高温金属钙钛矿氧化物的输运性质调控

Nowadays, due to the global environmental and energy crisis, it is of great practical significance and value to develop high-performance perovskite oxides (PO) thermoelectric materials to make use of industrial waste heat and natural thermal energy. Although many efforts have been devoted to the improvement of thermoelectric performance of the PO, the figure of merit ZT is still not ideally high enough. This is mainly owing to the fact that the transport mechanism of the PO is not clear and the inherent relationship of electronic structures, transport properties, vibration modes, and atomic distortions has not been well understood. Our previous works indicate the symmetry-adapted vibration modes and atomic distortions could greatly affect the transport properties (i.e., Seebeck coefficient) of the conducting PO. Hence, we expect it also works in non-conducting PO, but the transport mechanism is not known yet. Taking advantage of first-principles calculations, density functional perturbation theory and supercell methods, Boltzmann transport theory, and symmetry-adapted mode analysis, this project intends to explore the role of different vibration modes and atomic distortions on the electronic structures of non-conducting PO and to establish a clear physico-chemical picture and understanding on the manipulation of their transport properties. Furthermore, as a result of this project, new optimization strategies and design guidelines for high-performance thermoelectric PO will be proposed, which will provide a theoretical basis for further improvement of the thermoelectric performance and benefit to the development of PO-related thermoelectric materials and devices.

研发高性能高温金属钙钛矿氧化物（PO）热电材料对于利用工业余热和自然界温差来发电具有重要的意义。然而，PO的热电优值较低。尽管人们采用多种方法来提高PO的热电性能，但效果有限，究其主要原因是PO电子及原子层次的输运性质调控机制不清晰，且其电子结构和输运性质与振动模及原子畸变的内在关联也不明确。我们的前期工作表明，对称自适应振动模及原子畸变会影响导电PO的塞贝克系数等性质。因此，我们预测振动模和原子畸变也可以调控非导电PO的输运性质，但目前尚无相关报道且其机制不清楚。本项目拟针对非导电PO的输运性质调控机制等科学问题，采用第一性原理计算、密度泛函微扰理论和超胞方法、玻尔兹曼输运理论和对称自适应振动模分析等方法和技术，探索振动模和原子畸变对PO电子结构的作用规律，建立其输运性质调控的物理化学模型，并提出新的性能改进措施和材料设计准则，为优化其热电性能和研发相关高性能PO热电材料提供理论基础。

在现实工业生产活动中，有20%到50%的能源以废气、冷却水或表面散热的形式被释放到自然界中而浪费。因此，研制可用于高温下将热能转换为电能的热电材料具有很高的经济价值和现实意义。该项目围绕高温金属钙钛矿氧化物等潜在热电材料的电子及原子层次热电调控机制及其电子结构、输运性质与振动模和原子畸变的内在关联等科学问题和难点，通过第一性原理计算、密度泛函微扰理论/超胞方法、半经典玻尔兹曼输运理论和对称自适应振动模分析等方法和技术，开展振动模/原子畸变/载流子浓度等关键要素对材料热电输运性质的调控研究和新型热电材料设计，取得的主要结果包括：(i)以典型的CaMnO3钙钛矿为例，通过理论预测获得了与实验测量值接近的塞贝克系数等热电参量；进而发现载流子掺杂会降低其塞贝克系数，但提升电导率，从而提高材料的总体热电性质；在电子载流子浓度达到1E21/cm3时，其功率因数达到峰值；倾斜振动模式对CaMnO3的热电性能调控具有一定规律性；其中，纯氧旋转倾斜模式（R5-和M2+）对CaMnO3热电性能影响最大，反极性阳离子运动（X5-和R4-）的影响次之，而姜泰勒效应（M3+）的影响最小；通过调节CaMnO3内的振幅，移除纯氧旋转模式（0R5-+0M2+）或者施加5倍增强幅度X5-型阳离子反极性运动模式的功率因子比原始基态结构的提升了约1.8倍；不过，对CaMnO3的倾斜模式进行调节后，再进行载流子调控，难以使其功率因子超越掺杂的CaMnO3。（ii）基于物理化学模型、材料设计准则及已有知识和材料大数据，通过高通量计算和筛选获得了若干具有优异综合性能新型金属氧化物热电材料；其中，MgTa2O6和SrTiO3钙钛矿的热电性能最佳，其最高ZT值分别达到1.06和0.33，故可作为潜在候选材料用于未来的高温热防护涂层及热电转化器件中。