Terahertz (THz) spectroscopy is used to measure permittivity (100 GHz–2.5 THz) of ZnO and CuO powders with low fill factor pressed into pellets in a polyethylene binder. We show that porosity (air) of such pressed pellets has a large effect on effective pellet permittivity (∼10%) and on the extracted permittivity of the oxide constituent (∼150%). We explore a two-step analysis based on sequential application of different effective medium models, first to account for the air, and subsequently to extract the oxide's dielectric properties. We show that the combination of Vegard's law and the Maxwell-Garnett model is the best combination to account, respectively, for the air and the oxide powders. In this regard, the capacity that this approach has to adapt to each phase's physical characteristics by using multiple EMMs is an advantage. The resulting oxide permittivities are significantly larger than previously reported for such pellets as a consequence of the porosity. We find for the real relative permittivities of CuO and ZnO ∼12.1 and ∼8.9, respectively, in the THz range.

中文翻译：

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聚乙烯颗粒中压制的 ZnO 和 CuO 粉末的太赫兹介电常数：孔隙率的影响

太赫兹 (THz) 光谱用于测量在聚乙烯粘合剂中压成颗粒的具有低填充因子的 ZnO 和 CuO 粉末的介电常数 (100 GHz–2.5 THz)。我们表明，这种压制颗粒的孔隙率（空气）对有效颗粒介电常数（~10%）和氧化物成分的提取介电常数（~150%）有很大影响。我们探索了基于连续应用不同有效介质模型的两步分析，首先考虑空气，然后提取氧化物的介电特性。我们表明，Vegard 定律和 Maxwell-Garnett 模型的组合是分别考虑空气和氧化物粉末的最佳组合。在这方面，这种方法必须通过使用多个 EMM 来适应每个相的物理特性的能力是一个优势。由于孔隙率的原因，由此产生的氧化物介电常数明显大于先前报道的这种颗粒的介电常数。我们发现，在太赫兹范围内，CuO 和 ZnO 的实际相对介电常数分别为 ~12.1 和 ~8.9。