Determination of antisite defects in double perovskite Sr 2FeMoO 6 by diffraction method: Simulation studies

Abstract

The crystal structure of double perovskite Sr 2FeMoO 6 synthesized via solid-state reaction at 1280 °C under a reduction atmosphere is refined by Rietveld technique based on X-ray powder diffraction (XRD) data in 2 θ range of 15–140°. An antisite content (AS), i.e. Fe on the Mo sites (=Mo on the Fe sites), of 12.1(1)% is derived. In reference to the refinement results, a series of X-ray and neutron powder diffraction (NPD) data with different antisite contents, ranging from 0 (completely ordered) to 50% (completely disordered), are generated with a Poisonian noise added and subjected to Rietveld refinements with the same initial values for the refinable parameters. The AS is reproduced satisfactorily from the refinement of XRD data and the combined refinement of XRD and NPD data with a relative deviation smaller than 4%, whereas the relative deviation of AS derived from the refinement of NPD data can be as large as 50%. However, the atomic occupancies and isotropic temperature factors of all the atoms can be reasonably reproduced from the refinement of NPD data and the combined refinement of XRD and NPD data, whereas these data can be reproduced only for cations (Sr, Fe, Mo) from the refinement of XRD data. The present simulation studies shed light on understanding the controversial statements derived from XRD and NPD work regarding the antisite defects in Sr 2FeMoO 6, which in turn is indispensable for understanding the mechanism of large room temperature low-field magnetoresistance of the compound.