Raman scattering and alternative current conduction mechanism of the different phase transitions in [(CH3)3NH]CoCl3·2H2O

• Published in: Journal of alloys and compounds Vol. 723; pp. 301 - 310
• Main Authors: Kchaou, H., Karoui, K., Bulou, A., Tabellout, M., Ben Rhaiem, A.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 05.11.2017; Elsevier BV; Elsevier
• Subjects: AC conductivity; Alternating current; Chlorides; Cobalt compounds; Complex impedance; Condensed Matter; Conduction mechanism; Conductivity; Dielectric properties; Diffraction patterns; Electrical conduction; Electrical resistivity; Endothermic reactions; Equivalent circuit; Grain boundaries; Hybrid material; Impedance spectroscopy; Materials Science; Nyquist plots; Order disorder; Phase transition; Phase transitions; Physics; Raman spectra; Scattering; Studies; Temperature dependence; Conduction mechanism; Complex impedance; Hybrid material; AC conductivity; Equivalent circuit; Phase transition
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.06.237

The trimethylammonium cobalt chloride dihydrate was obtained by slow evaporation at room temperature. The behavior in accordance with temperature variation was sought. The Rietveld refinement of the X-ray powder diffraction pattern led to the formation of a pure phase which crystallizes in the orthorhombic system with the Pnma space group. Three endothermic peaks at T1=310 K, T2=349 K, and T3=358 K were evidenced by DSC measurements. In order to characterize the phase transitions and their nature, Raman spectra were recorded in the frequency range related to the vibrations of the cations and anions (10−3600 cm−1). The results obtained show the utility of the Raman spectra to probe the changes in T1 and then the reconstruction of new anionic parts after T2 transition. The analysis of the line width based on the order-disorder model was used to obtain information concerning the activation energy near the phase transition at T1. A comprehensive study of the dielectric and electric modulus properties of this compound was conducted using impedance spectroscopy in the frequency range of 100 Hz to 1.3 MHz and over the temperature range of 270 K to 335 K. The analysis of Nyquist plots revealed the presence of grains, grain boundaries and the electrode effects. The modulus plots were characterized by the presence of two peaks associated with grains and grain boundaries. The temperature dependence of the electrical conductivity (σg) and AC conductivity (σac) confirmed the phase transition. The AC electrical conduction in the [(CH3)3NH]CoCl3·2H2O compound underwent two processes attributed to a hopping transport mechanism: the correlated barrier hopping model in region I and the non-overlapping small polaron tunneling model proposed as a closely good model for region II. •Two-phase transitions are evidenced by the DSC and affirmed by Raman spectroscopy.•One phase transition (310 K) is confirmed by the dielectric-electric properties.•The conduction mechanism in our compound is characterized by two processes.