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arXiv 1907.02008cond-mat.mtrl-sci
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BaZrO3单晶的晶格动力学和拉曼光谱

Lattice dynamics and Raman spectrum of BaZrO3 single crystals

Constance Toulouse, Danila Amoroso, Cong Xin, Philippe Veber, Monica Ciomaga Hatnean, Geetha Balakrishnan, Mario Maglione, Philippe Ghosez, Jens Kreisel, Mael Guennou

摘要:

BaZrO 3是一种钙钛矿,在所有温度下都保持简单的立方相,因此没有对称性允许的一阶拉曼活性声子模式。然而,它表现出强烈的拉曼光谱,具有清晰和明确的特征。本文报道了BaZrO_3单晶在宽温度范围(4- 1200 ~K)内的拉曼光谱的演化,并在详细的晶格动力学第一性原理计算的支持下讨论了其起源。声子计算进行不仅为立方相的BaZrO 3,但也为低对称相的八面体倾斜,已被怀疑存在于纳米尺度。我们发现,拉曼光谱显示这些纳米畴没有直接的证据,而是可以解释为经典的二阶拉曼散射。我们提供了一个分配的主要功能声子模式的组合。特别是,我们表明,频谱的高频范围占主导地位的泛音,并显示图像的声子密度的状态对应的氧八面体的拉伸模式。

英文摘要:

BaZrO3 is a perovskite that remains in the simple cubic phase at all temperatures, hence with no first-order Raman-active phonon mode allowed by symmetry. Yet, it exhibits an intense Raman spectrum with sharp and well-defined features. Here, we report the evolution of the Raman spectrum of BaZrO3 single crystals in a broad temperature range (4--1200~K) and discuss its origin with the support of detailed first-principle calculations of the lattice dynamics. Phonon calculations are performed not only for the cubic phase of BaZrO3, but also for the low-symmetry phases with octahedra tilts that have been suspected to exist at the nanoscale. We show that the Raman spectrum shows no direct evidence for these nanodomains, but can instead be explained by classical second-order Raman scattering. We provide an assignment of the dominant features to phonon modes combinations. In particular, we show that the high frequency range of the spectrum is dominated by overtones and shows an image of the phonon density of states corresponding to the stretching modes of the oxygen octahedra.

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