| 摘要: | 熱電材料GeTe屬於P型半導體，是一種會因溫度改變而發生結構相變的材料，其在中溫區(300~600 K)至高溫區(> 600 K)的範圍中具有不錯的zT值，若摻雜Sb及Bi會使zT值(優質係數)變大，同時在(Ge0.86Sb0.08Bi0.06)Te這種Sb/Bi摻雜比例下，其在高溫區的zT值會大於2，是一個具有潛力的熱電材料之一。
在本研究中，將著重於探討(Ge0.86Sb0.08Bi0.06)Te此材料內的聲子動力行為，這是利用澳洲ANSTO的冷中子三軸散射儀(SIKA)進行的實驗研究。首先，會先利用SIKA進行此材料的中子彈性散射實驗，以判斷結構相的轉變溫度。之後，進行此材料於200 K、400 K、500 K、680 K及800 K的中子非彈性散射實驗，並繪製各溫度下的中子色散圖(即波向量-頻率關係圖或波向量-能量關係圖)，以看此材料在各溫度內的聲子動力行為。
針對聲子動力行為的分析，是透過初始能量(Initial energy, E0)、能隙(Energy gap, Eg)、聲子諧振能量(Phonon harmonic energy, Eh0)、非諧振聲子-聲子散射能量(Anharmonic phonon-phonon scattering energy, Ep-p)、電子-聲子散射能量(Electron-phonon scattering energy, Ee-p)四個參數進行擬合分析，並藉由這四個參數與溫度的關係來獲得熱效應所引發聲子動力行為轉變的資訊。;The thermoelectric material GeTe is a P-type semiconductor that undergoes a structural phase transition when the temperature changes. It exhibits good zT values (a measure of thermoelectric quality) in the mid-temperature range (300~600 K) to high-temperature range (> 600 K). Doping with Sb and Bi enhances the zT value; for instance, in the (Ge0.86Sb0.08Bi0.06)Te material, the zT value exceeds 2 in the high-temperature range, making it a promising thermoelectric material.
In this study, we focus on the phonon dynamics within the (Ge0.86Sb0.08Bi0.06)Te material, utilizing the cold neutron triple-axis spectrometer (SIKA) at Australia′s ANSTO for experimental research. Initially, neutron elastic scattering experiments are conducted using SIKA to determine the phase transition temperatures of the material. Subsequently, neutron inelastic scattering experiments are performed at temperatures of 200 K, 400 K, 500 K, 680 K, and 800 K. Neutron dispersion diagrams (i.e., wave vector-frequency or wave vector-energy relationships) are plotted to observe the phonon dynamics at these temperatures.
The analysis of phonon dynamics involves fitting four parameters: background energy (E0), energy gap (E¬g), phonon harmonic energy (Eh0), anharmonic phonon-phonon scattering energy (Ep-p), and electron-phonon scattering energy (Ee-p). The relationship between these parameters and temperature provides insights into the phonon dynamic changes induced by thermal effects. |
