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Atomic Scale Control of Thermal Conductivity in LaMnO3/SrMnO3 Superlattices
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DOI：10.1002/aelm.70526.png)
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Abstract
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We report atomic scale structure and phonon thermal transport in (LaMnO3)m/(SrMnO3)n/SrTiO3(100) superlattices (LMO/SMO SLs) with the thickness of individual layers m, n = 1 − 10 u.c. and the thickness ratio m/n = 1, 2. Optical transient thermal reflectivity measurements reveal pronounced differences in the thermal conductivity between SLs with m/n = 1 and SLs with m/n = 2. State-of-the art electron microscopy techniques and ab initio density functional calculations enable us to assign the origin of this difference to the differences in the oxygen octahedral rotation (OOR) angle φOOR within the LMO layers in these SLs. Namely, LMO and SMO layers within the (m/n = 1) SLs possess the same φOOR = 180°, which is characteristic of a cubic structure. In contrast, the m/n = 2 SLs reveal a significantly smaller value φOOR = 165° in LMO and a large φOOR = 180° in SMO. The analysis of experimental data shows that the thermal conductance of the LMO/SMO interfaces in m/n = 2 SLs with OOR misfit is low 0.3 GWm−2K−1, whereas a surprisingly large value of interfacial conductance 1.8 GWm−2K−1 was determined for m/n = 1 SLs without OOR misfit. Moreover, a minimum of thermal conductivity of κmin = 0.3–0.4 Wm−1K−1 has been observed at the interface density 1/(Λ = m+n)∼0.11–0.25 u.c.−1, denoting the crossover between the interface- to volume-dependent thermal conductivity. Our results point out the importance of MnO6 octahedral rotations/tilts as an effective structural control parameter to tune thermal transport and magnetism in LMO/SMO SLs by changing the LMO/SMO thickness ratio.
Keywords:
ab initio DFT calculations
HAADF-STEM
iDPC-STEM
octahedral rotations
perovskite superlattices
thermal transport
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