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.