本論文針對鈣鈦礦La0.80Sr0.20MnO3摻雜鹼金元素系列樣品，於10至400 K的溫度區間進行磁化率(χ)、比熱(CP)、電阻率(ρ)、熱電勢(S)以及熱導率(κ)等物理性質量測，以探討改變摻雜鹼金離子(La3+：1.032 Å、Sr2+：1.18 Å、Na+：1.02 Å、K+：1.38 Å)對上述物理性質的影響。磁性量測結果顯示樣品在高溫區呈現為順磁性，在低溫區則轉變磁有序的鐵磁性，且樣品的順磁-鐵磁相變溫度(居禮溫度，Tc)隨著鈉、鉀的摻雜增加而降低。此外，於比熱與電阻率的金屬轉絕緣相變溫度(TMI)亦可觀察到相同的趨勢。
比熱的量測結果顯示，鹼金元素的摻雜會使熵值變化量降低，說明摻雜半徑減小會減弱樣品鐵磁態磁矩間的交互作用力，此與磁化率量測結果有相同趨勢。此系列樣品皆由低溫金屬性質轉為高溫絕緣性質，並由電阻率低溫擬合結果得知，在低溫順磁金屬區段，系列樣品電阻率主要貢獻皆為電子-電子散射。熱電勢隨著溫度上升，其數值皆由正值轉為負值，顯示此系列樣品主要傳導載子由電洞轉為電子，並隨著鹼金離子的摻雜，熱電勢值有上升的趨勢。此外，熱電勢與電阻率高溫區段分析結果顯示，此系列樣品之傳輸機制均符合小極化子模型。熱導率部分，隨著鈉、鉀離子摻雜，於低溫鐵磁區段熱傳導率有明顯降低的趨勢，說明摻雜鈉、鉀離子半徑不同所造成的晶格扭曲，會造成聲子熱傳導散射機率上升。而高溫順磁區段，由於熱激發的極化子亦參與熱傳導，導致熱導率隨溫度上升而增加。

In this thesis, we report the investigation of the temperature-dependent magnetization (χ), specific heat (CP), electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) on the alkali-doped (Na and K) La0.80Sr0.20MnO3 manganite compounds in the temperature range of 10 K to 400 K. It was observed from these measurements that with increasing sodium content both the metal-insulator transition temperature (TMI) and the ferromagnetic-paramagnetic (TC) transition temperature shift towards to lower temperatures. It is found that the values of electrical resistivity increase with increasing Na content. This is attributed to the fact that the substitution of the larger Sr ions (1.18 Å) by smaller Na ions (1.02 Å) induces the distortion of MnO6 octahedra, leading to a weakening of double-exchange interaction. From specific heat measurements, the entropy change decreases slightly with increasing sodium content, indicating that the strength of magnetic ordering decreases with Na substitution, which is consistent with the magnetization measurements. The studied samples show a crossover around 200 K from a small positive value of Seebeck coefficient at low temperatures to a negative value at higher temperatures. This sign reversal is due to the change in the nature of charge carriers from holes to electrons. It is noted that the Seebeck coefficient of La0.80Na0.20MnO3 remain positive over the entire temperature range, this behavior is most likely due to an enhancement of the holes contribution with sodium substitution.
Analyses of electrical resistivity and Seebeck coefficient data confirm that the small polaron hopping (SPH) model is operative in the high-temperature insulating region, consistent with the positive slope in temperature-dependent thermal conductivity at high temperatures.

致謝 I
摘要 III
Abstract V
目錄 VII
圖目錄 XI
表目錄 XV
第一章 前言 1
1-1 簡介 1
1-2 實驗動機及目的 3
第二章 材料特性研究 5
2-1 磁性理論 5
2-2 磁性種類 6
2-2-1 順磁性(Paramagnetism) 7
2-2-2 逆磁性(Diamagnetism) 9
2-2-3 鐵磁性(Ferromagnetism) 10
2-2-4 反鐵磁性(Antiferromagnetism) 12
2-2-5 亞鐵磁性(Ferrimagnetism) 13
2-3 磁阻現象(Magnetoresistance) 14
2-4 鈣鈦礦(Perovskite) 17
2-5 雙交換模型(Double Exchange Model) 20
2-6 Jahn-Teller Distortion 24
2-7 極化子 26
2-7-1 小極化子跳躍模型(Small Polaron Hopping Model) 27
第三章 實驗原理 29
3-1 電阻率 29
3-2 熱傳導率 33
3-2-1 聲子對熱傳導的影響 34
3-2-2 電子對熱傳導的影響 37
3-3 比熱 39
3-3-1 電子比熱 39
3-3-2 聲子比熱 40
3-3-3 磁性比熱 41
第四章 實驗方法 44
4-1 量測系統與方法 44
4-1-1 低溫冷卻系統 44
4-1-2 電阻率量測方法 46
4-1-3 熱傳導率的量測 47
4-1-4 Seebeck 係數量測 49
4-2 實驗控制程式 50
4-3 比熱量測方法 57
4-3-1 運作頻率之選擇方法 63
4-4 磁性量測方法 65
4-4-1 超導量子干涉磁量儀 65
4-4-2 磁化強度對溫度(M-T)的量測 67
4-4-3 磁化強度對外加磁場(M-H)的量測 67
第五章 實驗結果與分析 67
5-1 磁化強度對溫度的量測分析 67
5-2 比熱對溫度的量測分析 70
5-3 電阻率對溫度的量測分析 73
5-4 熱電係數對溫度的量測分析 79
5-5 熱導率對溫度的量測分析 84
第六章 結論 87
參考文獻 89

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