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

Abstract Three different crystal morphologies of α‐Fe 2 O 3 , including uniform hexagonal, square, and rhombic shapes, were prepared according to the aqueous‐thermal reaction. The hexagonal‐shaped α‐Fe 2 O 3 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‐Fe 2 O 3 during analysis by Fourier‐transform infrared spectroscopy. However, the peaks of square‐ and rhombic‐shaped α‐Fe 2 O 3 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‐Fe 2 O 3 , but all peak positions for square‐shaped and rhombic‐shaped α‐Fe 2 O 3 exhibited a significant blueshift. The structure of hexagon‐shaped α‐Fe 2 O 3 was relatively tolerant regarding the polarization properties of vibration modes; however, the symmetry of crystal square‐shaped and rhombic‐shaped α‐Fe 2 O 3 changed, subsequently revealing different optical properties. Research Highlights The hexagon‐shaped, square‐shaped, and rhombic‐shaped α‐Fe 2 O 3 enclosed by different planes were synthesized. The Fourier Transform Infrared spectrometer peaks of α‐Fe 2 O 3 depended on their hexagon, square and rhombic shapes. Compared with hexagon‐shaped α‐Fe 2 O 3 , the Raman peaks for square and rhombi ones significantly shifted. The hexagon‐shaped α‐Fe 2 O 3 is relatively tolerant regarding the polarization properties.