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<p>In this study, a sulfuric acid-assisted ultrasonic approach was employed to synthesize TiO<sub>2</sub> nanomaterials. The synthesized TiO<sub>2</sub> nanostructures exhibited a pure anatase phase with particle sizes in the range of 10–30&#xa0;nm obtained at a calcination temperature of 500&#xa0;°C. These nanomaterials were subsequently utilized for the synthesis of lead-free Bi<sub>0.5</sub>(Na<sub>1−<i>x</i></sub>K<sub><i>x</i></sub>)<sub>0.5</sub>TiO<sub>3</sub> (BNKT<sub>n</sub>, <i>x</i> = 0.15, 0.20, 0.25, 0.30, and 0.35) ceramics. The effect of the K/Na ratio on the structural characteristics, microstructural evolution, morphological features, and electrical properties of BNKT<sub>n</sub> ceramics were systematically studied. In terms of the K/Na ratio range, the ceramics exhibited densely packed grains with a high relative density of 98.2 ± 0.05% (corresponding to 5.87 ± 0.02&#xa0;g/cm<sup>3</sup>), along with a shrinkage ratio of 14.71 ± 0.03%. With a sintering temperature of 1100&#xa0;°C and a K/Na ratio of 0.25/0.75, the BNKT<sub>n</sub> ceramics achieved high electromechanical coupling coefficients (<i>k</i><sub>p</sub> = 0.35 and <i>k</i><sub>t</sub> = 0.39), a large piezoelectric coefficient (<i>d</i><sub>33</sub> = 155 pC/N), and an enhanced dielectric constant (<i>ε</i><sub><i>r</i></sub> = 1191, <i>ε</i><sub>max</sub> = 4335). Additionally, a high mechanical quality factor (<i>Q</i><sub>m</sub> = 145) and a low dielectric loss (tan<i>δ</i> = 0.051) were obtained. The recoverable energy density (<i>W</i><sub>rec</sub>) and ene<i>rgy</i> conversion efficiency (<i>η</i>) increased almost linearly with increasing <i>x</i> content, reaching maximum values of 0.78&#xa0;J/cm<sup>3</sup> and 59.2%, respectively, at <i>x</i> = 0.35. Concurrently, the remanent polarization (<i>P</i><sub><i>r</i></sub>) decreased from 16.1 µC/cm<sup>2</sup> at <i>x</i> = 0.15 to 9.2 µC/cm<sup>2</sup> at <i>x</i> = 0.35.</p>

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Optimization of the K/Na ratio in lead-free Bi0.5(Na1-xKx)0.5TiO3 ceramics utilizing TiO2 nanostructures

  • 期刊论文

  • 发表日期：

    2026年4月30日

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  • Nguyen Trung Duong,
  • Phan Van Hoang,
  • Phan Thi Hong Phuong,
  • Dụng Thị Hoài Trang,
  • Nguyen Van An,
  • Ton Duc Hong,
  • Vo Thi Thanh Kieu,
  • Nguyen Van Nghia,
  • Trinh Ngoc Dat

摘要

In this study, a sulfuric acid-assisted ultrasonic approach was employed to synthesize TiO2 nanomaterials. The synthesized TiO2 nanostructures exhibited a pure anatase phase with particle sizes in the range of 10–30 nm obtained at a calcination temperature of 500 °C. These nanomaterials were subsequently utilized for the synthesis of lead-free Bi0.5(Na1−xKx)0.5TiO3 (BNKTn, x = 0.15, 0.20, 0.25, 0.30, and 0.35) ceramics. The effect of the K/Na ratio on the structural characteristics, microstructural evolution, morphological features, and electrical properties of BNKTn ceramics were systematically studied. In terms of the K/Na ratio range, the ceramics exhibited densely packed grains with a high relative density of 98.2 ± 0.05% (corresponding to 5.87 ± 0.02 g/cm3), along with a shrinkage ratio of 14.71 ± 0.03%. With a sintering temperature of 1100 °C and a K/Na ratio of 0.25/0.75, the BNKTn ceramics achieved high electromechanical coupling coefficients (kp = 0.35 and kt = 0.39), a large piezoelectric coefficient (d33 = 155 pC/N), and an enhanced dielectric constant (εr = 1191, εmax = 4335). Additionally, a high mechanical quality factor (Qm = 145) and a low dielectric loss (tanδ = 0.051) were obtained. The recoverable energy density (Wrec) and energy conversion efficiency (η) increased almost linearly with increasing x content, reaching maximum values of 0.78 J/cm3 and 59.2%, respectively, at x = 0.35. Concurrently, the remanent polarization (Pr) decreased from 16.1 µC/cm2 at x = 0.15 to 9.2 µC/cm2 at x = 0.35.