Dielectric properties of micaceous clays determined by terahertz time-domain spectroscopy

Abstract

Micaceous layered clay minerals, as utilized in many electro-technical applications, were studied by terahertz time-domain spectroscopy (THz-TDS). The dielectric behavior of clay samples was investigated in a far-infrared region of 0.8 and 6.0 THz corresponding to ∼27 to 200 cm–1, respectively. The samples were also characterized by X-ray diffraction and Fourier transform infrared spectroscopy, and chemical analysis by energy dispersive X-ray spectroscopy. Muscovite with dehydrated K+ interlayer cations was compared with vermiculite having hydrated Mg2+ interlayer cations. The frequency dependence of complex index of refraction varied between 2.43 and 2.48 for muscovite and from 2.23 to 2.08 for vermiculite. The frequency dependence of the power absorption coefficient revealed clear absorption bands for muscovite at 1.95 THz (65 cm−1) and 4.60 THz (153.4 cm−1), and asymmetric band at 2.5 THz (83.4 cm−1) for vermiculite. The band positions were compared with far infrared Fourier transform spectroscopic results achieved by conventional techniques. The differences found were attributed to variations in chemical composition and the stacking order of the micaceous clays used.