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Effect of quenching technique on electrical properties of KNN ceramics
(2026-05-01)
Sompong, Khanisorn
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Kaewsit, Sriwan
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Parjansri, Piewpan
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Pengpat, Kamonpan
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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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Interlayer alkali ion governs robustness, reactivity, and dielectric properties of sintered lepidocrocite titanate
(2022-01-01)
Maluangnont, Tosapol
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Pulphol, Phieraya
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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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Giant suppression of dielectric loss in BaZrO3
(2019-11-01)
Kolodiazhnyi, T.
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Pulphol, P.
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Vittayakorn, W.
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Vittayakorn, N.
We report the effect of precursor's purity and heterovalent substitution on the microstructure and dielectric properties of BaZrO<inf>3</inf> ceramics. We find that independent of the purity or raw materials, the dielectric loss of BaZrO<inf>3</inf> at microwave frequencies is rather high with a Q factor in the range of 1000–3000 at 10 GHz. All stoichiometric ceramics studied show up to three types of low-T dielectric relaxations in the 2–250 K range. All these dielectric anomalies can be suppressed by partial substitution of Zr for Nb. By alloying of BaZrO<inf>3</inf> with a hypothetical BaGa<inf>1/2</inf>Nb<inf>1/2</inf>O<inf>3</inf> phase the Q × f value of ceramics at microwave frequency can be improved significantly. The origin of this remarkable improvement is attributed to the effect of the donor ions on the random electric fields and antiferrodistortive instability. Ceramic with a chemical composition of BaZr<inf>0.96</inf>Ga<inf>0.02</inf>Nb<inf>0.02</inf>O<inf>3</inf> sintered at 1600 °C shows dielectric constant, ε′ = 36.7, temperature coefficient of the resonance frequency, τ<inf>f</inf> = +110 ppm/°C and Q × f = 172 THz.
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Relationship between Atmospheric Dew Point and Sinterability of Al-Si Based Alloy
(2013-01-01)
Manonukul, A.
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Salee, A.
Al-Si based alloys are interestingly used to produce automotive components. Fabrication of such components by powder metallurgy (PM) has been developed continuously. During PM, several parameters affect the sinterability of the aluminium powder, including atmospheric dew point which is regarded as one of the crucial parameters. The objective of this work was to investigate the effect of the atmospheric dew point on the sinterability of Al-14.9Si-2.4Cu-0.55Mg by studying the sintering characters obtained under various atmospheric dew points. The aluminium alloy powder was pressed into tensile specimens and subsequently sintered in a nitrogen atmosphere at 560 °C for 60 min with varied atmospheric dew points. The results show that as the dew point decreased, the sintered properties were improved. The atmospheric dew point of -38.4 °C is sufficient to obtain good sintering characters and it is achievable in a commercial furnace. © 2013.
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Synthesis and properties of Pb(Co1/3Nb2/3)O3 ceramics
(2008-10-20)
Unruan, Muangjai
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Vittayakorn, Naratip
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Wongmaneeruang, Rewadee
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Prasatkhetragarn, Anurak
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Ananta, Supon
In this study, Pb(Co<inf>1/3</inf>Nb<inf>2/3</inf>)O<inf>3</inf> or PCN ceramics have been produced by sintering PCN powders synthesized from lead oxide (PbO) and cobalt niobate (CoNb<inf>2</inf>O<inf>6</inf>) with an effective method developed for minimizing the level of PbO loss during sintering. Attention has been focused on relationships between sintering conditions, phase formation, density, microstructural development, dielectric and ferroelectric properties of the sintered ceramics. The densities of sintered PCN ceramics increased with increasing sintering temperature. However, it was observed that at too high temperature the density began to decrease. Change of dielectric properties with sintering temperature also followed the same trend as the density. Based on X-ray diffraction analysis, density data, SEM micrograph, and dielectric properties, the optimum sintering temperature for a high purity PCN ceramic was found to be about 1100 and 1150 °C. A strongly diffused dielectric peak also showed a typical characteristic of ferroelectric relaxors. The P-E hysteresis loops observed at -70 °C were of slim-loop type with small remnant polarization values, which confirmed relaxor ferroelectric behavior of PCN ceramics. © 2007 Elsevier B.V. All rights reserved.
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Phase and morphology investigation of BaxSr1-xTiO3 (x = 0.6, 0.7 and 0.8) powders
(2006-06-01)
Kongtaweelert, S.
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Sinclair, D. C.
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Panichphant, S.
This study aims to understand thoroughly the effects of calcining and sintering conditions on the relative permittivity and sintering behaviors of the solid solution method of preparing BSTs. BST (Ba<inf>x</inf>Sr<inf>1-x</inf>TiO<inf>3</inf>, x = 0.6, 0.7 and 0.8) was synthesized using an established solid-state reaction method [R.K. Roeder, E.B. Slamovich, Stoichiometry control and phase selection in hydrothermally derived Ba<inf>x</inf>Sr<inf>1-x</inf>TiO<inf>3</inf> powders, J. Am. Ceram. Soc. 82 (7) (1999) 1655, R. Ganesh, E. Goo, Microstructure and dielectric characteristics of Pb<inf>x</inf>Ba<inf>0.5-x</inf>Sr<inf>0.5</inf>TiO<inf>3</inf> ceramics, J. Am. Ceram. Soc. 79 (1996) 225, J.W. Liou, B.S. Chiou, Effect of direct-current biasing on the dielectric properties of barium strontium titanate, J. Am. Ceram. Soc. 80 (12) (1997) 3093, T. Noh, S. Kim, C. Lee, Chemical preparation of barium-strontium titanate, Bull. Korean. Chem. Soc. 16 (1995) 1180]. BaTiO<inf>3</inf> and SrTiO<inf>3</inf> powders were used as starting materials. Crystallinity and lattice parameter of the calcined powders was improved by increasing the calcining temperature, as indicated by the increase in intensity of the X-ray diffraction peak. The particle size distribution also increasing at higher calcining temperature. The composition investigated here display dielectric properties characteristic of normal ferroelectrics. © 2005.

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