Structural refinement of Nd[Fe(CN)6].4 H2O and study of NdFeO3 obtained by its oxidative thermal decomposition at very low temperatures

Abstract

The crystal structure of Nd[Fe(CN)6].4H2O has been refined by Rietveld analysis using high resolution synchrotron powder Xray diffraction data. It belonged to the orthorhombic crystal system, Cmcm space group, with cell parameters: a = 7.473952(1) Å; b = 12.919104(2) Å and c = 13.800549(2) Å. The change in space group from P63/m which is observed in the pentahydrates (LnFe(CN)6.5H2O) to Cmcm in the tetrahydrates has been analyzed to be a consequence of the change in 9-fold coordination of Nd3+ in the pentahydrates to 8-fold coordination in the tetrahydrates, which changes the Nd3+ environment from tricapped trigonal prism to a distorted tricapped trigonal prism or square antiprism. Its decomposition process in air to produce NdFeO3 has been followed by thermogravimetric and differential thermal analysis, IR spectroscopy and laboratory powder XRD. We found that it is possible to synthesize crystalline NdFeO3 at temperatures as low as 380o C and refine the structure of single phase crystalline NdFeO3 synthesized by this method at 600o C.