Temperature dependent terahertz spectroscopy study of rare earth modified smectites: Probing the structural responses

• Published in: Applied clay science Vol. 255; p. 107406
• Main Authors: Janek, Marián, Čičkan, Michal, Klement, Robert, Matejdes, Marián, Furka, Daniel, Furka, Samuel, Bača, Ľuboš, Naftaly, Mira
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2024
• Subjects: Cation exchange; Dielectric properties; Heating induced transformation; Rare earth elements; Smectites; Terahertz time-domain spectroscopy; Cation exchange; Heating induced transformation; Rare earth elements; Smectites; Terahertz time-domain spectroscopy; Dielectric properties
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2024.107406

Selected layered clay minerals of smectite group with different chemical composition (e.g. synthetic hectorite, synthetic smectite and natural smectite) were modified by rare earth cations such as Er3+ and a stochiometric mixture of Er3+/Yb3+. Raw and modified smectites were systematically heated up to temperatures ensuring their dehydration (400 °C), dehydroxylation (800 °C) and formation of new high temperature phases (1200 °C). The products of heating were investigated by terahertz-time domain spectroscopy to follow changes of their dielectric properties in the far-infrared region. The frequency-dependent refractive index of raw and modified clays was determined in the range of 0.2–3.8 THz (6.6–126.5 cm−1). The heating at 800 °C and above resulted in increase frequency dependent index of refraction and decrease absorption coefficient in comparison to the raw clays. The ion-exchanged smectites by rare earth cations further decreased the absorption coefficient of the samples heated at 1200 °C. Raw natural smectite sample revealed a low frequency band at 0.86 THz, already reported in the literature, which shifted to 0.67 THz after sample modification by rare earth cations. Heating of modified JP to 1200 °C resolved a new absorption band at ∼3.40 THz in the ceramic phase produced from raw natural smectite. •Cation exchange reaction was used for modification of clays by selected rare earth elements.•Effect of sample heating up to 400, 800 and 1200 °C was studied.•Terahertz time domain spectroscopy was used to study the refractive index dispersion.•The frequency dependence of absorption in THz region resolved new typical absorption bands.•The high temperature treatment can be used for synthesis of new ceramic phosphor materials.