Determining the stoichiometry of (K,Na)NbO(3) using optimized energy-dispersive x-ray spectroscopy and electron energy-loss spectroscopy analyses in a transmission electron microscope

Official URL: http://dx.doi.org/10.1111/j.1551-2916.2011.04389.x

This paper describes an optimized analytical procedure for determining the composition of alkaline niobate-based lead-free piezoceramics by energy-dispersive X-ray spectroscopy (EDXS) in a transmission electron microscope (TEM). To discriminate the material-specific composition from the artifacts introduced during the EDXS/TEM analyses, the effects of radiation damage and the absorption of the characteristic X-ray lines were studied in detail. The optimized, quantitative EDXS analysis was tested on sodium potassium niobate with the nominal composition K(0.5)Na(0.5)NbO(3) (KNN) by applying KNbO(3) and NaNbO(3) as standards. The results obtained indicate that KNbO(3) is more radiation sensitive than NaNbO(3). A similar degradation was confirmed in KNN, where the loss of potassium was higher than that of sodium. In addition, the degradation of the KNN was associated with a severe oxygen loss and the reduction of niobium. To achieve highly reliable, quantitative analyses and to preserve good counting statistics, the optimum conditions for the EDXS/TEM analyses were found at an electron dose rate of 0.4 pA/nm(2) and an acquisition time of around 200 s in the specimen thickness range between 30 and 200 nm.