Multi-step phase transition crystal with dielectric constant bistability and temperature-dependent conductivity

Area of Science:

• Materials Science
• Solid State Chemistry
• Crystallography

Background:

• Ion-pair compounds are of interest for their diverse physical properties.
• Understanding phase transitions is crucial for developing advanced materials.

Purpose of the Study:

• To investigate the crystal structure, phase transitions, and thermal, dielectric, and conducting properties of [C4-bmim][Ni(mnt)2].
• To explore the mechanisms behind dielectric bistability and temperature-dependent conductivity.

Main Methods:

• Single-crystal X-ray diffraction to determine crystal structures.
• Differential scanning calorimetry (DSC) for thermal analysis.
• Dielectric spectroscopy and conductivity measurements as a function of temperature.

Main Results:

• The compound [C4-bmim][Ni(mnt)2] exhibits a three-step phase transition with four distinct phases before melting.
• Two-step dielectric constant bistability was observed, linked to alkyl chain oscillations and a crystal-to-mesophase transition.
• Rare temperature-dependent conducting properties were found, with high conductivity (0.00186 S cm-1 at 413 K) attributed to dipole molecular motion in the mesophase.

Conclusions:

• The ion-pair compound [C4-bmim][Ni(mnt)2] demonstrates complex structural dynamics and interesting functional properties.
• The observed dielectric bistability and conductivity present potential for applications in electronic devices.