Size-tunable synthesis and structure analysis of BaMnO3 nanorods

The perovskite BaMnO₃ nanorods with fixed width of 60-100-nm and tunable length of 600-800-nm, 400-600-nm and 150-300-nm have been prepared by using a composite-hydroxide-mediated method with adding 0, 3 and 7-ml H₂O. The ratio of surface area to volume (SVR) increases with decreasing length of the nanorods. The X-ray diffraction pattern of the nanorods indexes a hexagonal phase BaMnO₃ with space group P6₃/mmc. Two absorption peaks are observed in ultraviolet-visible absorption spectra measured on the BaMnO₃ nanorods at room temperature. The peak centred at 402 nm is sensitive to length of the nanorods. The band and density of states of BaMnO₃ are calculated by density-functional theory. The results show that the peak centred at 402 nm is assigned to a transition of 2P↓to Mn t_2g↓states, while the peak centred at 301nm is corresponding to the O 2P↑ to Mn e_g↑ states. The increasing of SVR brings the more oxygen surface layer areas and oxygen vacancies, which decreases the bandgap, and leads to the red shift of emission and weakening of the absorption peak centred at 402 nm.