Glass‐Like Through‐Plane Thermal Conductivity Induced by Oxygen Vacancies in Nanoscale Epitaxial La0.5Sr0.5CoO3−δ |
| |
| Authors: | Xuewang Wu Jeff Walter Tianli Feng Jie Zhu Hong Zheng John F. Mitchell Neven Biškup Maria Varela Xiulin Ruan Chris Leighton Xiaojia Wang |
| |
| Affiliation: | 1. Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN, USA;2. Department of Chemical Engineering and Material Science, University of Minnesota, Minneapolis, MN, USA;3. School of Mechanical Engineering and the Birck Nanotechnology Center, Purdue University, West Lafayette, IN, USA;4. Materials Science Division, Argonne National Laboratory, Argonne, IL, USA;5. Departamento de Fisica de Materiales & Instituto Pluridisciplinar, Universidad Complutense de Madrid, Madrid, Spain |
| |
| Abstract: | Ultrafast time‐domain thermoreflectance (TDTR) is utilized to extract the through‐plane thermal conductivity (Λ LSCO) 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 Λ LSCO 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 Λ LSCO 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 Λ LSCO along the through‐plane direction for these ultrathin LSCO films on insulating substrates. |
| |
| Keywords: | nanoscale epitaxial LSCO oxygen vacancies perovskite thermal conductivity time‐domain thermoreflectance |
|
|
