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研究生：	葉庭君 Yeh, Ting-Chun
論文名稱：	鈣鈦礦結構錫酸鍶高溫相變之拉曼研究 Raman Study of High-Temperature Phase Transitions in Perovskite SrSnO3
指導教授：	龔慧貞 Kung, Hui-Chen
學位類別：	碩士 Master
系所名稱：	理學院 - 地球科學系 Department of Earth Sciences
論文出版年：	2025
畢業學年度：	113
語文別：	英文
論文頁數：	104
中文關鍵詞：	鈣鈦礦結構錫酸鍶、晶格動力學、高溫相變、非諧性、偏光拉曼光譜
外文關鍵詞：	SrSnO3 Perovskite, Lattice dynamics, High-temperature phase transition, Anharmonicity, Polarized Raman spectroscopy
相關次數：	點閱：39 下載：0
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本研究旨在探討鈣鈦礦結構錫酸鍶（SrSnO3）在高溫結構演變下的晶格動力學行為。
透過國家同步輻射研究中心提供之高解析粉末繞射技術，在常溫至 1173 K 測量晶格結構演變；Rietveld 結構精修結果顯示，SrSnO3 在約 853 K 附近歷經從斜方晶系 Pbnm 到 Ibmm 的對稱性轉變，隨後在約 1023 K 進一步相變為四方晶系 I4/mcm。此外，在 Pbnm 至 Ibmm 的相變之前，晶格參數開始在約 623 K 發生異常的發散，此特徵在先前的文獻報導中被指出是由 SnO6 八面體的有序–無序轉變所引起。
另一方面，成功合成 SrSnO3 單晶並進行偏光拉曼光譜測量，沿著各個晶軸方向取得振動模態訊號，輔以 DFT 理計算，指認出 24 個拉曼振動模態（7Ag + 5B1g + 7B2g + 5B3g）中的 13 個。透過高溫單晶偏光拉曼實驗，進一步揭示了振動模態的行為與結構對稱性變化之間的關聯，包括強度變化、紅移與寬化等現象，補足了前人在粉末拉曼研究中缺乏各向異性資訊的限制。Bg 模態在高溫下維持穩定的峰型，且在相變邊界附近，頻率與峰寬有明顯的趨勢變化，尤其在進入四方相（I4/mcm）時，頻率紅移明顯減緩。Ag 模態中，ν6（167.98 cm⁻¹）在 Pbnm 相展現非線性的軟模行為，並在強度變化上呈現明顯的非均向性；而 ν7 模態（221.56 cm⁻¹）則在 623–723 K 之間表現出異常的散射強度增加，此現象可能與結構中 SnO6 八面體的有序–無序擾動有關。
基於高溫拉曼光譜的分析結果，估算出 SrSnO3 各個振動模態的 Grüneisen 參數，普遍大於 2；該材料在宏觀上整體的Grüneisen參數為 γbulk = 1.6，與 MgSiO3 相近。這些結果提供了鈣鈦礦晶格動力學行為的重要參考，對地球科學研究與材料科學之應用皆具有重要的參考價值。

This study investigates the structural evolution and lattice dynamics of SrSnO3.
Lattice structural changes were obtained via HT-PXRD from room temperature to 1173 K; Rietveld refinement verified a symmetry transition from orthorhombic Pbnm to Ibmm near 853 K, followed by a transition to tetragonal I4/mcm around 1023 K. Additionally, an anomalous divergence of cell parameters before the Pbnm–Ibmm transition was consistent with a previously reported order–disorder transition beginning around 623 K.
Polarized Raman spectroscopy, conducted on orientation-identified single crystals to acquire spectra along each crystallographic axis, supported by DFT calculations, enabled the assignment of 13 out of the 24 predicted Raman-active vibrational modes (7Ag + 5B1g + 7B2g + 5B3g). Polarized HT-Raman analysis of single crystals revealed correlations between mode behaviors and structural changes, including variations in mode intensity, frequency shift, and line broadening, thereby overcoming limitations of the previously reported powder Raman study, which lacks anisotropic information. For Ag modes, most follow linear trends, while ν6 (167.98 cm⁻¹) exhibited nonlinear soft-mode behavior within the Pbnm phase and displayed pronounced intensity anisotropy along different crystallographic axes; mode ν7 (221.56 cm⁻¹) showed an anomalous intensity increase between 623 and 723 K, likely related to the SnO6 octahedral order–disorder fluctuations. The Bg modes maintained stable peak shapes at high temperatures while exhibiting noticeable changes in frequency and bandwidth near phase boundaries, along with slowed frequency redshifts in the tetragonal phase.
Mode-specific isobaric Grüneisen parameters were estimated to generally exceed 2; the bulk Grüneisen parameter (γbulk = 1.6), comparable to that of MgSiO3, provides an important reference for investigating anharmonicity in perovskites and offers valuable insights for both geoscientific research and materials-science applications.

Abstract	i
摘要	iii
誌謝	iv
Contents	vi
List of Figures	viii
List of Tables	x
Chapter 1 Introduction	1
1.1 Perovskite Structure	1
1.2 SrSnO₃ Perovskite	2
1.2.1 Structural Transitions	2
1.2.2 High-Temperature Raman Study	3
1.3 Lattice Dynamics and Anharmonicity	4
Chapter 2 Method	12
2.1 Sample Preparation	12
2.1.1 Systhesization	12
2.1.2 Sample Identification	13
2.2 High-Temperature X-Ray Diffraction	14
2.2.1 Experimental	14
2.2.2 Data Refinement	15
2.3 Raman Spectroscopy	16
2.3.1 Polarized Raman Spectroscopy	17
2.3.2 High-Temperature Raman Experiment	18
2.3.3 Data Analysis	18
2.4 DFT calculation	18
Chapter 3 Results	28
3.1 Sample	28
3.1.1 Powder	28
3.1.2 Single-Crystal	29
3.2 High-Temperature X-Ray Diffraction	29
3.2.1 Temperature-Dependent Diffraction	29
3.2.2 Lattice Evolution and Symmetry Transitions	30
3.3 Raman Analysis	32
3.3.1 DFT Calculation	32
3.3.2 Powder Raman Spectroscopy	33
3.3.3 Single-Crystal Raman Measurement and Mode Assignment	34
3.3.4 High-Temperature Single-Crystal Raman Spectra	35
3.4 Thermally Induced Detwinning	38
Chapter 4 Discussion	74
4.1 Structural Stability at High Temperature	74
4.2 Temperature-Driven Raman Behaviour	74
4.3 Anharmonicity and Grüneisen Parameter	76
4.4 Applications and Outlook	77
Chapter 5 Conclusion	82
References	83
Appendix 1 EDS Chemical Analysis	86
Appendix 2 Additional DFT-Calculated Raman Mode Information	88
                                    

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