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On the origin of vibrational properties of calcium manganate based thermoelectric compounds
Nano Energy ( IF 16.8 ) Pub Date : 2018-03-06 , DOI: 10.1016/j.nanoen.2018.02.054
Andrei Baranovskiy , Ayelet Graff , Janina Klose , Joachim Mayer , Yaron Amouyal

Vibrational properties of CaO(CaMnO3)m (m = 1, 2, 3, and ∞) thermoelectric (TE) oxides for high-temperature energy conversion applications are studied both experimentally and computationally. Density functional theory (DFT) calculations reveal strong scattering events involving dispersive acoustic phonons and non-dispersive optical modes in the frequency range of 3–5 THz. We demonstrate that the low frequency parts of the phonon spectra are strongly dominated by Ca-sublattice oscillations for all compounds of the CaO(CaMnO3)m (m = 1,2,3, ∞) series, which predicts enhanced phonon scattering upon Ca-sublattice site substitution defects. Accordingly, laser flash analysis (LFA) indicates considerable decrease of thermal conductivity (κ) due to La- substitution for Ca, whereas Nb- substitution for Mn-sites does not affect κ noticeably. It is found that thermal conductivity of CaO(CaMnO3)m compounds is governed by phonon scattering on CaO/CaMnO3 boundaries for m = 1, 2, and 3 and by Umklapp processes for m = ∞. Thermal transport in this system is strongly dominated by acoustic phonon modes possessing much larger Grüneisen parameters (γ) compared to optical ones.



中文翻译:

锰酸钙基热电化合物振动特性的起源

通过实验和计算研究了用于高温能量转换应用的CaO(CaMnO 3m(m = 1、2、3和∞)热电(TE)氧化物的振动特性。密度泛函理论(DFT)计算揭示了在3–5 THz频率范围内涉及色散声子和非色散光学模式的强散射事件。我们证明,对于CaO(CaMnO 3m的所有化合物,声子谱的低频部分主要由Ca亚晶格振荡决定(m = 1,2,3,∞)级数,它预测在Ca-亚晶格位点置换缺陷后声子散射会增强。因此,激光闪光分析(LFA)表明,由于La取代Ca,导致热导率(κ)大大降低,而Mn部位的Nb取代则对κ没有明显影响。已经发现,对于m = 1、2和3 ,CaO(CaMnO 3m化合物的导热系数受CaO / CaMnO 3边界上的声子散射影响,对于m =∞则受Umklapp过程控制。该系统中的热传输主要由声子声子模式主导,声子声子模式与光学参数相比具有更大的Grüneisen参数(γ)。

更新日期:2018-03-06
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