Utilising unit-cell twinning operators to reduce lattice thermal conductivity in modular structures: Structure and thermoelectric properties of Ga2O3(ZnO)9
Utilising unit-cell twinning operators to reduce lattice thermal conductivity in modular structures: Structure and thermoelectric properties of Ga2O3(ZnO)9
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DOI：
10.1016/j.jallcom.2018.05.260
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发表时间：
2018-09
影响因子：
6.2
通讯作者：
Diana T. Alvarez -Ruiz;F. Azough;D. Hernández-Maldonado;D. Kepaptsoglou;Q. Ramasse;S. Day;P. Švec;R. Freer
中科院分区：
文献类型：
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作者：
Diana T. Alvarez -Ruiz;F. Azough;D. Hernández-Maldonado;D. Kepaptsoglou;Q. Ramasse;S. Day;P. Švec;R. Freer
Ga_2O_3（ZnO）_m系列同系化合物已被确定为潜在的热电材料，但由于低致密化，性能往往受到限制。利用B_2O_3作为液相烧结助剂，合成了高致密度、高质量的Ga_2O_3（ZnO）_9陶瓷样品。用高分辨X射线衍射和原子分辨STEM-HAADF、EDS和EELS测量方法，确定了Ga_2O_3（ZnO）_9的原子结构和局部化学组成。X-射线衍射分析表明，该化合物为C-斜方晶系。原子分辨的HAADF-STEM图像明确地显示了平行于b轴的纳米尺寸的楔形孪晶边界的存在。这些纳米尺度的结构特征进行了化学研究，首次揭示了Zn和Ga的确切分布，发现Ga离子占据孪晶界和反转晶界的交界处。HAADF-EDS分析表明，煅烧步骤对晶体结构均匀性具有显著影响。通过使用烧结助剂和优化工艺参数，陶瓷的热导率为1.5-2.2 W/m.K（温度范围为300-900 K），功率因数为40-90 μW/K. m 2，在900 K时ZT为0.06。这项工作显示了一条路线，利用纳米界面功能，以降低热导率，从而提高复杂的热电材料的热电品质因数。
The Ga2O3(ZnO)mfamily of homologous compounds have been identified as potential thermoelectric materials, but properties are often limited due to low densification. By use of B2O3as an effective liquid phase sintering aid, high density, high quality ceramic samples of Ga2O3(ZnO)9have been synthesised. The atomic structure and local chemical composition of Ga2O3(ZnO)9have been determined by means of high resolution X-ray diffraction and atomic resolution STEM-HAADF, EDS and EELS measurements. X-ray analysis showed that the compound crystalizes in theCmcmorthorhombic symmetry. Atomically resolved HAADF-STEM images unambiguously showed the presence of nano-sized, wedge-shaped twin boundaries, parallel to the b-axis. These nano-scale structural features were chemically investigated, for the first time, revealing the exact distributions of Zn and Ga; it was found that Ga ions occupy sites at the junction of twin boundaries and inversion boundaries. HAADF-EDS analysis showed that the calcination step has a significant impact on crystal structure homogeneity. By use of a sintering aid and optimization of processing parameters the ceramics achieved a low thermal conductivity of 1.5–2.2 W/m.K (for the temperature range 300–900 K), a power factor of 40–90 μW/K.m2, leading to a ZT of 0.06 at 900 K. The work shows a route to exploit nanoscale interface features to reduce the thermal conductivity and thereby enhance the thermoelectric figure of merit in complex thermoelectric materials.