Excitation-dependent photoluminescence, conduction mechanisms via Impedance spectroscopy, and DRT investigations in Al-doped ZnO ceramics

Abstract

This study presents the synthesis and comprehensive characterization of Al-doped ZnO (AZO) ceramics, emphasizing their structural, dielectric, and electronic properties. A novel contribution of this work is the first detailed correlation of ZnO's impedance behavior with the Distribution of Relaxation Times (DRT), providing deeper insights into charge carrier dynamics. AZO ceramics were synthesized using a reduction method. X-ray diffraction (XRD) coupled with Rietveld refinement confirmed the formation of a single-phase wurtzite structure. Field-emission scanning electron microscopy (FESEM) revealed dense microstructures, with AZO2 exhibiting the largest average grain size of 0.50 μm. Temperature-dependent dielectric measurements revealed two prominent dielectric anomalies across all compositions, with AZO6 showing a maximum dielectric constant of 74,400 at 5 kHz. Impedance spectroscopy and DRT analysis indicated distinct thermal conduction mechanisms, with conduction in ZnO and AZO6 governed by the correlated barrier hopping (CBH) model, whereas AZO2 and AZO4 followed the non-overlapping small polaron tunneling (NSPT) model. AZO2 exhibited the highest saturation (Ps = 27.74 μC/cm²) and remanent polarization (Pr = 25.56 μC/cm²). Optical bandgaps ranged from 3.000 to 3.044 eV. Excitation-dependent photoluminescence studies revealed chromaticity shifts from cyan to French blue, demonstrating tunable optical properties. These findings position AZO ceramics as promising candidates for advanced electronic and optoelectronic applications.