| Autor: |
Wu, Xuewang, Walter, Jeff, Feng, Tianli, Zhu, Jie, Zheng, Hong, Mitchell, John F., Biškup, Neven, Varela, Maria, Ruan, Xiulin, Leighton, Chris, Wang, Xiaojia |
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| Zdroj: |
Advanced Functional Materials; Dec2017, Vol. 27 Issue 47, pn/a-N.PAG, 11p |
| Abstrakt: |
Ultrafast time-domain thermoreflectance (TDTR) is utilized to extract the through-plane thermal conductivity ( ΛLSCO) of epitaxial La0.5Sr0.5CoO3− δ (LSCO) of varying thickness (<20 nm) on LaAlO3 and SrTiO3 substrates. These LSCO films possess ordered oxygen vacancies as the primary means of lattice mismatch accommodation with the substrate, which induces compressive/tensile strain and thus controls the orientation of the oxygen vacancy ordering (OVO). TDTR results demonstrate that the room-temperature ΛLSCO of LSCO on both substrates (1.7 W m−1 K−1) are nearly a factor of four lower than that of bulk single-crystal LSCO (6.2 W m−1 K−1). Remarkably, this approaches the lower limit of amorphous oxides (e.g., 1.3 W m−1 K−1 for glass), with no dependence on the OVO orientation. Through theoretical simulations, origins of the glass-like thermal conductivity of LSCO are revealed as a combined effect resulting from oxygen vacancies (the dominant factor), Sr substitution, size effects, and the weak electron/phonon coupling within the LSCO film. The absence of OVO dependence in the measured ΛLSCO is rationalized by two main effects: (1) the nearly isotropic phononic thermal conductivity resulting from the imperfect OVO planes when δ is small; (2) the missing electronic contribution to ΛLSCO along the through-plane direction for these ultrathin LSCO films on insulating substrates. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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