Microstructural changes in (K0.5Na0.5)NbO3 ceramics sintered in various atmospheres

Fisher, John G.; Kang, Suk–Joong L.

doi:10.1016/j.jeurceramsoc.2009.02.006

Cited by 95 publications

(61 citation statements)

References 38 publications

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“…Pure KNN phase can be obtained only when the calciation temperature reaches 800 °C, which is accorded with the results in [15]. It can be inferred that the activity of niobic acid obtained by the decomposition of the precursor in situ is higher than that of Nb 2 O 5 reagent.…”

Section: Methodssupporting

confidence: 88%

“…Kang et al [15] has prepared single-phase KNN using C 4 H 4 O 6 KNa·4H 2 O and Nb 2 O 5 as raw materials which were ball-milled for 24 h and then calcined at 800 °C for 5 h. In our controlled experiments, although KNN phase can be formed, small amount of Nb 2 O 5 and K 2 Nb 4 O 11 impurities appear when C 4 H 4 O 6 KNa·4H 2 ONb 2 O 5 mixture with 1:1 molar ratio are heated below 700 °C (the XRD results are not shown here). Pure KNN phase can be obtained only when the calciation temperature reaches 800 °C, which is accorded with the results in [15].…”

Section: Methodsmentioning

confidence: 99%

“…How to get stoichiometic KNN solid solution powders has been paid more attention today. KNN powders can be prepared simply by conventional solid-state synthesis route [5,[13][14][15][16][17][18][19][20][21]. However, the main disadvantages involved are (i) time-consuming ball milling process, (ii) inhomogeneous mixing, (iii) multiple calcinations at elevated temperatures (750-950 °C), (iv) volatilization of alkali oxides during sintering process and (v) large grains.…”

Section: Introductionmentioning

confidence: 99%

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Direct preparation of K_0.5Na_0.5NbO₃ powders

Jiang

Gong

et al. 2010

Cryst. Res. Technol.

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Key words K 0.5 Na 0.5 NbO 3 , solid-state method, direct preparation. K 0.5 Na 0.5 NbO 3 powders have been directly synthesized by an alternative solid-state method. Stoichimometric mixture of ammonium niobium oxalate and C 4 H 4 O 6 KNa·4H 2 O were calcined in temperature range from 500 to 800 °C for 3 h. The precursor and calcination products were characterized with respect to stoichiometry, purity, crystalline structure, particle size and powder morphology using X-ray diffraction (XRD), X-ray fluorescence (XRF) spectrometer, scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectra, thermogravimetric (TG) analysis, differential scanning calorimetry (DSC) and UV-Vis diffuse reflectance (UV-Vis) spectroscopy. XRD and XRF results reveal that stoichiometric K 0.5 Na 0.5 NbO 3 powders could be synthesized by the method. The particle size is about 68 nm for the precursor calcined at 500 °C according to XRD data, which is in good agreement with SEM data. The average band gap energy is estimated to be 3.18 eV by UV-vis diffuse reflectance spectra.

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Section: Methodssupporting

confidence: 88%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Direct preparation of K_0.5Na_0.5NbO₃ powders

Jiang

Gong

et al. 2010

Cryst. Res. Technol.

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“…8 and refs. 51,53 ) observed in KNN prepared under inert/reducing conditions can be explained by evaporation of the alkali-rich excess surface layer. Reduced atmosphere will increase the evaporation of alkali oxides, but the evaporation occurs only at higher temperatures and mainly from the external surface of the sample since most of the porosity has been removed during densification.…”

Section: Koh (Ls) = 2 K (G) + H2o (G) + ½ O2 (G)mentioning

confidence: 98%

Sintering of sub-micron K 0.5 Na 0.5 NbO 3 powders fabricated by spray pyrolysis

Haugen

Madaro

Bjørkeng

et al. 2015

Journal of the European Ceramic Society

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K0.5Na0.5NbO3 (KNN)-based ceramics are promising lead-free piezoelectrics, but processing of these materials is an ongoing challenge. Here, we present a spray pyrolysis route to highquality KNN-based powders. Fine-grained (<100 nm as-prepared, ~130 nm calcined at 800 °C) and phase-pure KNN and Li0.03K0.485Na0.485Nb0.8Ta0.2O3 (KNNLT) powders were obtained from aqueous precursor solutions. Ceramics with 95 % of theoretical density and with normalized strain of 333 pm/V were obtained by conventional sintering. The sintering of KNN remained challenging even for the fine grained powders, and the origins of these processing challenges were investigated by dilatometry and electron microscopy. Coarsening into cuboidal grains, which strongly reduced the sinterability, was observed in alkali-oxide excess KNN, caused by the formation of a liquid phase at ~650 °C. We propose that the reactivity of alkali oxide with moisture and carbon dioxide at lower temperatures cause the formation of the liquid phase at the surface even for stoichiometric KNN powders.Evaporation, mainly of potassium oxide, at high temperatures was shown to cause the formation of a Nb-rich secondary phase. The segregation of a secondary phase and inhomogeneous distribution of K/Na are discussed in relation to sintering above the solidus temperature of KNN.

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“…It has been found that the structural transition of grain boundary and related grain growth behavior of BaTiO 3 ceramics were closely related to oxygen partial pressure during sintering [21]. Fisher et al [22][23][24] found that the orthorhombic-tetragonal and tetragonal-cubic phase transitions of (K 0.5 Na 0.5 )NbO 3 ceramics became more diffuse when they had a high oxygen vacancy concentration. Zhang et al [25] found that sintering (Ba 0.95 Ca 0.05 )(Ti 0.88 Zr 0.12 )O 3 ceramics in a protective atmosphere could increase dielectric constants.…”

Section: Introductionmentioning

confidence: 99%

Microstructure, dielectric and ferroelectric properties of 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (NBTB) and 0.05BiFeO3–0.95NBTB ceramics: Effect of sintering atmosphere

Chen

Pan

Tian

et al. 2011

Journal of Alloys and Compounds

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Microstructural changes in (K0.5Na0.5)NbO3 ceramics sintered in various atmospheres

Cited by 95 publications

References 38 publications

Direct preparation of K_0.5Na_0.5NbO₃ powders

Direct preparation of K_0.5Na_0.5NbO₃ powders

Sintering of sub-micron K 0.5 Na 0.5 NbO 3 powders fabricated by spray pyrolysis

Microstructure, dielectric and ferroelectric properties of 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (NBTB) and 0.05BiFeO3–0.95NBTB ceramics: Effect of sintering atmosphere

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Microstructural changes in (K0.5Na0.5)NbO3 ceramics sintered in various atmospheres

Cited by 95 publications

References 38 publications

Direct preparation of K0.5Na0.5NbO3 powders

Direct preparation of K0.5Na0.5NbO3 powders

Sintering of sub-micron K 0.5 Na 0.5 NbO 3 powders fabricated by spray pyrolysis

Microstructure, dielectric and ferroelectric properties of 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (NBTB) and 0.05BiFeO3–0.95NBTB ceramics: Effect of sintering atmosphere

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Direct preparation of K_0.5Na_0.5NbO₃ powders

Direct preparation of K_0.5Na_0.5NbO₃ powders