RESUMO
Aurivillius phase Bi2LaNb1.5Mn0.5O9, derived from ferroelectric PbBi2Nb2O9 by simultaneous substitution of the A-site and B-site cations, was synthesized using a molten-salt method. Here, we discuss the structure-property relationships in detail. X-ray and neutron diffraction show that Bi2LaNb1.5Mn0.5O9 adopts an A21am orthorhombic crystal structure. Rietveld refinement analysis, supported by Raman spectroscopy, indicates that the Bi3+ ions occupy the bismuth oxide blocks, La3+ ions occupy the perovskite A-site, and Nb5+/Mn3+ ions occupy the perovskite B-site. Ferroelectric ordering takes place at 535 K, which coexists with local ferromagnetic order below 65 K. The cation disorder on the B-site results in relaxor-ferroelectric behavior, and the short-range ferromagnetic order can be attributed to Mn3+/Mn4+ double-exchange. Magnetodielectric coupling measured at 5 K and 100 kHz in a field of 5 T suggests the existence of intrinsic spin-lattice coupling with a magnetodielectric coefficient of 0.20%. These findings will provide significant impetus for further research into potential devices based on the magnetodielectric effect in Aurivillius materials.
RESUMO
Background: Most natural plants used in the synthesis of silver nanoparticles are limited to marine plants. To carry out applications, colloidal silver nanoparticles (AgNps) should have appropriate properties such as homogeneous shapes, small and narrow particle size distribution, and long time stability. This study aims to determine the effects of a variable process of AgNps mediated mangrove Rhizophora stylosa (RS) leaf extract, and antibacterial activity. Methods: Synthesis of AgNps was carried out by stirring silver nitrate solution with aqueous extract. The characterization of AgNps was carried out using UV-Vis spectrophotometry, X-ray diffraction (XRD), Dynamic Light Scattering (DLS) zetasizer and Transmission Electron Microscopy (TEM). Evaluation of antibacterial activity was carried out on E scherichia coli and Staphylococcus aureus. Reaction conditions such as the concentration of metal ions (0.001 M, 0.005 M, and 0.01 M), extracts (1%, 3%, and 5% v/v), and the reaction time on the size and stability of nanoparticles were also explored. Results: The UV-Vis spectroscopy showed an absorption of colloidal AgNps in a wavelength range of 403-443 nm. TEM analysis showed that as-synthesized AgNps were spherical in shape with a size range of 5-87 nm. The use of 0.001 M and 0.005 M of Ag + resulted in a smaller diameter than the synthesized AgNps, using 0.01 M Ag +, in the same extract concentration. The range of zeta potential was -24.9 mV to -27.7 mV. The as-synthesized AgNps were stable for more than one month. The XRD analysis showed four peaks, which were attributed to the face centered cubic crystal structure of metallic silver. The results of the silver nanoparticles synthesis showed good activity on E scherichia coli and Staphylococcus aureus, with an inhibition zone between 4.1-7.2 mm. Conclusions: The AgNps synthesized with RS leaf extract, which is a reducing agent, showed good potential as an antibacterial component.
