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<p>In response to the increasing interest in novel tungstate-based materials for optoelectronic applications, the compound Na<sub>4</sub>Mg(WO<sub>4</sub>)<sub>3</sub> was synthesized through a conventional solid-state reaction route employing high-purity WO<sub>2</sub>, Na₂O, and MgO as starting materials. X-ray diffraction (XRD) analysis confirmed the successful formation of a single-phase structure crystallizing in the monoclinic system with space group <i>C2/c</i>. The average crystallite size, calculated using the Scherrer equation, was approximately 58&#xa0;nm. Scanning electron microscopy (SEM) images displayed a microstructure composed of rod-like and prismatic grains with an average size of 0.75&#xa0;μm, then, energy-dispersive X-ray spectroscopy (EDX) verified the uniform elemental distribution of Na, Mg, W, and O, indicative of high purity of the compound. Absorbance measurements confirm the semiconductor character with an indirect band gap energy of 3.37&#xa0;eV. Impedance spectroscopy revealed non-Debye relaxation characteristics, as evidenced by depressed semicircular arcs in the Nyquist plots, which were attributed to the bulk and the grain boundary contributions. Further analysis of the imaginary parts of impedance (<i>Z″</i>) and electric modulus (<i>M″</i>), conducted over the frequency range of 40&#xa0;Hz to 10&#xa0;MHz and temperatures from 423 to 623&#xa0;K, highlighted a thermally activated transition from localized to delocalized charge transport. The <i>AC</i> conductivity (<i>σ</i><sub>ac</sub>) exhibited a positive correlation with the temperature and frequency, ranging from 10<sup>−7</sup> to 10<sup>−3</sup>&#xa0;S&#xa0;cm<sup>−1</sup>, consistent with semiconducting behavior. These results adhered to the Jonscher universal power law, and the temperature-dependent behavior of the power-law exponent <i>s</i> supported the applicability of the correlated barrier hopping (<i>CBH</i>) conduction mechanism. Moreover, the compound exhibited an exceptionally high dielectric constant of approximately <i>ε′&#xa0;</i>≈&#xa0;10<sup>5</sup> at low frequencies and elevated temperatures, along with a low dielectric loss below 320, even at low frequencies. These electrical and dielectric properties, combined with the structural stability of the material, highlight NaMg(WO)<sub>2</sub> as a promising candidate for laser host matrices, high-permittivity components, and energy storage systems.</p>

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Study on structural, morphological, optical and dielectric properties of Na4Mg(WO4)3 triple tungstate

  • 期刊论文

  • 发表日期：

    2025年11月10日

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  • Ines Mbarek,
  • Khawla Ben Brahim,
  • Saber Nasri,
  • Mehdi Akermi,
  • Ridha Djebali,
  • Abderrazek Oueslati

摘要

In response to the increasing interest in novel tungstate-based materials for optoelectronic applications, the compound Na4Mg(WO4)3 was synthesized through a conventional solid-state reaction route employing high-purity WO2, Na₂O, and MgO as starting materials. X-ray diffraction (XRD) analysis confirmed the successful formation of a single-phase structure crystallizing in the monoclinic system with space group C2/c. The average crystallite size, calculated using the Scherrer equation, was approximately 58 nm. Scanning electron microscopy (SEM) images displayed a microstructure composed of rod-like and prismatic grains with an average size of 0.75 μm, then, energy-dispersive X-ray spectroscopy (EDX) verified the uniform elemental distribution of Na, Mg, W, and O, indicative of high purity of the compound. Absorbance measurements confirm the semiconductor character with an indirect band gap energy of 3.37 eV. Impedance spectroscopy revealed non-Debye relaxation characteristics, as evidenced by depressed semicircular arcs in the Nyquist plots, which were attributed to the bulk and the grain boundary contributions. Further analysis of the imaginary parts of impedance (Z″) and electric modulus (M″), conducted over the frequency range of 40 Hz to 10 MHz and temperatures from 423 to 623 K, highlighted a thermally activated transition from localized to delocalized charge transport. The AC conductivity (σac) exhibited a positive correlation with the temperature and frequency, ranging from 10−7 to 10−3 S cm−1, consistent with semiconducting behavior. These results adhered to the Jonscher universal power law, and the temperature-dependent behavior of the power-law exponent s supported the applicability of the correlated barrier hopping (CBH) conduction mechanism. Moreover, the compound exhibited an exceptionally high dielectric constant of approximately ε′ ≈ 105 at low frequencies and elevated temperatures, along with a low dielectric loss below 320, even at low frequencies. These electrical and dielectric properties, combined with the structural stability of the material, highlight NaMg(WO)2 as a promising candidate for laser host matrices, high-permittivity components, and energy storage systems.