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Author: search.filters.author.Vittayakorn, WanwilaiSubject: search.filters.subject.Dielectric

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    Thermally induced phase transition and dielectric relaxation in lead-free BaTi0.94Sn0.06O3 Ceramics: Insights from in-situ XRD and XAS
    (2025-11-01)
    Sukkha, Usa
    ;
    Chanlek, Narong
    ;
    Kidkhunthod, Pinit
    ;
    Kolodiazhnyi, Taras
    ;
    Vittayakorn, Wanwilai
    Lead-free BaTi<inf>0.94</inf>Sn<inf>0.06</inf>O<inf>3</inf> (BTS) ceramics were synthesized using the conventional solid-state reaction method to investigate thermally induced phase transitions and dielectric relaxation phenomena. A combination of in-situ X-ray Diffraction (XRD) and in-situ Synchrotron X-ray Absorption Spectroscopy (XAS) was employed to examine phase transitions across the temperature range of 200–400 K. The results reveal sequential phase transitions: rhombohedral-orthorhombic (R + O) at 200 K, orthorhombic (O) at 250–300 K, tetragonal (T) at 325–359 K, and tetragonal-cubic (T + C) at 373–400 K. Dielectric measurements highlight an anomalous relaxation behavior at 70–160 K, attributed to domain wall freezing. This phenomenon follows Vogel-Fulcher behavior, with an activation energy of 14 meV, a freezing temperature of 82 K, and an attempt frequency of 4.7 × 10<sup>6</sup> Hz. X-ray Photoelectron Spectroscopy (XPS) analysis reveals oxygen deficiency on the surface of the BTS ceramic, resulting in the coexistence of Ti<sup>3+</sup>/Ti<sup>4+</sup> and Sn<sup>2+</sup>/Sn<sup>4+</sup> oxidation states. These defects significantly influence the dielectric and phase transition properties. This study provides comprehensive insights into the interplay between local structural changes and phase transition mechanisms in BTS ceramics. By employing a multi-technique approach, it advances the understanding of dielectric and ferroelectric behaviors, positioning BTS ceramics as promising candidates for lead-free dielectric and ferroelectric device applications.
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    Interlayer alkali ion governs robustness, reactivity, and dielectric properties of sintered lepidocrocite titanate
    (2022-01-01)
    Maluangnont, Tosapol
    ;
    Pulphol, Phieraya
    ;
    Vittayakorn, Wanwilai
    We investigate the structure across different length scales including the dielectric properties of Cs<inf>0.7</inf>Zn<inf>0.35</inf>Ti<inf>1.65</inf>O<inf>4</inf>, Rb<inf>0.75</inf>Zn<inf>0.375</inf>Ti<inf>1.625</inf>O<inf>4</inf>, and K<inf>0.8</inf>Zn<inf>0.4</inf>Ti<inf>1.6</inf>O<inf>4</inf> sintered at T<inf>S</inf> ​= ​900–1100 ​°C, where the lepidocrocite-type crystal structure is preserved. The increasing interlayer distance in the Rb-/K-analog is explained by the alkali loss which reduces the electrostatic attraction between the sheets and the interlayer ion. Meanwhile, the interlayer contraction in the Cs-analog is rather unusual. The increasing (decreasing) interlayer distances correlate to upshift (downshift) of the Ti-O vibration in the Raman spectra. The three compositions show varied grain orientation depending on the interlayer ion and T<inf>S</inf>. The dielectric permittivity differs by one order of magnitude in the order Cs<inf>0.7</inf>Zn<inf>0.35</inf>Ti<inf>1.65</inf>O<inf>4</inf> « Rb<inf>0.75</inf>Zn<inf>0.375</inf>Ti<inf>1.625</inf>O<inf>4</inf> « K<inf>0.8</inf>Zn<inf>0.4</inf>Ti<inf>1.6</inf>O<inf>4</inf>, suggesting the interlayer ion as the dominating dipole. The influences of T<inf>S</inf>, pellet density (i.e., alkali loss), and grain size/morphology/orientation on the dielectric permittivity are discussed. The understanding of the response to a high temperature treatment would be beneficial not only to specimen fabrications for physical properties measurements, but also to applications where the thermal stability is of concern.
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    Preparation and dielectric properties of 3-3 lead zirconate/polyvinylidene fluoride nanocomposite
    (2013-01-01)
    Nawanil, Chanisa
    ;
    Vittayakorn, Wanwilai
    ;
    Prachayawarakorn, Jutarat
    ;
    Vittayakorn, Naratip
    Composites made of electroactive ceramics and a ferroelectric polymer are very attractive for applications since they exhibit good piezoelectric and pyroelectric properties, low densities and their properties can be tailored to various requirements. Here, we reported the preparation and dielectric properties of 3-3 PZ/PVDF nanocomposites by infusion of polyvinylidenedifluoride (PVDF) into the PZ nanofiber mat followed by heating of the composite at 80°C. The 3-3 PZ/PVDF composites were characterized by X-ray diffraction, FT-IR, SEM and LCR meter. The dielectric constant of the PZ/PVDF nanocomposite are relatively stable in the range of 21.98-18.21 within the measurement frequencies from 100 Hz to 2 MHz. This value is higher than the dielectric constant of the polyvinylidene fluoride. Moreover, the dielectric loss of the composite is below 0.09 at low frequencies. © 2013 Copyright Taylor and Francis Group, LLC.