Slobodna trgovina važan je čimbenik gospodarskog razvoja i stvaranja novih radnih mjesta. Transatlantski odnosi i trgovina imaju globalni utjecaj, a njihovo je značenje osobito poraslo nakon ...osnivanja Europske zajednice. Europska unija (EU) i Sjedinjene Američke Države (SAD) prolazile su kroz različite faze i modele razvoja tijekom posljednjeg stoljeća, a što je obilježilo odnose međusobne suradnje. Cilj rada je dati pregled ključnih značajki novog Transatlantskog sporazuma o trgovini i investicijama (TTIP) i očekivanih utjecaja potpisivanja istoga na zemlje članice te na treće zemlje. Očekivani efekti nisu jednoznačni niti jednako raspoređeni među zemljama, a ovisit će o vrsti dobara koja se razmjenjuju između zemalja članica i s trećim zemljama, o divergenciji u propisima te o obuhvatu samog sporazuma. Može se također utvrditi da efekti od ukidanja carinskih prepreka neće biti toliko značajni koliko će to biti efekti od usklađivanja i ukidanja necarinskih prepreka trgovini i ulaganjima.
Cold sintering is an attractive method for sintering ferroelectric ceramics at temperatures at or below 300 °C. While we can practically obtain bulk samples by introducing a transient liquid and ...applied pressure, the mechanisms of sintering and final functional properties of cold-sintered ceramics are far from being understood. Here, we investigate the influence of grain size and sintering parameters on the microstructure and ferroelectric properties of 0.5 % Sr-doped K0.5Na0.5NbO3 ceramics. By comparing with the conventionally-sintered samples, we find that cold-sintered ceramics have higher dielectric permittivity and lower dielectric losses, which we attribute to smaller grains and higher relative density. Using atomic-scale analysis, we point out the presence of numerous lattice dislocations that likely act as pinning sites and thus inhibit any significant polarization-switching behaviour. Due to the slim P–E loop and high dielectric breakdown fields of the cold-sintered ceramics we consider its potential for energy storage applications.
This study was designed to better understand the microstructural and phase evolution of lead-free sodium potassium niobate based piezoceramics with a nominal composition (K0.5Na0.5)0.99Sr0.005NbO3 ...(KNNSr) during pressure-less spark plasma sintering followed by post-annealing in oxygen. The as-sintered samples were dark-coloured and electrically conductive as a result of partial reduction of Nb5+ to Nb4+ and formation of oxygen vacancies confirmed by X-ray photoelectron and Raman spectroscopy. The Rietveld refinement analysis showed that the as-sintered samples contained two perovskite phases with monoclinic Pm unit cell and slightly different unit-cell parameters. The microstructure with sub-micrometre-sized grains unambiguously confirmed that rapid heating and short dwell time hindered the grain growth. We found that post-annealing the samples at 950 °C in oxygen led to improvement in functional properties. The samples became white-coloured, the both perovskite unit cells decreased as a result of re-oxidation, while the microstructure remained essentially unchanged. The KNNSr sintered at nominal sintering temperature of 1300 °C for 3 min and post-annealed possessed a relative density of 88% and dielectric and piezoelectric properties similar to those of the conventionally sintered samples. Our findings contribute to the understanding of pressure-less spark plasma sintering of sodium potassium niobate-based materials and suggest that arrested grain growth and minimisation of alkali evaporation not necessarily lead to dense ceramic.
