纳米颗粒NiFe_2O_4的穆斯堡尔谱研究

Mossbauer studies of NiFe_2O_4 nanoparticles

用溶胶凝胶法制备了NiFe2O4纳米晶粉末样品,用XRD表征了样品的晶体结构,用谢乐公式估算了纳米晶粒的尺寸;分别在室温,80 K,9 K采集了样品的穆斯堡尔谱,对样品中超精细场的变化及Fe3+离子在A,B两个晶位的占位情况进行了研究.结果发现随着晶粒尺寸的减小,超精细场变小,Fe3+占据B位的比例增大,纳米颗粒呈现混合型尖晶石结构,不同于块体材料完全反型的尖晶石结构.

Nanocrystalline NiFe204 particles were prepared by sol-gel method. XRD was used to determine the structure, phase purity and particle size. We noticed the variation of the integrated intensity ratio of I(220)/I(222) in XRD patterns. The origin of these phenomena was proposed to be the redistribution of cations between A and B sites in the spinel structure. Further study of Mossbauer spectroscopy confirmed the proposal. Mossbauer spectra were collected at room temperature, 80 K and 9 K, respectively. The variation of the hyperfine magnetic field and the occupancy of cations on A and B sites were studied. It has been found that, with the decrease of the particle size, the population of Fe3+ ions increases on A site and decreases on B site. Measured value of the cation distribution suggests a mixed spinel structure, which is different from the value for the inverse spinel of the bulk material.