School of Materials, University of Manchester , Manchester M13 9PL, U.K.
Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, U.K.
ACS Appl Mater Interfaces. 2017 Dec 6;9(48):41988-42000. doi: 10.1021/acsami.7b14231. Epub 2017 Nov 27.
To help understand the factors controlling the performance of one of the most promising n-type oxide thermoelectric SrTiO, we need to explore structural control at the atomic level. In SrLaTiO ceramics (0.0 ≤ x ≤ 0.9), we determined that the thermal conductivity can be reduced and controlled through an interplay of La-substitution and A-site vacancies and the formation of a layered structure. The decrease in thermal conductivity with La and A-site vacancy substitution dominates the trend in the overall thermoelectric response. The maximum dimensionless figure of merit is 0.27 at 1070 K for composition x = 0.50 where half of the A-sites are occupied with La and vacancies. Atomic resolution Z-contrast imaging and atomic scale chemical analysis show that as the La content increases, A-site vacancies initially distribute randomly (x < 0.3), then cluster (x ≈ 0.5), and finally form layers (x = 0.9). The layering is accompanied by a structural phase transformation from cubic to orthorhombic and the formation of 90° rotational twins and antiphase boundaries, leading to the formation of localized supercells. The distribution of La and A-site vacancies contributes to a nonuniform distribution of atomic scale features. This combination induces temperature stable behavior in the material and reduces thermal conductivity, an important route to enhancement of the thermoelectric performance. A computational study confirmed that the thermal conductivity of SrTiO is lowered by the introduction of La and A-site vacancies as shown by the experiments. The modeling supports that a critical mass of A-site vacancies is needed to reduce thermal conductivity and that the arrangement of La, Sr, and A-site vacancies has a significant impact on thermal conductivity only at high La concentration.
为了帮助理解控制最有前途的 n 型氧化物 SrTiO 性能的因素，我们需要在原子水平上探索结构控制。在 SrLaTiO 陶瓷（0.0≤x≤0.9）中，我们确定热导率可以通过 La 取代和 A 位空位的相互作用以及层状结构的形成来降低和控制。随着 La 和 A 位空位取代的增加，热导率的降低主导了整体热电响应的趋势。在组成 x=0.50 时，最大无量纲品质因数为 0.27，此时 A 位有一半被 La 和空位占据。原子分辨率 Z 衬度成像和原子尺度化学分析表明，随着 La 含量的增加，A 位空位最初随机分布（x<0.3），然后聚集（x≈0.5），最后形成层（x=0.9）。分层伴随着从立方到正交的结构相变以及 90°旋转孪晶和反相畴界的形成，导致局域超晶格的形成。La 和 A 位空位的分布导致原子尺度特征的不均匀分布。这种组合导致材料的温度稳定行为，并降低热导率，这是提高热电性能的重要途径。计算研究证实，SrTiO 的热导率通过引入 La 和 A 位空位而降低，这与实验结果一致。该模型支持，引入 A 位空位以降低热导率需要达到一个临界质量，而 La、Sr 和 A 位空位的排列仅在 La 浓度较高时对热导率有显著影响。
