Comprehensive analysis of antimony-based organic–inorganic hybrid material: phase transition, Raman scattering, and the electrical conduction mechanism of [(CH3)4P]3Sb2Br9

Abstract

The present work focuses on elucidating the origin of the phase transition in [(CH₃)₄P]3Sb₂Br₉ and its associated electrical properties. The compound was synthesized by slow solvent evaporation at constant temperature and characterized using X-ray powder diffraction, FTIR spectroscopy, temperature-dependent Raman spectroscopy, and impedance spectroscopy. XRD confirmed the formation of a monoclinic structure with the polar P3₁c space group. Complementary FTIR and Raman analyses enabled the assignment of vibrational modes at room temperature, providing a reliable reference for monitoring temperature-induced phase transitions. Raman spectra collected between 294 and 563 K revealed specific molecular displacements and reorientations of both organic and inorganic components associated with the transition near 540 ± 7 K. Impedance spectroscopy in the 433–563 K range displayed a single semicircle in the Nyquist plots, evidencing a grain-dominated electrical response. The impedance data were successfully modeled by an equivalent circuit comprising a resistance in parallel with a constant phase element. Both ac and dc conductivities were analyzed to clarify the conduction mechanisms, with charge transport found to obey Jonscher's power law and consistent with the Correlated Barrier Hopping (CBH) and Non-overlapping Small Polaron Tunneling (NSPT) models. [(CH₃)₄P]₃Sb₂Br₉ shows both phase transition and ionic conduction, highlighting its potential in memory devices, electrolytes, light-harvesting, and energy applications.