RESUMO
We report a comprehensive comparative study of ferroelectric and piezoelectric properties of BNT-BKT-BT ceramics through the MPB (morphotropic phase boundary) zone, from the rhombohedral to the tetragonal phases in the system (97.5-x)(Bi0.5Na0.5)TiO3 + x(Bi0.5K0.5)TiO3 + 2.5(BaTiO3), where x = 0 to 24.5 mol %. The structural transitions were studied by XRD patterns and Raman spectra. The MPB was confirmed between x = 10 and 12.5 mol % BKT. The dielectric/ferroelectric/piezoelectric properties of the BNT-BKT-BT system are maximized in the MPB region exhibiting a dielectric constant of 1506, a remanent polarization of 34.4 µC/cm², a coercive field = 36.9 kV/cm, and piezoelectric values of d33 = 109 pC/N, kt = 0.52, and kp = 0.24. Changes in microstructure as a function of BKT content are also presented and discussed.
RESUMO
Rice husk was employed as a source for producing silica micro- and nanoparticles through its digestion by soil fauna. Although many physicochemical methods for producing nanostructures have been studied, the biological processes remain mostly unexplored. Alkaline hydrogen peroxide with continuous control of reaction pH allowed removal of lignin bonds while preserving most of the cell wall and the silica present in the rice husk. The accessibility of lignocellulose was achieved without removing appreciable amounts of lignin, so this agricultural byproduct can be employed as feeding material for microarthropods Folsomia candida (Collembola). When these microarthropods are placed on a substrate of treated rice husk, more than 85% of degraded material is obtained, as compared to the untreated rice husk substrate, while the silica particles obtained show a slight decrease in average size.
