Evolution of structure, vacancy characteristics, dielectric and magnetic properties of GdMnO3 ceramics induced by Li+ ion substitution

This work studies the influences of Li ⁺ ion substitution for Gd on the structure, vacancy characteristics, magnetic and dielectric properties in GdMnO ₃ ceramics prepared by solid-state method. XRD measurements indicate that all of the Gd _{1- x}Li _xMnO ₃ ceramics show single phase structure, the introduction of Li ⁺ ions induces structure distortion. XPS results show that Li ⁺ ions substitution introduces more Mn ⁴⁺ in GdMnO ₃, while has no significant effect on oxygen vacancy concentration. Positron annihilation experimental results indicate that the vacancies concentration increases first and then reduces with increasing Li ⁺ ions content. The evolution of the temperature- and magnetic field-dependent magnetization curves presents that the magnetic transition temperature and magnetization of Gd _{1- x}Li _xMnO ₃ could obviously be improved by Li ⁺ ion substitution. Dielectric measurements reveal that the Li ⁺-substituted samples exhibit giant dielectric constant characteristics over a broad frequency range. It is found that the enhanced magnetization of Gd _{1- x}Li _xMnO ₃ has a close relationship with vacancies concentration, and the giant dielectric constant behaviors of Gd _{1- x}Li _xMnO ₃ ceramics can be associated with the mixed-valent structure of Mn ³⁺/Mn ⁴⁺ and < Mn-O-Mn > bond angle.