Crystallite Size Dependent Polaron Dynamics in α-Fe ₂ O ₃

Polarons are essential for charge transport in oxide semiconductors, considerably impacting the rates of interfacial reactions as well as the redox-driven phase transitions. Here, we employ the broad band impedance spectroscopy to unravel the dynamics of small polaron hopping in hematite (α-Fe2O3), where the concentration of an electron small polaron becomes the temperature and crystallite size (CS) dependent quantity. The temperature dependent dc conductivity (σdc) has been analyzed by using Mott’s model and reveals the non-Arrhenius behavior within the hopping conduction region. The validity of time–temperature superposition principle (TTSP) on frequency dependent conductivity spectra using Summerfield scaling formalism demonstrates deviation in the scaled isotherms. However, the conductivity spectra isotherms were found to scale with a random barrier model, where the temperature dependent variation of polaron concentration is the primary cause for deviations in the TTSP. The polaron dynamics facilitated through a synergistic interplay between CS and concentration of polarons in α-Fe2O3. The temperature dependent polaron concentration is directly supported by the in situ Raman spectroscopy, where we find reduced and structurally distorted metal ion sites consistent with formation of small polarons. The CS dependent polaron-hopping parameters underscore the flexibility of mixing process in low-dimensional systems and suggest new approach for both enhancing and controlling the electron–phonon interaction in oxide semiconductors.