Structures and magnetic properties of nanocomposite CoFe_2O_4-BaTiO_3 fibers by organic gel-thermal decomposition process

The nanocomposite xCoFe2O4-(1-x)BaTiO3(x=0.2,0.3,0.4,0.5,molar fraction) fibers with fine diameters and high aspect ratios(length to diameter ratios) were prepared by the organic gel-thermal decomposition process from citric acid and metal salts.The structures and morphologies of gel precursors and fibers derived from thermal decomposition of the gel precursors were characterized by Fourier transform infrared spectroscopy,X-ray diffractometry and scanning electron microscopy.The magnetic properties of the nanocomposite fibers were measured by vibrating sample magnetometer.The nanocomposite fibers consisting of ferrite(CoFe2O4) and perovskite(BaTiO3) are formed at the calcination temperature of 900 ℃ for 2 h.The average grain sizes of CoFe2O4 and BaTiO3 in the nanocomposite fibers increase from 25 to 65 nm with the calcination temperature from 900 to 1 180 ℃.The single fiber constructed from these nanograins of CoFe2O4 and BaTiO3 has a necklace-like morphology.The saturation magnetization of the nanocomposite 0.4CoFe2O4-0.6BaTiO3 fibers increases with the increase of CoFe2O4 grain size,while the coercivity reaches a maximum value when the average grain size of CoFe2O4 is around the critical single-domain size of 45 nm obtained at 1 000 ℃.The saturation magnetization and remanence of the nanocomposite xCoFe2O4-(1-x)BaTiO3(x=0.2,0.3,0.4,0.5) fibers almost exhibit a linear relationship with the molar fraction of CoFe2O4 in the nanocomposites.

N719染料敏化BaTiO3@TiO2纳米复合电极的制备及性能研究

BaTiO3是非常常见的铁电材料,经常用于制备铁电光伏器件或与半导体器件相结合来优化光伏器件的光电性能。采用水热法合成了BaTiO3纳米颗粒,并在FTO玻璃上制备了BaTiO3纳米晶薄膜,通过TiCl4水溶液后处理的方法在BaTiO3纳米薄膜上形成不同厚度的TiO2层,利用XRD、SEM和TEM分别对BaTiO3@TiO2纳米复合薄膜的物相和形貌进行了表征。将此电极经N719染料敏化后作为染料敏化太阳能电池的光阳极,并进行了光电性能测试。研究结果表明,水热法制备的BaTiO3薄膜晶型为四方相,呈球形多孔,平均粒径约50 nm;经过TiCl4后处理,在BaTiO3薄膜表面形成了锐钛矿相的TiO2颗粒。180℃下水热合成的BaTiO3纳米颗粒经过4次TiCl4后处理制备成的染料敏化太阳能电池取得了最优性能,其光电流密度9.78 mA cm-2,开路电压765 mV,填充因子76.1%和光电转换效率5.69%。