The optical properties of nano‐structural α‐Fe2O3 dependence on the shape

Abstract

AbstractThree different crystal morphologies of α‐Fe2O3, including uniform hexagonal, square, and rhombic shapes, were prepared according to the aqueous‐thermal reaction. The hexagonal‐shaped α‐Fe2O3 was enclosed by the 104 plane, while the square and rhombic structures were enclosed by the 110 plane. Two absorption peaks at 455 and 532 cm−1 were found for the perpendicular (⊥) modes, and one absorption peak at 650 cm−1 appeared for the parallel (||) mode for hexagon‐shaped α‐Fe2O3 during analysis by Fourier‐transform infrared spectroscopy. However, the peaks of square‐ and rhombic‐shaped α‐Fe2O3 for perpendicular (⊥) mode blueshifted, and the former two peaks merged together forming a broad band at approximately 480 cm−1.For Raman spectra determination, the peaks arose from the Brillouin zone center, and two additional peaks were observed at 660 and 1320 cm−1, belonging to 1 longitudinal optical (1LO) and 2 longitudinal optical (2LO) modes. All three materials exhibited higher intensities when excited at a wavelength of 633 cm−1. Furthermore, in the polarization state, the centers of all peak positions slightly shifted for hexagon‐shaped α‐Fe2O3, but all peak positions for square‐shaped and rhombic‐shaped α‐Fe2O3 exhibited a significant blueshift. The structure of hexagon‐shaped α‐Fe2O3 was relatively tolerant regarding the polarization properties of vibration modes; however, the symmetry of crystal square‐shaped and rhombic‐shaped α‐Fe2O3 changed, subsequently revealing different optical properties.Research Highlights The hexagon‐shaped, square‐shaped, and rhombic‐shaped α‐Fe2O3 enclosed by different planes were synthesized. The Fourier Transform Infrared spectrometer peaks of α‐Fe2O3 depended on their hexagon, square and rhombic shapes. Compared with hexagon‐shaped α‐Fe2O3, the Raman peaks for square and rhombi ones significantly shifted. The hexagon‐shaped α‐Fe2O3 is relatively tolerant regarding the polarization properties.