Magnetoelectric Response in Multiferroic SrFe12O19 Ceramics

We report here the realization of ferroelectricity, ferromagnetism and magnetocapacitance effect in SrFe12O19 ceramics at room temperature. The ceramics demonstrate a saturated polarization hysteresis loop, two I-V peaks and large anomaly of dielectric constant near Curie temperature. These evidences confirmed the ferroelectricity of SrFe12O19 ceramics after annealing in O2 atmosphere. The remnant polarization of the SrFe12O19 ceramic is 103 {\mu}C/cm2. The material also exhibits strong ferromagnetic characterization, the coercive field and remnant magnetic moment are 6192Oe and 35.8emu/g, respectively. Subsequent annealing SrFe12O19 ceramics in O2 not only reveals its innate ferroelectricity but also improves the ferromagnetic properties through transforming Fe2+ into Fe3+. By applying a magnetic field, the capacitance demonstrates remarkable change along with B field, the maximum relative change of dielectric constant is 1174%, which reflects a giant magnetocapacitance effect in SrFe12O19. These combined functional responses in SrFe12O19 ceramics opens substantial possibilities for applications in novel electric devices

Structural, Electrical, and Magnetic Properties of Mullite-Type Ceramic: Bi₂Fe₄O₉

This work reports the structure, electrical and magnetic properties of the orthorhombic (Pbam) structured bulk Bi2Fe4O9 synthesized by the solid-state reaction process. Bi2Fe4O9 has been studied using several experimental techniques such as X-ray diffraction, scanning electron microscopy, Raman spectroscopy, dielectric spectroscopy, and magnetometry. Rietveld-refined X-ray diffraction data and Raman spectroscopy results clearly reveal the formation of Bi2Fe4O9 perovskite structure and all the peaks of Bi2Fe4O9 perfectly indexed in the orthorhombic (Pbam) structure. It has been established that the Raman spectrum identified Ag, B2g, and B3g active optical phonon modes, and that the Raman peak at 470 cm−1 may have a magnetic origin. As a result, the coexistence of weak ferromagnetic and antiferromagnetic orders in Bi2Fe4O9 ceramic was established. The remanent magnetization (2Mr) and coercivity (2Hc) are 8.74 × 10−4 emu/g and 478.8 Oe, respectively. We report a remarkable multiferroic effects in polycrystalline Bi2Fe4O9 ceramic. These characteristics make this material very useful in technology and practical applications

Graded Interface Models for More Accurate Determination of van der Waals-London Dispersion Interactions Across Grain Boundaries

Attractive van der Waals–London dispersion interactions between two half crystals arise from local physical property gradients within the interface layer separating the crystals. Hamaker coefficients and London dispersion energies were quantitatively determined for Σ5 and near-Σ13 grain boundaries in SrTiO3 by analysis of spatially resolved valence electron energy-loss spectroscopy (VEELS) data. From the experimental data, local complex dielectric functions were determined, from which optical properties can be locally analyzed. Both local electronic structures and optical properties revealed gradients within the grain boundary cores of both investigated interfaces. The results show that even in the presence of atomically structured grain boundary cores with widths of less than 1 nm, optical properties have to be represented with gradual changes across the grain boundary structures to quantitatively reproduce accurate van der Waals–London dispersion interactions. London dispersion energies of the order of 10% of the apparent interface energies of SrTiO3 were observed, demonstrating their significance in the grain boundary formation process. The application of different models to represent optical property gradients shows that long-range van der Waals–London dispersion interactions scale significantly with local, i.e., atomic length scale property variations

Fabrication and optical properties of water soluble CdSeS nanocrystals using glycerin as stabilizing agent.

Herein we present an unusual phosphine-free method to fabricate water soluble CdSeS nanocrystals in cubic structure. In this method, glycerin was used as a stabilizing agent replacing tri-n-octylphosphine oxide (TOPO). Water solution of Na2SeO3 in polyethylene glycol was utilized as Se source. 3-Mercaptopropionic acid (MPA) provides S source. The phosphine-free Se and S sources were found to be highly reactive and suitable for the synthesis of CdSeS nanocrystals. XRD and HRTEM images confirm the formation of CdSeS nanocrystals in zinc blende structure. The absorption peaks on UV-vis spectra of as-prepared CdSeS nanocrystals are tunable from 330 nm to 440 nm, which blue shifts to shorter wavelength side in comparison with that of pure CdSe nanocrystals. The cubic CdSeS nanocrystals demonstrate narrow PL emissions spectra between 464 and 615 nm. Transmission electron microscopy images show the uniformity for the size distribution of the ternary QDs. Series water soluble CdSe(1-x)S(x) (x = 0:1) nanocrystals have also been synthesized using Na2SeO3 and Na2S solution as the Se-S co-sources. Tunable band gap energies of CdSe(1-x)S(x) (x = 0:1) nanocrystals upon chemical composition x have been achieved, the gap ranges from 290 nm to 558 nm

Facile Synthesis and Optical Properties of Small Selenium Nanocrystals and Nanorods

Abstract Selenium is an important element for human’s health, small size is very helpful for Se nanoparticles to be absorbed by human's body. Here, we present a facile approach to fabrication of small selenium nanoparticles (Nano-Se) as well as nanorods by dissolving sodium selenite (Na2SeO3) in glycerin and using glucose as the reduction agent. The as-prepared selenium nanoparticles have been characterized by X-ray diffraction (XRD), UV-Vis absorption spectroscopy and high resolution transmission electron microscope (HRTEM). The morphology of small Se nanoparticles and nanorods have been demonstrated in the TEM images. A small amount of 3-mercaptoproprionic acid (MPA) and glycerin play a key role on controlling the particle size and stabilize the dispersion of Nano-Se in the glycerin solution. In this way, we obtained very small and uniform Se nanoparticles; whose size ranges from 2 to 6 nm. This dimension is much smaller than the best value (>20 nm) ever reported in the literatures. Strong quantum confinement effect has been observed upon the size-dependent optical spectrum of these Se nanoparticles

Tunable photoluminescence spectra of CdSeS nanocrystals with particle size.

<p>CdSeS nano-specimens were heat treated at (a) 80°C, (b) 180°C, (c) 220°C, (d) 260°C, all for 5 minutes.</p

TEM and HRTEM images of as-prepared CdSe_0.2S_0.8 nanocrystals.

<p>TEM and HRTEM images of as-prepared CdSe_0.2S_0.8 nanocrystals.</p