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Origin of Phonon Glass-Electron Crystal Behavior in Thermoelectric Layered Cobaltate

机译：热电层状钴中声子玻璃-电子晶体行为的起源

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摘要

Measurement of local disorder and lattice vibrations is of great importance for understanding the mechanisms whereby thermoelectric materials efficiently convert heat to electricity. Attaining high thermoelectric power requires minimizing thermal conductivity while keeping electric conductivity high. This situation is achievable by enhancing phonon scattering through specific structural disorder (phonon glass) that also retains sufficient electron mobility (electron crystal). It is demonstrated that the quantitative acquisition of multiple annular-dark-field images via scanning transmission electron microscopy at different scattering-angles simultaneously allows not only the separation but also the accurate determination of static and thermal atomic displacements in crystals. Applying the unique method to the layered thermoelectric material (Ca_2CoO_3)_(0.62)CoO_2 discloses the presence of large incommensurate displacive modulation and enhanced local vibration of atoms, largely confined within its Ca_2CoO_3 sublayers. Relating the refined disorder to ab initio calculations of scattering rates is a tremendeous challenge. Based on an approximate calculation of scattering rates, it is suggested that this well-defined deterministic disorder engenders static displacement-induced scattering and vibrational-induced resonance scattering of phonons as the origin of the phonon glass. Concurrently, the crystalline CoO_2 sublayers provide pathways for highly conducting electrons and large thermal voltages.
机译：局部无序和晶格振动的测量对于理解热电材料有效地将热量转化为电能的机理非常重要。为了获得高的热电功率，需要在保持高电导率的同时使热导率最小化。这种情况可以通过增强声子通过特定结构无序（声子玻璃）的散射来实现，该结构无序也保留了足够的电子迁移率（电子晶体）。结果表明，通过扫描透射电子显微镜以不同的散射角对多个环形暗场图像进行定量采集，不仅可以实现分离，而且可以准确测定晶体中的静态和热原子位移。将独特的方法应用于层状热电材料（Ca_2CoO_3）_（0.62）CoO_2揭示了存在很大的不相称的位移调制和增强的原子局部振动，这些现象主要局限在其Ca_2CoO_3子层内。将精确的障碍与散射速率的从头算起联系起来是一个巨大的挑战。基于散射率的近似计算，建议这种定义明确的确定性混乱会导致声子的静态位移诱发的声子散射和振动诱发的声子共振散射作为声子玻璃的起源。同时，结晶的CoO_2子层为高传导电子和大热电压提供了路径。

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  • 来源
    《Advanced Functional Materials》 |2013年第46期|5728-5736|共9页
  • 作者

    Lijun Wu; Qingping Meng; Christian Jooss; Jin-Cheng Zheng; H. Inada; Dong Su; Qiang Li; Yimei Zhu;

  • 作者单位

    Brookhaven National Laboratory Upton, NY 11973, USA;

    Brookhaven National Laboratory Upton, NY 11973, USA;

    University of Goettingen 37077 Goettingen, Germany;

    Department of Physics Xiamen University Xiamen 361005, China;

    Hitachi High Technology Ibaraki 312-0032, Japan;

    Brookhaven National Laboratory Upton, NY 11973, USA;

    Brookhaven National Laboratory Upton, NY 11973, USA;

    Brookhaven National Laboratory Upton, NY 11973, USA;

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