Experimental and theoretical study of nanostructured Ca1-xGdxMnO3 (x=0.05; 0.1; 0.15; 0.2)

Abstract

Experimental and theoretical methods have been used to investigate the octahedral tilting and related effects of Ca1-xGdxMnO3(x = 0.05; 0.1; 0.15; 0.2) compound. Both methods have shown that orthorhombic-perovskite structure (space group Pnma) is the most stable form and according to Glazer's classification belongs to a-b+a- tilt system. Bond valence calculations (BVC) have shown ten additional perovskite-related modifications of the equilibrium Ca1- xGdxMnO3 structure, and their stability has been investigated as function of Gd doping. We have further studied the influence of gadolinium amount on Mn-О bond angles and distances, tilting of MnO6octahedra around all three axes and deformation due to the presence of Jahn- Teller distortion around Mn3+ cation, and calculated the amount of Mn3+ in the system. BVC approach is a simple, fast and efficient way of calculating the amount of Mn4+ and Mn3+ in the doped perovskite compound, which, to the best of our knowledge, has not been done before. The infrared reflection spectra of Ca1-xGdxMnO3 samples confirmed XRD results that Ca1-xGdxMnO3 nanopowders are of Pnma-1 structure and that the tilting of octahedra are increased with Gd doping. The EPR (electron paramagnetic resonance) spectra are in accordance with the assumption that EPR line width is Mn-O-Mn angle dependent. The studied samples showed that small octahedra tilting in these samples brought only a small change of the EPR line width.