Molecular dynamics and phase transitions in tris(dimethylammonium) enneaiododibismuthate (III) as studied by DSC, dilatometric, IR, ¹H NMR and dielectric methods

Abstract

The phase transitions and molecular motions of the cations were studied in the temperature range 130–300 K in a [(CH₃)₂NH₂]₃Bi₂I₉ (DMAIB) crystal by DSC, IR, dilatometric, dielectric and ¹H NMR methods. It was confirmed that DMAIB undergoes three phase transitions at T _c1 = 305 K, T _c2 = 285 K and T _c3 = 235 K. In the high-temperature phases I–II the cations undergo isotropic reorientations, and in phases III–IV both C₃(CH₃) motion and n-fold ionic reorientations take place.

Key Words:

• Alkylammonium halogenobismuthates
• phase transitions
• infrared
• dielectric
• thermal expansion
• NMR