Entropy engineering and interface optimization in materials for highly effective thermoelectric energy conversion

热电材料发电机可以将废热转化为电能，通过减少化石燃料的消耗和二氧化碳的排放，为可持续能源供应做出贡献。然而，热电发电机技术的开发仍然有限，因为效率适中，在材料特定连接技术方面尚未解决的挑战，以及由于目前涉及有毒和稀有元素而对可持续性的担忧。来自AGH-UST（波兰），UDE和DLR（德国）的领先实验室将共同努力解决这些挑战，旨在从银柱石和硅化镁固体溶液中开发高效热电材料，使其符合廉价和环保能源转换器的使用条件。我们提出以下策略：利用熵工程（EE）方法在较低温度下稳定银柱石中有利的高对称性a相，从而合成具有良好电子能带结构的新型银柱石，并增加银柱石和硅化镁基固溶体的掺杂溶解度。2. 纳米级结构多相样品的合成。纳米结构可以通过利用混相间隙（对于硅化镁基固溶体）或通过调整构型熵来控制二次相（银晶石）的分离来实现。由于声子散射的增加和在形成的内部界面上有害载流子的能量过滤，可以预期材料的热电性能的增强。利用开尔文探针力显微镜（Kelvin Probe Force Microscopy）和扫描热显微镜（Scanning Thermal Microscopy）进行热表征，可以直接评估多相复合材料中多重成分依赖掺杂等先进策略的效果，其空间分辨率为10 nm，以前很少应用于热电材料。3. 这些基于原子力显微镜的扫描技术也将用于确定Mg2X和银柱石连接到选定电极材料的电和热接触电阻，因为这些电极是在设备中操作功能材料的先决条件。利用极好的空间分辨率，我们将追踪热的微观来源以及外部界面的电阻，并确定实验杠杆来减少它们。局部测量、微观结构表征和输运模型将用于理解整体热电性能。基于第一性原理的电子能带结构计算将支持材料开发的实验工作。最后，我们将制作硅化镁/银晶石单极偶原型，以便从组装的角度评估这种有前途的材料组合的巨大应用潜力。

Generators from thermoelectric materials can convert waste heat into electricity and contribute to a sustainable energy supply by reducing the consumption of fossil fuels and the emission of CO2. However, the exploitation of thermoelectric generator technology remains limited due to moderate efficiency, unsolved challenges in material-specific joining technologies and concerns on sustainability because of the current involvement of toxic and rare elements. A concerted effort of leading laboratories from AGH-UST (Poland), UDE and DLR (Germany) will address these challenges, aiming at developing highly effective thermoelectric materials from the families of argyrodites and magnesium silicide-based solid solutions, qualifying them for the usage in inexpensive and eco-friendly energy converters. We propose the following strategies: 1. Exploitation of an Entropy Engineering (EE) approach to stabilize the favorable high-symmetry a-phase in argyrodites at lower temperatures, to allow for the synthesis of novel argyrodites with a favorable electronic band structure and to increase the dopant solubility for both argyrodites and magnesium silicide-based solid solutions. 2. Synthesis of multiphase samples with structuring at the nm-scale. Nanostructuring can be achieved by controlled unmixing making use of the miscibility gap (for magnesium silicide based solid solutions) or secondary phases (argyrodites) by adjustment of the configurational entropy. Enhancement of the thermoelectric properties of the materials can be expected due to a combination of increased phonon scattering and an energy filtering of detrimental charge carriers at formed internal interfaces. The effect of advanced strategies like multiple, composition-dependent doping in multiphase composites can be evaluated directly employing Kelvin Probe Force Microscopy for electrical and Scanning Thermal Microscopy for thermal characterization with a spatial resolution of several 10 nm, rarely applied to thermoelectric materials before. 3. These AFM-based scanning techniques will also be employed to determine electrical and thermal contact resistances of Mg2X and argyrodites joined to selected electrode materials as these electrodes are a prerequisite to operate the functional materials in a device. Making use of the superb spatial resolution we’ll trace the microscopic origin of the thermal along with the electrical resistances of external interfaces and identify experimental levers to reduce them. Local measurements, microstructural characterization and transport modelling will be used to understand the integral thermoelectric performance. Experimental efforts in material development will be supported by first-principle based electronic band structure calculations. Finally, a magnesium silicide/argyrodite pn-uni-couple prototype shall be fabricated so that the tremendous application potential of this promising material combination can be evaluated also from an assembly point of view.