Optical and electrical properties and conduction mechanism of [(CH3)2NH2]2CoCl4

Monoclinic crystals of [(CH₃)₂NH₂]₂CoCl₄ are of the space group P2₁/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 [(CH₃)₂NH₂]₂CoCl₄ was studied in the frequency range 10⁻¹–10⁶ 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 + A₁ω^s1 + A₂ω^s2. Accordingly, the first AC term A₁ω^s1 corresponds to translational hopping motion and the second term A₂ω^s2 to well-localized hopping and/or reorientational motion. Conduction takes place via correlated barrier hopping in phases I and II.