Influence of oxygen defects on the crystal structure and magnetic properties of the (Tb_1-xNa_x)MnO_3-y (0 ≤ x ≤ 0.3) system

The crystallographic and magnetic behaviors of (Tb_1-xNa _x)MnO_3-y (0 ≤ x ≤ 0.3) have been studied by neutron powder diffraction (NPD), synchrotron X-ray powder diffraction, and Raman spectroscopy techniques. Although Na⁺ ions have larger ionic radii than Tb³⁺ ions, analysis of NPD data reveals a decrease in cell volume upon Na-doping, which can be explained solely by the occurrence of oxygen deficiencies and not by the size effect. The Raman spectrum represents the variation in bond length and bond angle, which originates from the balance of ions, asymmetric structure, and defects in the system. Na-doping causes an oxygen deficiency, and consequently, a peak shift is seen in the Raman spectrum because of the structural adjustment resulting from the doping. The observed effective moments decrease with increasing x because of the replacement of Tb³⁺ ions by Na⁺ ions. The well-defined peak at ∼45 K (labeled T_Mn) of the x = 0.3 sample is associated with Mn spin ordering, while the magnetic responses associated with T_Mn are not clearly present in the x = 0.15 and x = 0 samples.