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<p>We report a comprehensive and constructive investigation into the effects of Na⁺ substitution on the structural, dielectric, and electrical properties of GdMnO<sub>3</sub> (<i>x</i>&#xa0;=&#xa0;0.05, 0.10, and 0.15), synthesized via a high-temperature solid-state reaction method. Through integrated x-ray diffraction and Rietveld refinement analyses, we demonstrate that Na doping systematically modifies the perovskite lattice, leading to a constructive reduction in unit cell volume from 231.636&#xa0;Å<sup>3</sup> (pristine) to 228.137&#xa0;Å<sup>3</sup> (<i>x</i>&#xa0;=&#xa0;0.10), and to a decrease in the average Mn-O-Mn bond angle from 148.63° to 144.80°. These structural adjustments, coupled with a refined grain size (reduced from 169.7&#xa0;nm to 78.0&#xa0;nm) and lower microstrain, directly contribute to enhanced dielectric performance. X-ray photoelectron spectroscopy (XPS) analysis identifies the presence of Mn<sup>3</sup>⁺ and Mn<sup>4</sup>⁺ oxidation states. The proportion of Mn<sup>4</sup>⁺ is 31.50% in 15% doped, 21.94%% in 10% doped, and 12.50% in 5% doped samples, indicating a systematic variation in oxidation states across the samples. Deconvolution of the O 1&#xa0;s spectra identified oxygen vacancies, which play a crucial role in charge compensation and dielectric relaxation. The nearly constant vacancy concentration across all the samples suggests that charge neutrality is predominantly maintained through valence state modulation rather than defect formation. Dielectric spectroscopy reveals two distinct relaxation processes corresponding to intra-grain and grain boundary effects. Arrhenius analysis indicates that the optimally doped <i>x</i>&#xa0;=&#xa0;0.10 sample exhibits the lowest activation energies of 0.182&#xa0;eV for grain relaxation and 0.155&#xa0;eV for grain boundary relaxation, thus constructively facilitating improved charge transport. Complementary impedance spectroscopy, analyzed via Nyquist plots, confirms the dominant role of grain boundary effects by revealing a high grain boundary resistance of approximately 3299&#xa0;Ω, alongside a conduction mechanism governed by localized hopping (<i>n</i>&#xa0;≈&#xa0;0.997). These results establish a direct correlation between Na-induced structural modifications and enhanced dielectric and electrical properties, highlighting the potential of Na-doped GdMnO<sub>3</sub> for applications in dielectric capacitors and resistive switching devices.</p>

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Na+ Substitution in GdMnO3 Multiferroic Oxides: A Gateway to Enhance Structural and Dielectric Properties

  • 期刊论文

  • 发表日期：

    2025年5月13日

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  • Rinku Sarkar,
  • Bidyut Sarkar,
  • Sudipta Pal

摘要

We report a comprehensive and constructive investigation into the effects of Na⁺ substitution on the structural, dielectric, and electrical properties of GdMnO3 (x = 0.05, 0.10, and 0.15), synthesized via a high-temperature solid-state reaction method. Through integrated x-ray diffraction and Rietveld refinement analyses, we demonstrate that Na doping systematically modifies the perovskite lattice, leading to a constructive reduction in unit cell volume from 231.636 Å3 (pristine) to 228.137 Å3 (x = 0.10), and to a decrease in the average Mn-O-Mn bond angle from 148.63° to 144.80°. These structural adjustments, coupled with a refined grain size (reduced from 169.7 nm to 78.0 nm) and lower microstrain, directly contribute to enhanced dielectric performance. X-ray photoelectron spectroscopy (XPS) analysis identifies the presence of Mn3⁺ and Mn4⁺ oxidation states. The proportion of Mn4⁺ is 31.50% in 15% doped, 21.94%% in 10% doped, and 12.50% in 5% doped samples, indicating a systematic variation in oxidation states across the samples. Deconvolution of the O 1 s spectra identified oxygen vacancies, which play a crucial role in charge compensation and dielectric relaxation. The nearly constant vacancy concentration across all the samples suggests that charge neutrality is predominantly maintained through valence state modulation rather than defect formation. Dielectric spectroscopy reveals two distinct relaxation processes corresponding to intra-grain and grain boundary effects. Arrhenius analysis indicates that the optimally doped x = 0.10 sample exhibits the lowest activation energies of 0.182 eV for grain relaxation and 0.155 eV for grain boundary relaxation, thus constructively facilitating improved charge transport. Complementary impedance spectroscopy, analyzed via Nyquist plots, confirms the dominant role of grain boundary effects by revealing a high grain boundary resistance of approximately 3299 Ω, alongside a conduction mechanism governed by localized hopping (n ≈ 0.997). These results establish a direct correlation between Na-induced structural modifications and enhanced dielectric and electrical properties, highlighting the potential of Na-doped GdMnO3 for applications in dielectric capacitors and resistive switching devices.