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.

AEROSOL-PARTICLES; AIR-POLLUTION; METALS; FINE

A laser-induced breakdown spectrometer (LIBS) was developed for determining the elemental composition of individual airborne particles. The system employs two lasers focused on a narrow beam of particles. A continuous wave laser placed upstream scatters light from particles, while a pulse laserdownstream ablates the particles. The scattered light from the upstream laser is used to trigger the downstream pulse laser, resulting in more accurate hitting of the particles than a free-firing laser system without the triggering signal (i.e., constant pulse laser firing). Various laboratory-generated aerosols (NaCl, MgCl2, KCl, and CaCl2) were used to evaluate the newly developed LIBS system. Particles were tightly focused into a center line with a sheath air focusing system using an optimum aerosol-to-sheath air velocity ratio. The locations of both the scattering laser and pulse laser beams were precisely controlled by a motorized X-Y stage controller. Data showed that for the LIBS with the triggering system, the hitting efficiency (%) of particles (200-600 nm) significantly increased (e.g., 350 nm particles had more than 26 times higher hitting efficiency at 1,000 particles/cm(3)), and much lower limits of particle size (similar to 200 nm) and number concentration (<100 particles/cm(3)) were achieved compared to the free-firing laser condition. Additionally, the hitting rate (hits/min) significantly increased with the triggering system. Our results suggest that the LIBS with the triggering system can be useful for real-time detection of elements of particles existing at low number concentrations (e.g., atmospheric particles) and for the determination of the variation of elemental composition among particles.