Levin Emily E, Long Francesca, Douglas Jason E, Buffon Malinda L C, Lamontagne Leo K, Pollock Tresa M, Seshadri Ram
Materials Department, University of California, Santa Barbara, CA 93106, USA.
Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA.
Materials (Basel). 2018 May 28;11(6):903. doi: 10.3390/ma11060903.
Thermoelectric devices, which allow direct conversion of heat into electrical energy, require materials with improved figures of merit ( z T ) in order to ensure widespread adoption. Several techniques have been proposed to increase the z T of known thermoelectric materials through the reduction of thermal conductivity, including heavy atom substitution, grain size reduction and inclusion of a semicoherent second phase. The goal in these approaches is to reduce thermal conductivity through phonon scattering without modifying the electronic properties. In this work, we demonstrate that Ni interstitials in the half-Heusler thermoelectric TiNiSn can be created and controlled in order to improve physical properties. Ni interstitials in TiNi 1.1 Sn are not thermodynamically stable and, instead, are kinetically trapped using appropriate heat treatments. The Ni interstitials, which act as point defect phonon scattering centers and modify the electronic states near the Fermi level, result in reduced thermal conductivity and enhance the Seebeck coefficient. The best materials tested here, created from controlled heat treatments of TiNi 1.1 Sn samples, display z T = 0.26 at 300 K, the largest value reported for compounds in the Ti⁻Ni⁻Sn family.
热电装置可将热能直接转化为电能，为确保其广泛应用，需要具备更高优值（zT）的材料。人们已提出多种技术，通过降低热导率来提高已知热电材料的zT，包括重原子取代、减小晶粒尺寸以及引入半共格第二相。这些方法的目标是通过声子散射降低热导率，同时不改变电子性质。在本研究中，我们证明了可以在半赫斯勒热电材料TiNiSn中生成并控制镍间隙原子，以改善其物理性能。TiNi1.1Sn中的镍间隙原子在热力学上并不稳定，而是通过适当的热处理在动力学上被捕获。镍间隙原子作为点缺陷声子散射中心，改变了费米能级附近的电子态，导致热导率降低，并提高了塞贝克系数。通过对TiNi1.1Sn样品进行控制热处理制备的最佳材料，在300 K时zT = 0.26，这是Ti-Ni-Sn族化合物所报道的最大值。
