Influence of the A/B nonstoichiometry, composition modifiers, and preparation methods on properties of Li- and Ta-modified (K,Na)NbO3 ceramics

Morozov, Maxim I.; Hoffmann, Michael J.; Benkert, Katrin; Schuh, Carsten

doi:10.1063/1.4768211

Cited by 9 publications

(12 citation statements)

References 24 publications

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“…), the formation of solid solutions, K/Na ratio, and others. In addition, other methods besides the construction of phase boundaries also affect the piezoelectricity of KNN-based materials, such as sintering temperatures, ,− reactive template grain growth, ,,− spark-plasma sintering, ,− nonstoichiometry, ,,,− two-step sintering, ,− single crystal, ,− ,− poling conditions, ,,,− sintering ai...…”

Section: Type and Construction Of Phase Boundariesmentioning

confidence: 99%

Potassium–Sodium Niobate Lead-Free Piezoelectric Materials: Past, Present, and Future of Phase Boundaries

2015

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compositions but also the temperatures, as shown in Figure 5a. Such a phase boundary is obviously different from that of PZT (see Figure 5b). Regardless of the presence of MPB or PPT characteristics, the polarization of a piezomaterial can be more easily rotated among different symmetries when the compositions are located at the phase boundaries, inducing an enhancement in dielectric and piezoelectric properties. However, recent advances indicate that there is a limited improvement in the d 33 values for KNN materials with O−T or R−O phase boundaries, 90−105,250−252 which is also inferior to most PZT ceramics 5 or even textured KNN. 12 As a result, the formation of R−T boundaries that are similar to PZT may become necessary to further enhance the piezoelectric activity of KNN, because the easy rotations of polarization axes can be induced in compositions near such a phase boundary. 11,35,70,76,106−117 In addition, we recently confirmed this assumption in potassium−sodium niobate piezoceramics by experimental methods, 106−116 and a larger d 33 value has been attained by constructing R−T phase boundaries. 106−112

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Section: Type and Construction Of Phase Boundariesmentioning

confidence: 99%

Potassium–Sodium Niobate Lead-Free Piezoelectric Materials: Past, Present, and Future of Phase Boundaries

2015

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“…At the same time, the reducing conditions will transform all manganese to Mn 2+ [33], such that leakage current mediation through Equation (4) is not possible. Mn doping might therefore expand the pO 2 region where the sample has low leakage [30,42], but is not sufficient to prevent leakage current when sintering in H 2 . The leakage current of the H 2 -sintered samples decreased upon annealing in air, confirming the n-type conductivity in reduced samples.…”

Section: Piezo-and Ferro-electric Response Of Knnltm Ceramicsmentioning

confidence: 99%

Hybrid Atmosphere Processing of Lead-Free Piezoelectric Sodium Potassium Niobate-Based Ceramics

Haugen

2019

Ceramics

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K 0.5 Na 0.5 NbO 3 -based ceramics, a promising group of lead-free piezoelectrics, are challenging to sinter dense while avoiding alkali evaporation. This work explores hybrid atmosphere processing, a new approach where reducing atmospheres is used during heating to avoid coarsening from alkali carbonates and hydroxides, and oxidizing atmospheres is used during sintering to avoid alkali evaporation. Discs of Li 0.06 (K 0.52 Na 0.48 ) 0.94 Nb 0.71 Ta 0.29 O 3 with 0.25 mol% Mn (KNNLTM) were sintered in air, N 2 , 9% H 2 in N 2 , or 9% H 2 in N 2 during heating and air during sintering (hybrid atmosphere processing). The highest density was obtained by sintering in 9% H 2 in N 2 , but resulted in high alkali loss and decomposition of the surface, followed by low piezoelectric response. However, with the hybrid H 2 /air processing it was possible to both avoid surface decomposition and leakage currently associated with alkali evaporation during sintering in H 2 , and to obtain a denser, more phase-pure and small-grained KNNLTM ceramic with a higher piezoelectric response than obtained by sintering in air or N 2 .

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“…15,[19][20][21][22] Solid state processing of KNN (especially Li and Ta codoped KNN) can also result in inhomogeneity unless a pre-reaction of the B-site oxides through the "precursor method" is performed. 23,24 Wet chemical methods generally produce homogeneous ceramic powders of small particle size with good stoichiometry control. KNN-based powders have been prepared by hydrothermal, 25,26 spray drying 27,28 and sol-gel 22,29,30 syntheses among others, and high density and excellent piezoelectric properties have been obtained.…”

Section: Introductionmentioning

confidence: 99%

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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Influence of the A/B nonstoichiometry, composition modifiers, and preparation methods on properties of Li- and Ta-modified (K,Na)NbO3 ceramics

Cited by 9 publications

References 24 publications

Potassium–Sodium Niobate Lead-Free Piezoelectric Materials: Past, Present, and Future of Phase Boundaries

Potassium–Sodium Niobate Lead-Free Piezoelectric Materials: Past, Present, and Future of Phase Boundaries

Hybrid Atmosphere Processing of Lead-Free Piezoelectric Sodium Potassium Niobate-Based Ceramics

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

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