Ultrafast time‐domain thermoreflectance (TDTR) is utilized to extract the through‐plane thermal conductivity (Λ_LSCO) of epitaxial La_0.5Sr_0.5CoO_3−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.

中文翻译：

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氧空位在纳米级外延La0.5Sr0.5CoO3-δ中诱导的类似玻璃的平面热导率

超快时域热反射（TDTR）被用来提取穿过平面的导热率（Λ _LSCO外延的La）_0.5锶_0.5 CoO的_{3- δ}上LaAlO中变化的厚度（<20纳米）的（LSCO）₃和的SrTiO _3个基片。这些LSCO薄膜具有有序的氧空位，作为与基板晶格失配的主要手段，这会引起压缩/拉伸应变，从而控制氧空位有序（OVO）的方向。TDTR结果表明，室温Λ _LSCO在两个基底上的LSCO（1.7脉冲W M ^-1 ķ ^-1）比单晶LSCO（6.2 W m ^-1 K ^-1）低近四倍。显着地，这接近于无定形氧化物的下限（例如，对于玻璃为1.3 W m ^-1 K ^-1），而与OVO取向无关。通过理论模拟，发现了LSCO的玻璃状热导率的起源是由氧空位（主导因素），Sr取代，尺寸效应以及LSCO膜内弱的电子/声子耦合引起的综合效应。在测得的不存在OVO依赖Λ _LSCO它的两个主要影响是合理的：（1）当δ小时，由不完善的OVO平面产生的几乎各向同性的声子热导率；（2）丢失的电子贡献Λ _LSCO沿着上绝缘衬底这些超薄LSCO膜穿过平面方向。