Preparation Of Perovskite Manganese Oxides (BaMnO₃,BaTi_0.5Mn_0.5O₃) By CHM Method

In recent years, Mn-based perovskite oxides has been investigated for its giant magnetoresistive effect extensively. But other properties related to this material were poorly investigated, In this paper, we choose BaMnO₃ and BaTi_0.5Mn_0.5O₃ nano-crystals as the objects of study. Their preparation, gas-sensing and optical properties. Among these, the research of BaMnO₃ gas sensors and the principle of gas sensitive have important significance in the preparation of high sensitivity and selectivity, response, quick recovery of gas sensorsIn this study, we developed a novel simple method-composite-hydroxide-mediated (CHM) route to synthesize well crystallized, highly pure BaMnO₃ and BaTi_0.5Mn_0.5O₃ nanocrystals. The synthesis technology used here requires only low synthesis temperature and normal pressure, which is beneficial for mass-production with low costs.As-synthesized BaMnO₃ crystals by the CHM are uniform, well dispersed nanorods, which have a hexagonal polymorph structure with widths of 50-100 nm, and the lengths of 500-1000nm. Experimental results indicated that the nanorods could be transferred into nanoparticles with adding a small amount of deionized water. On the other hand, the BaTi_0.5Mn_0.5O₃ elliptical nanorods can be obtained by the CHM method by substituting half Mn ions by half Ti ions. Typical nanorods have widths ranging from 20 to 50nm, and lengths from 100 to 500 nm. The form mechanism of the nanorods is proposed according to coordination polyhedron growth theory and coordination polyhedron growth habit rule. Meanwhile, the morphology difference between BaMnO₃ and BaTi_0.5Mn_0.5O₃ is also discussed.The synthesized BaMnO₃ materials are made into film electrode and the gas sensitivity experiments are carried out in O₂ and N₂. The conductance-temperature curves are investigated, there is a conductance peak around 275℃in O₂ atmosphere, while the conductance increases lineally when the electrode exposes to N₂, which matches the characteristic of semi-conductor electrical conductivity, indicating N₂ does not affect the electrical property of BaMnO₃ nanorods. And the cause of the above mentioned phenomenon is analyzed. The resistance of BaMnO₃ increases when it exposes to the electron donating gas of O₂, it shows the typical n-type electric conducting characterization. In addition, UV-vis spectrum of BaMnO₃ is investigated using a UV-vis spectrophotometer.