Structural and optical properties of α aluminum oxide prepared by sol-gel method

Abstract

Aluminum oxide (Al₂O₃) powders were prepared via sol-gel method. The samples underwent three-hours of calcination process between 1100 and 1200° C. An X-ray diffraction (XRD) was used to analyze structural properties, field emission scanning electron microscopy (FE-SEM) was employed to assess morphological characteristics, UV–visible (UV/vis) and Raman spectroscopies were used for determining the optical properties. According to the XRD data, the samples display α- Al₂O₃ type in the hexagonal structure. As the calcination temperature increases, the lattice parameters of both samples remain unchanged, recording values of a = 4.76 ± 0.10 Å and c = 12.98 ± 0.10 Å. The crystalline size increases from 35.0 ± 0.1 to 38.0 ± 0.1 nm as calcination temperature increases from 1100 to 1200 °C, respectively. At 1100 °C the sample shows the presence many pores mixed with needles-like structures; with a further increase in the calcination temperature to 1200 °C, the sample shows large and porous particles. There is no change in the energy gap with increasing calcination temperatures; their values of 3.8 and 4.5 eV are recorded. This could be due to the Al₂O₃ being stable at high calcination temperature. Raman spectra of both samples showed the active mode A1g located at 415 and 643 cm⁻¹ and the other Raman active mode of Eg located at 376, 429, 575 and 749 cm⁻¹, these results are close to Raman spectra for single crystalline α-Al₂O₃ but with slight differences in Raman peak positions which could be due to the disorder vibration of active phonon.

sanalysis are also discussed.