The structure and thermoelectric properties of tungsten bronze Ba6Ti2Nb8O30
The structure and thermoelectric properties of tungsten bronze Ba6Ti2Nb8O30
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DOI：
10.1063/1.5119962
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发表时间：
2019-09-28
影响因子：
3.2
通讯作者：
Freer, Robert
中科院分区：
文献类型：
--
作者：
Jiang, Dongting;Ekren, Dursun;Freer, Robert
钨青铜(Tb)结构材料因其复杂的晶体结构而成为热电材料的研究热点。本文以放电等离子烧结(SPS)法制备了具有四方钨青铜(TB)结构的新型热电陶瓷Ba6Ti2Nb8O30(BTN)。MnO的加入使BTN陶瓷在1580K的低温空气中和SPS烧结条件下获得了高密度的陶瓷。所有样品在烧结后均在还原气氛中进行退火热处理。X射线衍射分析表明，Ba6Ti2Nb8O30具有四方对称(P4bm空间群)晶型。高角环形暗场-电子能量损失谱分析证实了所提出的晶体结构，并提供了晶格中准确的元素分布，表明2b晶格中的钛浓度高于8d晶格中的钛浓度。X射线光电子能谱显示在207.7 eV处存在两个自旋-轨道双峰，证实了Nb4+离子的存在。通过使用助烧剂和优化工艺参数，BTN陶瓷在873K时的功率因数达到280mW/mK-2，在300-873K时的热导率为1.7-1.65W/mK，表现为声子-玻璃型导热行为，在873K时的热电优值(ZT)为0.14，可与许多Tb热电材料的结果相媲美。然而，BTN具有处理容易得多的优势。
Tungsten bronze (TB) structured materials have attracted attention as possible thermoelectrics because of their complex crystal structure. In this work, a new thermoelectric ceramic with a tetragonal tungsten bronze (TB) structure, Ba6Ti2Nb8O30 (BTN), was prepared by the conventional mixed oxide route with some samples processed by Spark Plasma Sintering (SPS). The addition of MnO enabled the fabrication of high density BTN ceramics at a low sintering temperature of 1580 K in air and by SPS. All samples were annealed in a reducing atmosphere after sintering. X-ray diffraction showed that Ba6Ti2Nb8O30 crystallizes with tetragonal symmetry (P4bm space group). High angle annular dark field-electron energy loss spectroscopy analysis confirmed the proposed crystal structure and provided exact elemental distributions in the lattice, showing higher concentrations of Ti in the 2b lattice sites compared to the 8d lattice sites. XPS showed the presence of two spin-orbit double peaks at 207.7 eV in the reduced BTN samples, confirming the presence of Nb4+ ions. By the use of a sintering aid and optimization of the processing parameters, the ceramics achieved a high power factor of 280 mu W/m K-2 at 873 K. The BTN ceramics showed phonon-glass-type thermal conduction behavior with a low thermal conductivity of 1.7-1.65 W/m K at 300-873 K. A thermoelectric figure of merit (ZT) of 0.14 was achieved at 873 K. This ZT value is comparable with results for many TB thermoelectrics. However, BTN has the advantage of much easier processing.