Effect of quenching technique on electrical properties of KNN ceramics

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dc.contributor.authorSompong, Khanisorn
dc.contributor.authorKaewsit, Sriwan
dc.contributor.authorParjansri, Piewpan
dc.contributor.authorPengpat, Kamonpan
dc.contributor.authorYongsiri, Ploypailin
dc.date.accessioned2026-08-06T10:55:28Z
dc.date.available2026-08-06T10:55:28Z
dc.date.issued2026-05-01
dc.description.abstractCooling 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.
dc.identifier.citationCeramics International, 52(12), 19379-19391, 2026
dc.identifier.doi10.1016/j.ceramint.2026.03.035
dc.identifier.issn02728842
dc.identifier.other2-s2.0-105033382759
dc.identifier.urihttps://dspace.kmitl.ac.th/handle/123456789/18083
dc.sourceCeramics International
dc.subjectDielectric properties
dc.subjectFerroelectric properties
dc.subjectKNN
dc.subjectQuenched
dc.subjectSintering
dc.titleEffect of quenching technique on electrical properties of KNN ceramics
dc.typeArticle

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