The origin of uniaxial negative thermal expansion in layered perovskites
The origin of uniaxial negative thermal expansion in layered perovskites
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DOI：
10.1038/s41524-017-0040-0
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发表时间：
2017-10-16
影响因子：
9.7
通讯作者：
Bristowe, Nicholas C.
中科院分区：
文献类型：
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作者：
Ablitt, Chris;Craddock, Sarah;Bristowe, Nicholas C.
为什么ABO(3)钙钛矿通常不会在很宽的温度范围内表现出负热膨胀（NTE），而同一化学家族的层状钙钛矿却经常表现出负热膨胀？人们普遍认为，有两个关键因素决定了NTE的程度：驱动收缩的软声子模式的存在（具有负Gruneisen参数）；以及各向异性弹性顺应性，使材料易于沿特定轴产生NTE所需的变形。这种热膨胀性能的差异是令人惊讶的，因为ABO(3)和层状钙钛矿通常在其高对称相中具有等量的这些成分。利用第一性原理计算和对称性分析，我们发现在层状钙钛矿中，由于氧八面体的分层和凝聚旋转的共同作用导致的对称性破坏，弹性各向异性显著增强。这种特性是具有一定对称性的层状钙钛矿所特有的，是单轴NTE在大温度范围内持续存在的原因。这一基本见解意味着对称和弹性张量可以用作高通量筛选和指导材料设计的描述符。
Why is it that ABO(3) perovskites generally do not exhibit negative thermal expansion (NTE) over a wide temperature range, whereas layered perovskites of the same chemical family often do? It is generally accepted that there are two key ingredients that determine the extent of NTE: the presence of soft phonon modes that drive contraction (have negative Gruneisen parameters); and anisotropic elastic compliance that predisposes the material to the deformations required for NTE along a specific axis. This difference in thermal expansion properties is surprising since both ABO(3) and layered perovskites often possess these ingredients in equal measure in their high-symmetry phases. Using first principles calculations and symmetry analysis, we show that in layered perovskites there is a significant enhancement of elastic anisotropy due to symmetry breaking that results from the combined effect of layering and condensed rotations of oxygen octahedra. This feature, unique to layered perovskites of certain symmetry, is what allows uniaxial NTE to persist over a large temperature range. This fundamental insight means that symmetry and the elastic tensor can be used as descriptors in high-throughput screening and to direct materials design.