One-Order Decrease of Thermal Conductivity in Nanostructured ZrTe5 and HfTe5 Crystals

作者：Yanyan Zhang, Di Chen, Yang‐Yang Lv, Songtao Dong, Jian Zhou, Shu‐Hua Yao, Y. B. Chen, Y. B. Chen, Ming‐Hui Lu, Yan‐Feng Chen, Yan‐Feng Chen · 发表于：Crystal Growth & Design · 年份：2019 · DOI：10.1021/acs.cgd.9b01108 · 被引用次数：7 · 研究领域：Advanced Thermoelectric Materials and Devices、Thermal properties of materials、Thermal Radiation and Cooling Technologies

Thermoelectric materials have been hotly explored for potential applications of environmentally friendly electrical generators and freon-free refrigerators. ZrTe 5 and HfTe 5 crystals have a superior power factor but relative large thermal conductivity. To decrease their thermal conductivity, we here grew ZrTe 5 and HfTe 5 with nanostructures by optimizing the growth parameters, with a growth mechanism that follows nucleation-then-nuclei-coalescence. Microstructure characterizations verify that nanostructured ZrTe 5 and HfTe 5 crystals have not only a layered microstructure but also nanostripe morphology. For comparison, we had grown compact ZrTe 5 crystals by the flux method that mainly have a layered microstructure. Remarkably, the maximum thermal conductivity of nanostructured ZrTe 5 and HfTe 5 crystals can be suppressed to as small as 0.45 W m –1 K –1, one order lower than the theoretical value and three times smaller than that of compact ZrTe 5 and HfTe 5 . Theoretical cumulative thermal conductivities, to simulate the effect of boundary scattering in nanostructured ZrTe 5, roughly agree with experimental results. Phenomenological thermal conductivity analysis verifies that the phonon mean-free paths of nanostructured ZrTe 5 and HfTe 5 reach the thickness of a monolayer (Ioffe–Regel criterion of phonon transport). Raman spectroscopy substantiates that the quasi-particle lifetime of optical phonons in nanostructured ZrTe 5 and HfTe 5 crystals is nearly four times larger t...