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Author: search.filters.author.Kaewsit, SriwanSubject: search.filters.subject.Dielectric properties

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    Effect of quenching technique on electrical properties of KNN ceramics
    (2026-05-01)
    Sompong, Khanisorn
    ;
    Kaewsit, Sriwan
    ;
    Parjansri, Piewpan
    ;
    Pengpat, Kamonpan
    ;
    Yongsiri, Ploypailin
    Cooling rate during sintering constitutes a critical yet systematically underexplored processing variable that governs defect thermodynamics, microstructural evolution, and functional performance in lead-free K<inf>0.5</inf>Na<inf>0.5</inf>NbO<inf>3</inf> (KNN) piezoelectric ceramics. This study establishes quantitative processing-structure-property relationships by systematically comparing two contrasting post-sintering thermal trajectories controlled slow cooling (S-SC) and rapid quenching (S-Q) across sintering temperatures of 1050-1130 °C. Phase-pure KNN ceramics were synthesized via conventional solid-state reaction incorporating 3 mol% excess alkali carbonates and subsequently sintered for 3 h. Structural and microstructural characterization was conducted by X-ray diffraction, scanning electron microscopy, and Archimedes bulk density measurements. Dielectric and ferroelectric responses were evaluated as functions of both sintering temperature and cooling protocol. S-SC processing at 1130 °C yielded synergistic microstructural improvements bulk density of 4.33 g/cm3 (+12.5% relative to 1050 °C), XRD-derived crystallinity of 62% (+24%), and mean grain size of 11.44 μm, that collectively suppressed point-defect concentration through three concurrent mechanisms: elimination of pore-associated extrinsic defect sites, reduction of intrinsic oxygen vacancies (V_O••) via extended thermally activated annihilation, and diminished grain boundary area available for preferential defect segregation. These microstructural advances directly translated into superior dielectric permittivity (εᵣ = 350 at 1 kHz) and remanent polarization (Pᵣ = 0.65 μC/cm2). Conversely, S-Q processing kinetically arrested oxygen vacancy migration and preserved metastable high-temperature domain configurations, yielding competitive permittivity (εᵣ = 242) and enhanced thermal stability at moderate sintering temperatures (1080 - 1100 °C), despite comparatively reduced crystallinity and bulk density. Both thermal protocols preserved the orthorhombic perovskite structure; however, the optimum cooling strategy is demonstrably temperature-dependent. The present findings provide a mechanistic defect-thermodynamic framework and evidence-based thermal processing guidelines for the rational design of high-performance lead-free KNN-family piezoelectric ceramics.
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    Electrical and magnetic properties of BSFO-NZF multiferroic composite ceramics
    (2025-06-01)
    Kaewsit, Sriwan
    ;
    Sompong, Khanisorn
    ;
    Pairindra, Worapong
    ;
    Pengpat, Kamonpan
    ;
    Yongsiri, Ploypailin
    This study involves the characterization and synthesis of (1-x)Bi<inf>0.9</inf>Sm<inf>0.1</inf>FeO<inf>3</inf> (BSFO) in association with (x)Ni<inf>0.6</inf>Zn<inf>0.4</inf>Fe<inf>2</inf>O<inf>4</inf> (NZF) multiferroic composite ceramics, utilizing x ratios of 0.0, 0.1, 0.3, 0.5, 0.7, and 1.0, achieved through the high-energy planetary ball milling technique and conventional solid-state reaction method. X-ray diffraction confirms the formation of perovskite in the BSFO phase and spinel cubic structure in the NZF phase, absent from any elemental residues. It also signifies the successful incorporation of Sm ions into the BFO lattice. The utilization of field emission scanning electron microscopy (FESEM) combined with energy dispersive X-ray spectroscopy (EDX) for microstructural analysis demonstrates densified structures resulting from reduced grain sizes with the incorporation of NZF and verifies the composition percentages in the BSFO/NZF composite ceramic. The investigation of ferroelectric materials revealed that the ceramic hysteresis loop for the conditions of x = 0.3 and x = 0.5 demonstrated the most optimal ferroelectric behavior. The dielectric constant (ε<inf>r</inf>) exhibited composition-dependent behavior, decreasing from 4895.32 to 44.64 at 1 kHz with increasing NZF content, while demonstrating consistent frequency dispersion across 1 kHz to 1 MHz. Magnetic measurements conducted via vibrating sample magnetometry revealed a substantial increase in saturation magnetization from 0.24 emu/g to 80.06 emu/g as NZF concentration increased, under a maximum applied field of 20 kOe. Enhanced magnetic properties with preserved ferroelectricity enable potential magnetoelectric device applications. This study establishes systematic composition-property relationships that offer insights for optimizing multiferroic composites in practical applications such as sensors, actuators, and data storage devices.