Crystal structure and magnetic characterization of NaxNd1-xMnO3 obtained by mechanosynthesis

Abstract

In this work are reported results of crystal structure analyses and magnetic properties of Na_xNd_1-xMnO_3, (0<x<0.3, Dx=0.05) obtained by mechanosynthesis. Stoichiometric mixture of metallic oxides Mn₂O₃, Nd₂O₃ and Na₂O were milled using a highball mill up to 300 min. X-ray powder diffraction and Rietveld refinement were used to monitor the phase transformation as a function of the milling time and composition, while the technique vibrating sample magnetometry, VSM, was used to magnetically characterized the powders. The results show that it is possible to obtain the manganites with rhombohedral perovskite structure R3c directly by mechanosynthesis, using a weight ratio of balls to powder of 10:1. After 270 min. of milling time, the synthesis is completed; the time is independent of the sodium-doping level. However, increase of the Na⁺ content leads to a distortion of the crystal structure which modified the magnetic properties. The specific magnetization increases when the manganite is doped, showing a maximum for x=0.10, which is associated with the heterovalent substitution of Na⁺ by Nd³⁺ that causes vacancies and structural distortions due to differences in radii and charge.