Materials Science Aspects Relevant for High‐Temperature Electrochemistry

Eriksson, Annika K.; Einarsrud, Mari‐Ann; Grande, Tor

doi:10.1002/9783527635566.ch9

Cited by 2 publications

(1 citation statement)

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“…Thermodynamically one can argue that compounds with basic oxides such as alkali or alkali earth oxides will react with H2O and CO2 at ambient conditions. This is a well-known problem with the stability of proton conductor such as Ba(Ce,Zr)O3 41 or similar Sr compounds. Possible reactions, exemplified with KNbO3 instead of KNN, are shown in Eqs.…”

Section: Discussionmentioning

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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Section: Discussionmentioning

confidence: 99%