Structural, Optical, and Dielectric Properties of Aluminum Oxide Nanofibers Synthesized by a Lower-Temperature Sol–Gel Approach

Abstract

Alumina (Al2O3) is the most versatile and important ceramic material, having applications in various fields including electronic devices. It is stable at high temperatures and is chemically inert. The sol–gel method, a relatively lower-temperature technique, has been used to synthesize aluminum oxide nanofibers. The molarity of the sol concentration was varied as 0.7 M, 0.8 M, 0.9 M, 1.0 M, and 1.1 M. The structural, optical, and dielectric properties of the as-synthesized nanofibers were characterized. x-ray diffraction (XRD) analysis results confirmed formation of α-Al2O3 phase of aluminum oxide, notably without any heat treatment or use of water as solvent. The crystallite size and unit cell volume of the nanofibers increased as the sol concentration was increased to 0.9 M, but further increase in sol concentration resulted in reduction of crystallite size and increase in dislocations. Scanning electron microscopy (SEM) results revealed uniform distribution of nanofibers (∼25 nm to 30 nm) under all conditions. Nanofibers prepared using sol concentration of 0.9 M showed high transmission (∼89%) in the visible and infrared regions. The energy bandgap varied from 3.69 eV to 4.1 eV with the variation in molar concentration. Lower bandgap correlated with defect-induced states in the bandgap. The high refractive index is indicative of high density of aluminum oxide nanofibers. High grain-boundary resistance (1.455 MΩ) and high dielectric constant (∼15.76) along with low tangent loss were observed at molar concentration of 0.9 M.