Crossover from Boltzmann to Wigner thermal transport in thermoelectric skutterudites

Skutterudites are crystals with a cagelike structure that can be augmented with filler atoms (“rattlers”), usually leading to a reduction in thermal conductivity that can be exploited for thermoelectric applications. Here, we leverage the recently introduced Wigner formulation of thermal transport to elucidate the microscopic physics underlying heat conduction in skutterudites, showing that filler atoms can drive a crossover from the Boltzmann to the Wigner regimes of thermal transport, i.e., from particlelike conduction to wavelike tunneling. At temperatures where the thermoelectric efficiency of skutterudites is largest, wavelike tunneling can become comparable to particlelike propagation. We define a Boltzmann deviation descriptor able to differentiate the two regimes and relate the competition between the two mechanisms to the materials' chemistry, providing a design strategy to select rattlers and identify optimal compositions for thermoelectric applications.

斯库特鲁德矿是一种具有类似笼状结构的晶体，其结构可通过填充原子（“摇动者”）进行增强，这通常会导致热导率的降低，该特性可被用于热电应用。在本研究中，我们利用最近引入的维格纳热传输公式，阐明了斯库特鲁德矿中热传导的微观物理机制，表明填充原子可以驱动热传输从玻尔兹曼到维格纳区域的转变，即从粒子传导到波动隧穿。在斯库特鲁德矿热电效率最大的温度下，波动隧穿可以与粒子传播相当。我们定义了一个玻尔兹曼偏差描述符，能够区分这两种区域，并将两种机制之间的竞争与材料的化学性质相关联，提供了一种选择填充原子和确定热电应用最佳组成的策略。