Lead-free ferroelectrics; Cation vacancies; Laser-induced breakdown spectroscopy; Dielectric measurements;INDUCED BREAKDOWN SPECTROSCOPY; FREE PIEZOELECTRIC CERAMICS; SODIUM-POTASSIUM NIOBATE; ELECTRICAL-PROPERTIES; (K0.5NA0.5)NBO3 CERAMICS; NA0.5K0.5NBO3 CERAMICS; PHASE-TRANSITIONS; MICROSTRUCTURE; TEMPERATURE; PZT

The formation of cation vacancies can be useful for electro-chemical devices. In this regard, an understanding of vacancy formation is an important subject for enhancing current electrochemical devices and for developing next generation energy devices. In this work, we chose the well-known lead-free ferroelectric (K0.5Na0.5)NbO3 (KNN) as a model system to understand both the formation of cation vacancies and the relationship between cation vacancies and the physical properties. We studied sintering-duration dependence of the dielectric properties and the cation contents of KNN ceramics at the temperatures near the melting point of KNN. The difference in sintering duration led to a drastic change in the dielectric property, as well as to the creation of cation vacancies. Interestingly, we observed unequal evaporation of cations during the sintering process, which was confirmed by the data obtained from laser-inducedbreakdown spectroscopy. In addition, we found more drastic changes in the imaginary dielectric constant, which were likely due to a decrease in ionic conducting species, such as K and Na, in KNN.

Raman; laser-induced breakdown spectroscopy; LIBS; matrix effect; geological samples;QUANTITATIVE-ANALYSIS; SPECTROMETER; MIXTURES

Quantitative Raman analysis was carried out with geologically mixed samples that have various matrices. In order to compensate the matrix effect in Raman shift, laser-induced breakdown spectroscopy (LIBS) analysis was performed. Raman spectroscopy revealed the geological materials contained in the mixed samples. However, the analysis of a mixture containing different matrices was inaccurate due to the weak signal of the Raman shift, interference, and the strong matrix effect. On the other hand, the LIBS quantitative analysis of atomic carbon and calcium in mixed samples showed high accuracy. In the case of the calcite and gypsum mixture, the coefficient of determination of atomic carbon using LIBS was 0.99, while the signal using Raman was less than 0.9. Therefore, the geological composition of the mixed samples is first obtained using Raman and the LIBS-based quantitative analysis is then applied to the Raman outcome in order to construct highly accurate univariate calibration curves. The study also focuses on a method to overcome matrix effects through the two complementary spectroscopic techniques of Raman spectroscopy and LIBS.