單鍊狀矽酸鹽礦物，也是上部地函最重要的組成礦物之一，其熱力學參數和地震波速有密切關聯。天然環境中的輝石結構中可能含有鋁(Al2O3 wt% ≤ 6.0)且鋁離子可能取代其結構中鎂離子位置(M site)或矽離子位置(T site)，目前卻無人針對不同鋁含量摻雜對該材料的拉曼行為影響進行調查及討論。因此本研究主要使用高溫拉曼(23℃至 1000℃)測量 0.0 至 17.2 wt% Al2O3 輝石單晶，觀察其拉曼振動頻率隨溫度的變化趨勢 000，並利用振動頻率推算所有樣品的格呂奈森參數(γ)、非諧性(a)以及熱容量(CP)。
本研究於高溫高壓環境下合成 0.0 至 17.2 wt% Al2O3 輝石單晶，並使用 X-Ray 單晶繞射來鑑定樣品空間群以及獲得晶格常數，使用 EDS 化學分析來分析樣品中 Al2O3 wt%。本研究除了以高溫拉曼實驗為主，還以低溫拉曼測量(-196℃至 400℃)探討振動模寬化主要因素。本研究也藉由高壓拉曼(0.0GPa 至20.0GPa)輔助實驗來探討壓力對含鋁輝石格呂奈森參數的影響。
研究結果顯示當直輝石 Al2O3 wt%高達 17.2 時，其空間群仍保存為 Pbca，但鋁離子摻雜會使其晶格體積減少。高溫拉曼測量結果指出所有輝石振動頻率變化趨勢大多較接近線性，純鎂(0.0 wt% Al2O3)樣品 82cm-1 振動頻率以及 Al2O3 10.0 wt% 樣品82、133、205、343、680、1030cm-1 振動頻率隨溫度變化趨勢則呈現顯著非線性。純鎂樣品 82cm-1 振動頻率非線性特徵可能反映出該振動模的軟化現象，而 10.0 wt%樣品振動模的非線性特徵可能反映出這些振動模的非諧性。熱力學參數推算結果亦指出 Al2O3 10.0 wt%樣品熱容量受到的非諧效應影響最大，本研究認為這可能是因為鋁離子在該樣品結構中取代 M site 及 T site 的比例有別於其他樣品，因此建議未來針對不同鋁含量輝石的鋁離子分佈趨勢進行探討。

Synthetic orthoenstatite (MgSiO3) with different aluminum content (0.0-17.2 wt% Al2O3) are used to investigate the effect of Al3+ coupling into the crystal structure. The chemical analysis of these samples are confirmed using EDS and the crystal structure of these samples are refined from single crystal X-ray diffraction. Raman spectra under various conditions (-194 to 1000 ℃ or up to 20 GPa) were acquired and analyzed. The Raman behavior under high temperatures are further used for thermodynamic parameter estimation, such as Gruneisen parameter, anharmonicity, and heat capacity.
While most enstatite samples exhibit linear changes in vibrational mode frequencies with rising temperature, 0.0 wt% Al2O3 sample at 82 cm-1 and 10.0 wt% Al2O3 sample at 82, 133, 205, 343, 680, and 1030 cm-1exhibit nonlinear trends with temperature. The nonlinear characteristics of 0.0 wt% Al2O3 sample at 82 cm-1 may reflect the softening of this vibrational mode, while the trends of the 10.0 wt% Al2O3 sample may indicate the anharmonicity of these vibrational modes. Although the estimated Gruneisen parameter and anharmonicity does not seem to have systematic changes with Al3+ content, the heat capacity exhibits noteworthy differences. Particularly, the 10.0 wt% Al2O3 sample shows the largest difference between heat capacities estimated with and without considering anharmonicity, implying a significant impact in this case. The distinctive distribution of Al3+ in the 10 wt% sample, as determined through chemical analysis and single-crystal X-ray diffraction, suggests that abnormalities in Raman behavior and thermodynamic properties may be attributed to the specific Al3+ distribution in this sample.

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