Modulating the structure,vacancy defects,magnetic and dielectric properties in multiferroic GdMnO3 ceramics by alkaline earth ion substitution

This investigation highlights the significant influences of alkaline earth ion substitution for Gd on the structure, vacancy defects, magnetic and dielectric properties in GdMnO₃ (GMO) ceramics synthesized using the solid-state reaction method. The structure measurements indicate that all of the Gd_0.90A_0.10MnO₃ (A = Ca, Sr, Ba) samples show a single phase structure, and the introduction of A²⁺ ion induces structure distortion. A²⁺ ions substitution increases the Mn⁴⁺ ion concentration in GMOs, but has no significant effect on the oxygen vacancy concentration. All samples with irregular grain shapes have dense microstructures, and A²⁺ ion substitution inhibits grain growth. Positron annihilation experimental results indicate that A²⁺ ion substitution can increase the vacancy size and concentration, while the vacancy concentration increases first and then decreases with increasing A²⁺ ion radius. The evolution of the temperature- and magnetic field-dependent magnetization curves shows that A²⁺ ion substitution could obviously affect the magnetic state of GMOs, and improve the magnetic transition temperature and magnetization of Gd_0.90A_0.10MnO₃. The dielectric measurements reveal that the A²⁺ ion substituted samples exhibit giant dielectric constant characteristics over a broad frequency range. It is found that the enhanced magnetization of Gd_0.90A_0.10MnO₃ has a close relationship with the vacancy concentration, and the giant dielectric constant behaviors in Gd_0.90A_0.10MnO₃ ceramics can be associated with the mixed-valent structure of Mn³⁺/Mn⁴⁺.