LaFeAsO纳米晶的中低温合成与表征

Low-temperature Synthesis and Characterizations of LaFeAsO Nanocrystals

研究了铁基超导母体化合物LaFeAsO的低温固相反应合成及表征。实验以La2O3、LaCl3以及BaFe2As2为原料,通过球磨混合,成功地在中低温（~500℃）下实现固相反应,从而获得LaFeAsO纳米晶。采用X射线衍射Scherrer公式,估算其平均晶粒尺寸小于100 nm。低温电阻测量表明,LaFeAsO纳米晶的自旋密度波反常变得不显著,且其转变温度明显下降。采用晶粒尺寸效应和晶胞参数影响对这种现象进行了解释。

LaFeAsO as a parent compound of iron-based superconductor was synthesized at low temperatures. The mixtures of La203, LaCl3 and BaFe2As2 were ball-milled and the pressed pellets were sintered at 500℃in vacuum. And nanoerystals of LaFeAsO were formed during the solid-state reaction. The solid-state reaction temperature for preparing LaFeAsO is 200℃ lower than the literature reported. The average crystallite size of the as-prepared La- FeAsO is less than 100 nm, as estimated by the X-ray diffraction Scherrer formula. Meanwhile, the c axis of the unit cell is increased by 0.001 nm, primarily stemming from the nanosize effect. Electrical resistivity measurement shows that the spin-density-wave anomaly becomes unremarkable, accompanied by a significant decrease in the transition temperature. The phenomena are discussed in terms of crystallite-size effect and the influence of lattice parameters.