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Author: search.filters.author.Bongkarn, TheerachaiSubject: search.filters.subject.C. Dielectric properties

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    Low temperature fabrication of lead-free KNN-LS-BS ceramics via the combustion method
    (2013-05-01)
    Wattanawikkam, Chakkaphan
    ;
    Vittayakorn, Naratip
    ;
    Bongkarn, Theerachai
    Lead-free piezoelectric 0.992(0.95K<inf>0.5</inf>Na<inf>0.5</inf>NbO <inf>3</inf>-0.05LiSbO<inf>3</inf>)-0.008BiScO<inf>3</inf>; KNN-LS-BS ceramics were successfully prepared using the combustion method. The highest % perovskite phase was found in the sample calcined at 700 °C for 1 h. The structural phase of orthorhombic structure was also detected in this sample. For the sintered ceramics, a pure tetragonal perovskite phase was observed in the samples sintered between 1025 and 1100 °C. The microstructure of ceramics showed a square or rectangular shape and the average grain size increased with increasing of sintering temperature. The density of the ceramics increased with increasing of sintered temperature up to 1075 °C, were it reached 97.5% of theoretical density and then dropped in value when the sintered temperature further increased. The excellent electrical properties of ε<inf>r</inf> at T<inf>c</inf>=6600, tanδ at T<inf>c</inf>=0.04, P<inf>r</inf> (at 40 kV/cm)=19.4 μC/cm<sup>2</sup> and E<inf>c</inf> (at 40 kV/cm)=24.1 kV/cm were obtained in the most dense ceramic. The results indicate that the KNN-LS-BS ceramics are promising lead-free piezoelectric materials. © 2012 Elsevier Ltd and Techna Group S.r.l.
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    Crystal structure, microstructure and electrical properties of (1-x-y)Bi0.5Na0.5TiO3-xBi0.5K 0.5TiO3-yBiFeO3 ceramics near MPB prepared via the combustion technique
    (2013-05-01)
    Sumang, Rattiphorn
    ;
    Vittayakorn, Naratip
    ;
    Bongkarn, Theerachai
    (1-x-y)Bi<inf>0.5</inf>Na<inf>0.5</inf>TiO<inf>3</inf>-xBi <inf>0.5</inf>K<inf>0.5</inf>TiO<inf>3</inf>-yBiFeO<inf>3</inf> (BNKFT-x/y with 0.12≤x≤0.24, 0≤y≤0.07) lead-free piezoelectric ceramics have been prepared by the combustion technique. The effects of amounts of x and y on structures and electrical properties were examined. Powders and ceramics can be well calcined and sintered at 750 °C for 2 h and 1025-1050 °C, respectively. The results indicated that the crystalline structure and microstructure changed with the increase of x and y concentrations. XRD results of BNKFT-x/0.03 and BNKFT-0.18/y ceramics with 0.12≤x≤0.24 and 0≤y≤0.07 showed the rhombohedral-tetragonal morphotropic phase boundary (MPB). The addition of y caused a promoted grain growth while the addition of x suppressed the grain growth. The highest density (ρ=5.85 g/cm<sup>3</sup>), superior dielectric properties at T<inf>c</inf> (ε<inf>r</inf>=7846 and tan δ=0.02), remnant polarization measured at 40 kV/cm (P<inf>r</inf> = 20.1 μC/cm<sup>2</sup>) and piezoelectric coefficient (d<inf>33</inf>=213 pC/N) were obtained for x=0.18 and y=0.03. © 2012 Elsevier Ltd and Techna Group S.r.l.
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