摻雜Sb/Bi對熱電材料Ge0.86Sb0.08Bi0.06Te熱導率的影響

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題名:	摻雜Sb/Bi對熱電材料Ge0.86Sb0.08Bi0.06Te熱導率的影響
作者:	凌慈茵;Ling, Tzu-Yin
貢獻者:	物理學系
關鍵詞:	熱電材料;聲子
日期:	2021-06-30
上傳時間:	2021-12-07 12:01:07 (UTC+8)
出版者:	國立中央大學
摘要:	GeTe是硫屬化物，具有半金屬傳導與鐵電性，鐵電溫度為670 K，因其具有相較於其他IV-VI化合物有著較高的電導率與很高的熱導率（8W/m-1K-1），適合做為熱電材料。然而GeTe中具有大量的Ge空位，導致Seebeck係數降低並影響熱電優值，因此若能透過參雜降低其空穴濃度，便可提升其熱電性能。由其他研究已知在GeTe中參雜Sb與Bi會影響電子與聲子並改善熱電性值，因此在本次實驗中，將著重於探討樣品摻雜後參雜物對聲子散射的影響和降低熱導率的機制。我們使用澳洲的Ansto冷中子三軸散射儀SIKA進行非彈性中子散射測量，首先量測溫度範圍300 K至710 K的中子彈性散射圖，發現樣品在625 K至710 K溫度區間內由R3m相轉移到Fm3 ?m相，其中兩個結構相有共存的現象。此外，我們繪製出Ge0.86Sb0.08Bi0.06Te在溫度區間300 K至680 K的聲子色散圖，透過擬合得到布里淵區邊界晶格簡諧能量Eh、電子-聲子相互作用能量Ee-p與非諧性能量Ea，發現在此溫度區間內，出現晶格非諧性以及非常強的電子-聲子相互作用；除此之外，由於電子-聲子散射較強，導致了聲子能量軟化。其次透過擬合得到聲子色散，聲子壽命，和傳播長度等性質，得知在參雜後樣品具有較短的聲子壽命與聲子傳播長度，加上群速度在大q值處會轉變為負值，這些因素都限制了熱傳輸並降低Ge0.86Sb0.08Bi0.06Te的晶格熱傳導率，從而增加了該樣品的ZT值。 ;GeTe is a chalcogenide with semi-metallic conductivity and ferroelectricity. The ferroelectric temperature is 670 K. Because it has higher electrical conductivity and higher thermal conductivity than other IV-VI compounds (8W/m -1K-1), it’s suitable as a thermoelectric material. However, there are a large number of Ge vacancies in GeTe which decreases the seebeck coefficient and affects the ZT value. Therefore, if the holes concentration can be reduced through doping, its thermoelectric performance can be improved. It is known from other studies that the doping of Sb and Bi in GeTe will affect electrons and phonons and improve the thermoelectricity value. Therefore, in this experiment, we will focus on discussing the influence of impurities on phonon scattering and the reduction of thermal conductivity after sample doping. We used cold neutron triple-axis spectrometer SIKA in Ansto for inelastic neutron scattering measurement. First, we measured the elastic neutron scattering pattern in the temperature range of 300 K to 710 K. It was found that the sample changed from R3m to Fm3?m phase in the temperature range of 625 K to 710 K, where two structural phases coexist. In addition, we draw the phonon dispersion diagram of Ge0.86Sb0.08Bi0.06Te in the temperature range of 300 K to 680 K, and obtain the Brillouin zone boundary lattice harmonic energy Eh, electron-phonon interaction energy Ee-p and anharmonic energy Ea. It is found that in this temperature range lattice anharmonicity and very strong electron-phonon interaction occur. In addition, due to the strong electron-phonon scattering, the phonon energy is softened. The properties of the phonon group velocity, phonon lifetime, and propagation length are obtained by fitting. It is known that the sample has a shorter phonon lifetime and phonon propagation length after mixing, and the group velocity will change to a negative value at a large q value. These factors limit the heat transfer and reduce the lattice thermal conductivity of Ge0.86Sb0.08Bi0.06Te, thereby increasing the ZT value of the sample.
顯示於類別:	[物理研究所] 博碩士論文

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