La/Cu比及分散剂对溶胶-凝胶法制备La_2CuO_4及光学性质的影响

Influences of La/Cu molar ratio and dispersant on the preparation and optical property of La_2CuO_4 crystallites synthesized by sol-gel process

采用溶胶-凝胶法,以硝酸镧和硝酸铜为原料,在不同La/Cu物质的量比条件下合成了La2CuO4粉体。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和紫外-可见-近红外光谱(UV-Vis-Nir)对样品的物相组成、显微形貌以及光学性能进行了分析。结果表明,n(La)/n(Cu)比为化学计量比2∶1时,可以制备出单一相的La2CuO4;n(La)/n(Cu)<2∶1时,产物含有CuO杂质相;n(La)/n(Cu)>2∶1时,含有La2O3杂质相。根据UV-Vis-Nir光谱分析,n(La)/n(Cu)为2∶1,所得La2CuO4的光学带隙为1.37eV,杂质相的产生使光学带隙减小。以抗坏血酸、葡萄糖为分散剂,有较好的分散效果,聚乙二醇作为分散剂时,出现团聚现象,相应的光学带隙分别为1.39、1.41和1.33eV。

La2CuO4 crystallites were prepared via a sol-gel process using lanthanum nitrate and cupric nitrate as raw materials with different La/Cu molar ratios. The phase composition, microstructure and optical property of the as-prepared La2CuO4 powders were characterized by X-ray diffraction, scanning electron microscope and UV-Vis-NIR spectrophotometer. The results show that pure La2CuO4 crystallites can be obtained when La/Cu molar ratio corresponds with the stoichiometrie ratio （2 ： 1）. CuO or La2O3 impurity phase can be detected when the La/Cu molar ratio was lower or higher than the stoichiometric ratio. According to UV-Vis-NIR spec- tral analysis, the optical band gap was 1.37eV when La/Cu molar ratio was 2： 1, while it decreases along with the appearance of impurity phase. With ascorbic acid or ghlcose as dispersant, the dispersity of the producls was improved. Using polyethylene glycol as dispersant, the reunion phenomenon appears. And the correspond ing optical band gap was 1.39, 1.41 and 1.33eV, respectively.