Ferroelastic phase transition and dielectric anomalies in 2,4,6-trimethylanilinium perchlorate

Abstract

The crystal structure of the crystalline 1 : 1 complex of 2,4,6-trimethylaniline with perchloric acid, (C₉H₁₄N)⁺·ClO₄⁻ (1), was determined at 25 °C and 110 °C, respectively. The crystal structural analysis of both temperatures show that 1 undergoes a reversible phase transition from triclinic P (No.2) to monoclinic P2₁/m (No.11) with a distinct change of the cell parameters. It is a ferroelastic phase transition with an Aizu notation of 2/mF. DSC (differential scanning calorimetry) measurement confirms that this compound undergoes a reversible first-order solid-state structural phase transition at about 48 °C with a thermal hysteresis of 3 °C. Usually, phase transition is accompanied by an anomaly of the dielectric constant near phase transition temperature (T_c). The DSC measurement, temperature-dependent single-crystal X-ray diffraction and dielectric studies reveal that 1 displays structural phase transitions and distinctly step-like dielectric anomalies at 48 °C probably supporting that this phase transition is of the first-order.