Chemical stability of KNbO₃, NaNbO₃, and K_0.5Na_0.5NbO₃ in aqueous medium

Abstract

In recent years, potassium sodium niobate (K0.5Na0.5NbO3, KNN) has become popular and promising among perovskite lead‐free piezoceramic systems. In this study, the chemical stability of KNN powders in aqueous medium was investigated as a function of pH, time, and powder surface area. To better understand the dissolution behavior of the complex KNN stoichiometry, subconstituents such as potassium niobate (KNbO3, KN) and sodium niobate (NaNbO3, NN) were investigated separately first. Results showed that all of the cations in the structure underwent dissolution in different values. Indicating that KNN undergoes incongruent dissolution in aqueous medium, the dissolution of A site cations was higher at lower pH while the dissolution of B site cations increased at higher initial pH. The order of released cation concentrations (CA1 = K > CA2 = Na > CB = Nb) fits with inverse relationship of cation field strength (FS) order, B = Nb5+FS > A2 = Na+FS>A1 = K+FS, at pH 4, 7 and 10 for NN, KN, and KNN. Calculated diffuse layer thickness from the ICP data confirmed to outer amorphous layer in TEM image. Also, the ratio of normalized cation concentration versus surface area of powders showed that incongruent dissolution kinetic was driven by the diffusion step.

In Vitro Biocompatibility of Piezoelectric K0.5Na0.5NbO3 Thin Films on Platinized Silicon Substrates

“…The SiPt substrates, mostly comprised of Si and platinum metal, are expected to be chemically inert in the cell culture medium and to not release ions during in vitro studies. For KNN, ion release assays have been performed on powders in several studies. − , The release of K + and Na + is 1–2 orders of magnitude higher than that of Nb 5+ due to the lower ionic strength of these ions. For 0.5 wt % powder suspensions in distilled water at room temperature the K + /Na + release is 1–3 mmol L –1 .…”

“…For KNN, ion release assays have been performed on powders in several studies. − , The release of K + and Na + is 1–2 orders of magnitude higher than that of Nb 5+ due to the lower ionic strength of these ions. For 0.5 wt % powder suspensions in distilled water at room temperature the K + /Na + release is 1–3 mmol L –1 . These values are not negligible, and studies have linked the release of ions from KNN powders to a reduction in the rate of proliferation. , Although all cations in KNN (including Ca 2+ and Ti 4+ in the doped KNN composition in this work) are nontoxic in small concentrations, ,, local concentrations of leached ions can be high.…”

“…For KNN, ion release assays have been performed on powders in several studies. [21][22][23]53 The release of K + and Na + is 1−2 orders of magnitude higher than that of Nb 5+ due to the lower ionic strength of these ions. For 0.5 wt % powder suspensions in distilled water at room temperature the K + /Na + release is 1−3 mmol L −1 .…”

Activation energies for crystallization of manganese‐doped (K,Na)NbO3 thin films deposited from a chemical solution

“…8,9 It was reported that the formation enthalpies for potassium niobate and sodium niobate, respectively, are −207 and −142 kJ/mol. 20 However, no in-depth study on the activation energies for nucleation and growth has been reported for KNN thin films grown using chemical solution deposition. Thus, this work studies activation energies for perovskite transformation, nucleation, and growth from a manganese doped KNN solution modified with acetylacetone as a chelating agent.…”

“…It was reported that the formation enthalpies for potassium niobate and sodium niobate, respectively, are −207 and −142 kJ/mol 20 . However, no in‐depth study on the activation energies for nucleation and growth has been reported for KNN thin films grown using chemical solution deposition.…”