Low-temperature Synthesis and Characterizations of LaFeAsO Nanocrystals

LaFeAsO as a parent compound of iron-based superconductor was synthesized at low temperatures. The mixtures of La2O3, LaCl3 and BaFe2As2 were ball-milled and the pressed pellets were sintered at 500 degrees C in vacuum. And nanocrystals of LaFeAsO were formed during the solid-state reaction. The solid-state reaction temperature for preparing LaFeAsO is 200 degrees C lower than the literature reported. The average crystallite size of the as-prepared LaFeAs0 is less than 100 nm, as estimated by the X-ray diffiaction 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.