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Title: Glass‐Like Through‐Plane Thermal Conductivity Induced by Oxygen Vacancies in Nanoscale Epitaxial La 0.5 Sr 0.5 CoO 3− δ
Abstract

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 LaAlO3and SrTiO3substrates. 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‐temperatureΛLSCOof LSCO on both substrates (1.7 W m−1K−1) are nearly a factor of four lower than that of bulk single‐crystal LSCO (6.2 W m−1K−1). Remarkably, this approaches the lower limit of amorphous oxides (e.g., 1.3 W m−1K−1for 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 measuredΛLSCOis 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 toΛLSCOalong the through‐plane direction for these ultrathin LSCO films on insulating substrates.

 
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NSF-PAR ID:
10046286
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Advanced Functional Materials
Volume:
27
Issue:
47
ISSN:
1616-301X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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