Liu Xiaodong, Kepaptsoglou Demie, Gao Zhaohe, Thomas Andrew, Maji Krishnendu, Guilmeau Emmanuel, Azough Feridoon, Ramasse Quentin M, Freer Robert
Department of Materials, University of Manchester, Manchester M13 9PL, United Kingdom.
SuperSTEM Laboratory, STFC Daresbury Campus, Daresbury, Warrington WA4 4AD, United Kingdom.
ACS Appl Mater Interfaces. 2021 Dec 8;13(48):57326-57340. doi: 10.1021/acsami.1c18236. Epub 2021 Nov 29.
Donor-doped TiO ceramics are promising high-temperature oxide thermoelectrics. Highly dense (1 - )TiO-NbO (0.005 ≤ ≤ 0.06) ceramics were prepared by a single-step, mixed-oxide route under reducing conditions. The microstructures contained polygonal-shaped grains with uniform grain size distributions. Subgrain structures were formed in samples with low Nb contents by the interlacing of rutile and higher-order Magnéli phases, reflecting the high density of shear planes and oxygen vacancies. Samples prepared with a higher Nb content showed no subgrain structures but high densities of planar defects and lower concentrations of oxygen vacancies. Through optimizing the concentration of point defects and line defects, the carrier concentration and electrical conductivity were enhanced, yielding a much improved power factor of 5.3 × 10 W m K at 823 K; lattice thermal conductivity was significantly reduced by enhanced phonon scattering. A low, temperature-stable thermal conductivity of 2.6 W m K was achieved, leading to a ZT value of 0.17 at 873 K for compositions with = 0.06, the highest ZT value reported for single Nb-doped TiO ceramics without the use of spark plasma sintering (SPS). We demonstrate the control of the thermoelectric properties of Nb-doped TiO ceramics through the development of balanced defect structures, which could guide the development of future oxide thermoelectric materials.
施主掺杂的TiO陶瓷是很有前景的高温氧化物热电材料。在还原条件下，通过单步混合氧化物路线制备了高致密性的(1 - )TiO-NbO(0.005 ≤ ≤ 0.06)陶瓷。其微观结构包含晶粒尺寸分布均匀的多边形晶粒。在低Nb含量的样品中，通过金红石相和高阶马涅利相的交错形成了亚晶粒结构，这反映了高密度的剪切面和氧空位。高Nb含量制备的样品没有亚晶粒结构，但有高密度的平面缺陷和较低浓度的氧空位。通过优化点缺陷和线缺陷的浓度，载流子浓度和电导率得到提高，在823 K时功率因数大幅提高至5.3×10 W m K；通过增强声子散射，晶格热导率显著降低。实现了2.6 W m K的低温稳定热导率，对于 = 0.06的成分，在873 K时ZT值达到0.17，这是未使用火花等离子烧结(SPS)的单一Nb掺杂TiO陶瓷报道的最高ZT值。我们通过开发平衡的缺陷结构证明了对Nb掺杂TiO陶瓷热电性能的控制，这可为未来氧化物热电材料的开发提供指导。
