Phononic origin of the infrared dielectric properties of RE₂O₃ (RE = Y, Gd, Ho, Lu) compounds

Understanding the phononic origin of the infrared dielectric properties of yttria (Y₂O₃) and other rare-earth sesquioxides (RE₂O₃) is a fundamental task in the search of appropriate RE₂O₃ materials that serve particular infrared optical applications. We herein investigate the infrared dielectric properties of RE₂O₃ (RE = Y, Gd, Ho, Lu) using DFT-based phonon calculations and Lorentz oscillator model. The abundant IR-active optical phonon modes that are available for effective absorption of photons result in high reflectance of RE₂O₃, among which four IR-active modes originated from large distortions of REO₆ octahedra are found to contribute dominantly to the phonon dielectric constants. Particularly, the present calculation method by considering one-phonon absorption process is demonstrated with good reliability in predicting the infrared dielectric parameters of RE₂O₃ at the far-infrared as well as the vicinity of mid-infrared region, and the potential cutoff frequency/wavelength of its applicability is disclosed as characterized by the maximum frequency of IR-active longitudinal phonon modes. The results deepen the understanding on infrared dielectric properties of RE₂O₃, and aid the computational design of materials with appropriate infrared properties.

探讨钇氧化物（Y₂O₃）及其他稀土三氧化二物（RE₂O₃）的红外介电性质之声子起源，是寻找适用于特定红外光学应用的理想RE₂O₃材料的基本任务。本研究采用基于DFT的声子计算和洛伦兹振荡器模型，对RE₂O₃（RE = Y, Gd, Ho, Lu）的红外介电性质进行了研究。丰富的红外活性光学声子模式，能够有效吸收光子，导致RE₂O₃具有较高的反射率。其中，源自REO₆八面体大畸变的四个红外活性模式被发现对声子介电常数有显著贡献。特别是，通过考虑单声子吸收过程，本研究所采用的计算方法在预测远红外及中红外邻近区域RE₂O₃的介电参数方面展现了良好的可靠性，并揭示了其适用性的截止频率/波长的潜在极限，这一极限由红外活性纵波模式的最大频率所表征。这些研究结果加深了对RE₂O₃红外介电性质的理解，并有助于计算设计具有适当红外特性的材料。