Studies on the dielectric, structural, and electronic properties of barium-doped Gd2NiMnO6 double perovskite

Abstract This study presents a comprehensive exploration of the structural, dielectric, and electronic properties of barium-doped Gd 2 NiMnO 6 (Gd 2-x Ba x NiMnO 6 , with x = 0.0, 0.25, and 0.50) double perovskite compounds synthesized successfully via a conventional solid-state reaction method. Detailed x-ray diffraction (XRD) analysis confirmed the formation of a pure monoclinic phase with space group P21/n for all compositions. Substitution of Gd 3+ with the larger Ba 2+ ions induced systematic expansion of lattice parameters and unit cell volume, verified by Rietveld refinement, demonstrating the structural stability of the double perovskite framework despite significant A-site modification. Field emission scanning electron microscopy revealed a pronounced reduction in grain size with increasing Ba content, attributed to lattice distortion and internal strain, which also influenced the microstructural evolution. Elemental analysis via energy-dispersive x-ray spectroscopy confirmed successful Ba incorporation without impurity phases.Raman spectroscopy showed shifts and broadening of vibrational modes consistent with enhanced lattice disorder and octahedral distortions due to Ba doping, indicative of structural modifications at the local scale. Dielectric studies conducted over a broad frequency (1 Hz to 2 MHz) and temperature (100 K to 300 K) range revealed that the dielectric constant increased significantly with Ba content, mainly driven by enhanced grain boundary effects and increased interfacial polarization arising from reduced grain size. Impedance spectroscopy and AC conductivity measurements indicated thermally activated conduction governed by polaron hopping mechanisms, with Ba doping. Activation energies rose with doping, reflecting decreased carrier mobility due to enhanced lattice distortion and oxygen vacancy formation for charge compensation. This work offers valuable insight into the interplay of doping-induced structural distortion, charge carrier dynamics, and dielectric behavior in double perovskites, enhancing the functional performance and application potential of Gd 2-x Ba x NiMnO 6 materials.