Mechanical alloying synthesis of Sm3NbO7 defect fluorite and structural characterization by X-ray diffraction, Raman spectroscopy and DFT calculation

Abstract

A nanostructured defect-fluorite-type Sm3NbO7 has been produced at ambient temperature by the process of mechanical alloying (MA). The powdered mixture of samarium precursor and pure metallic Niobium (Nb) is milled for 17h to obtain the desired sample with mean crystallite size of 160 Å. The phase transformations induced by the high energy milling have been investigated by ex situ X-Ray Diffraction (XRD) measurements and Rietveld method. The results suggest a symmetrization of Sm(OH)3 crystals induced by Nb solubilization. The Sm3NbO7 microstructures have been examined by Differential Scanning Calorimetry (DSC), heat treatment, Raman spectroscopy and Density Functional Theory (DFT) calculation. The crystallite sizes and defects have been analyzed by Line Profile Analysis utilizing Williamson Hall plot method and Stephens's microstrain model. The anisotropic structural defects caused by MA synthesis disappear under heat treatment with the microstrain reducing from 1.4% to 0.05%.