First-principles study of organically modified muscovite mica with ammonium (NH$_4^+$) or methylammonium (CH$_3$NH$_3^+$) ion

TL;DR

This study uses density functional theory to analyze how interlayer cation exchange affects muscovite mica's structure and electronic properties, revealing minimal impact on insulation and energetics of exchange with ammonium and methylammonium ions.

Contribution

It provides a first-principles investigation of cation exchange effects on muscovite mica's structure and electronic properties, highlighting the preservation of insulating behavior.

Findings

Unit cell volume remains nearly unchanged with NH₄⁺ exchange.

Unit cell expands by about 4% with CH₃NH₃⁺ exchange.

Band gap remains around 5 eV after exchange, maintaining insulation.

Abstract

Using density functional theory calculations, we have investigated the interlayer cation exchange phenomena in muscovite mica, which is motivated by a necessity to develop flexible high-insulating covering materials. The crystalline structures, chemical bonding properties, energetics, and electronic properties of muscovites before and after exchange of interlayer K$^+$ cation with ammonium (NH$_4^+$) or methylammonium (CH$_3$NH$_3^+$) ion were calculated. It was found that the unit cell volume changes are negligibly small upon exchange with NH$_4^+$ ion, while the unit cells are expanded with about 4 \% relative rate when replacing the interlayer K$^+$ cation with CH$_3$NH$_3^+$ ion. The energy band gap of pre-exchanged muscovite was calculated to be about 5 eV, which hardly changes upon interlayer cation exchange with either NH$_4^+$ or CH$_3$NH$_3^+$ ion, indicating the preservation of high insulating property of muscovite. The exchange energies were found to be about -100 kJ/mol for NH$_4^+$ and about -50 kJ/mol for CH$_3$NH$_3^+$ exchange, indicating that the exchange reactions are exothermic. A detailed analysis of atomic resolved density of states and electron density redistribution was provided.