Optical and electrical properties and conduction mechanism of [(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>]<sub>2</sub>CoCl<sub>4</sub>
Nadia Mahfoudh, K. Karoui, M. Gargouri, A. BenRhaiem
Abstract
Monoclinic crystals of [(CH 3 ) 2 NH 2 ] 2 CoCl 4 are of the space group P2 1 /n. Unit cell dimensions are as follows: a = 8.5393 Å, b = 11.3905 Å, c = 13.4069 Å and β = 91.02°. This compound undergoes several phase transitions. The optical properties were measured by means of UV–visible absorption spectroscopy in the range 200–800 nm. Analysis of the data revealed the existence of direct allowed optical transition mechanisms with bandgap energy equal to 3.84 eV. The electrical conductivity of [(CH 3 ) 2 NH 2 ] 2 CoCl 4 was studied in the frequency range 10 −1 –10 6 Hz and in the temperature range 411–449 K by means of impedance spectroscopy. Impedance and modulus analyses indicated temperature‐independent distribution of relaxation times and non‐Debye behavior in this material. A super‐linear power law was observed for the AC conductivity, which was analyzed based on the jump relaxation model σ ac = σ dc + A 1 ω s1 + A 2 ω s2 . Accordingly, the first AC term A 1 ω s1 corresponds to translational hopping motion and the second term A 2 ω s2 to well‐localized hopping and/or reorientational motion. Conduction takes place via correlated barrier hopping in phases I and II.