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<p>In the present work, coarse- and fine-grained ceramics of Li<sub>0.05</sub>Ti<sub>0.02</sub>Ni<sub>0.93</sub>O (NLTO) materials have been prepared by conventional and spark plasma sintering techniques, and their dielectric performance has been investigated. NLTO nanopowder has been prepared by solid state reaction and mechanical milling with a particle size of 49&#xa0;nm. Coarse grained NLTO ceramics have been prepared by conventional sintering at 1240&#xa0;°C for 5&#xa0;h (CS-1240), whereas the fine grained ceramics were prepared by spark plasma sintering (SPS) at different temperature of 900&#xa0;°C, 1000&#xa0;°C and 1100&#xa0;°C for various dwelling times. The obtained materials were characterized by XRD, and the Rietveld analysis confirms the cubic NiO structure, with minor impurity phase of TiO<sub>2</sub>. From SEM experiments, the CS-1240 ceramics have average grain size of ~ 2.45&#xa0;µm, whereas the average grain size of the SPS ceramics is substantially reduced to 70&#xa0;nm, 103&#xa0;nm, and 113&#xa0;nm after SPS at 900, 1000 and 1100&#xa0;°C, respectively for 5&#xa0;min. EDS spectra confirmed the compositions of the materials and showed that Ti dopants are preferably located in the grain boundary layers. All of the investigated ceramics exhibit giant dielectric constant with the CS-1240 ceramic having the highest value of ε′ ~ 3.9 × 10<sup>4</sup> at 10&#xa0;kHz that is 2 – 5 folds higher than previous studies. The value of ε' for the SPS nanoceramics is almost one order smaller with a value of 2.02 × 10<sup>3</sup> – 4.70 × 10<sup>3</sup>. Increasing the SPS dwelling time to 10 and 15&#xa0;min at 1000&#xa0;°C led to increasing the average grain size to 110&#xa0;nm and 117&#xa0;nm, respectively, and increasing the dielectric constant of the materials. The impedance data have been analyzed and the electrical conductivity of the grain interiors and the grain boundary layers and the activation energy of conduction have been estimated. The grain conductivity of NLTO ceramics is four orders of magnitude larger than the conductivity of grain boundary layers, indicating electrical heterogeneous structure. Therefore, the electrical and dielectric properties of NLTO ceramics could be interpreted based on the internal barrier layer capacitance (IBLC) model.</p>

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Enhanced dielectric performance of coarse- and fine-grained Li0.05Ti0.02Ni0.93O ceramics prepared via conventional and spark plasma sintering

  • 期刊论文

  • 发表日期：

    2025年10月9日

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  • Mohamad M. Ahmad,
  • Hicham Mahfoz Kotb,
  • Nagih M. Shaalan,
  • Yohei Yamane,
  • Mir Waqas Alam,
  • Hassan A. Khater

摘要

In the present work, coarse- and fine-grained ceramics of Li0.05Ti0.02Ni0.93O (NLTO) materials have been prepared by conventional and spark plasma sintering techniques, and their dielectric performance has been investigated. NLTO nanopowder has been prepared by solid state reaction and mechanical milling with a particle size of 49 nm. Coarse grained NLTO ceramics have been prepared by conventional sintering at 1240 °C for 5 h (CS-1240), whereas the fine grained ceramics were prepared by spark plasma sintering (SPS) at different temperature of 900 °C, 1000 °C and 1100 °C for various dwelling times. The obtained materials were characterized by XRD, and the Rietveld analysis confirms the cubic NiO structure, with minor impurity phase of TiO2. From SEM experiments, the CS-1240 ceramics have average grain size of ~ 2.45 µm, whereas the average grain size of the SPS ceramics is substantially reduced to 70 nm, 103 nm, and 113 nm after SPS at 900, 1000 and 1100 °C, respectively for 5 min. EDS spectra confirmed the compositions of the materials and showed that Ti dopants are preferably located in the grain boundary layers. All of the investigated ceramics exhibit giant dielectric constant with the CS-1240 ceramic having the highest value of ε′ ~ 3.9 × 104 at 10 kHz that is 2 – 5 folds higher than previous studies. The value of ε' for the SPS nanoceramics is almost one order smaller with a value of 2.02 × 103 – 4.70 × 103. Increasing the SPS dwelling time to 10 and 15 min at 1000 °C led to increasing the average grain size to 110 nm and 117 nm, respectively, and increasing the dielectric constant of the materials. The impedance data have been analyzed and the electrical conductivity of the grain interiors and the grain boundary layers and the activation energy of conduction have been estimated. The grain conductivity of NLTO ceramics is four orders of magnitude larger than the conductivity of grain boundary layers, indicating electrical heterogeneous structure. Therefore, the electrical and dielectric properties of NLTO ceramics could be interpreted based on the internal barrier layer capacitance (IBLC) model.