Are organic templates responsible for the optical and magnetic response of MgO nanoparticles?

Singh, Jitendra PalKim, So HeeKang, Hee KyoungWon, Sung OkLee, Ik-JaeChae, Keun Hwa
Issue Date
Materials Chemistry Frontiers, v.2, no.9, pp.1707 - 1715
Herein, we report the optical and magnetic response of magnesium oxide nanoparticles synthesized using magnesium nitrate in a citric acid host. The precursor obtained during the synthesis process was annealed at 350 degrees C, 400 degrees C, 500 degrees C, 700 degrees C, 900 degrees C and 1100 degrees C to obtain magnesium oxide nanoparticles. The rock salt phase of the synthesized nanoparticles was investigated by Rietveld analysis of their X-ray diffraction (XRD) patterns. The temperature-dependent XRD investigation revealed a stable rock salt phase at the measured temperature of 300 degrees C for these nanoparticles. The nanoparticles exhibited varying crystallite sizes in the range from 6.9 +/- 0.2 nm to 29.7 +/- 3.9 nm as the annealing temperature increased from 350 degrees C to 1100 degrees C. Furthermore, scanning electron microscopy and transmission electron microscopy revealed the formation of regular particles above 500 degrees C; however, below this temperature, the particles appeared to be embedded in a carbonaceous-like matrix. A variation in color with annealing temperature was visually observed for the nanoparticles, which was associated with the presence of the carbonaceous-like matrix. Near-edge X-ray absorption spectroscopy (NEXAFS) measurements carried out at the O K-edge also revealed a carbonaceous-like matrix, and these results were supported by C and N K-edge measurements. These measurements indicated the presence of C-O-, C?O-, C-N-, and C-H-like bonds attached to MgO crystallites having dominant contribution at low annealing temperatures. This behavior was also reflected by the X-ray photoelectron spectroscopic measurements at O 1s, C 1s and N 1s. The Mg K-edge NEXAFS measurements exhibited slight distortion in the Mg2+ ion coordination at lower annealing temperatures, which may be due to the presence of Mg2+ ions in MgO- and MgCO3-like co-ordinations, as investigated from Mg 1s spectra of these nanoparticles. Diffuse reflectance measurements showed almost 100% reflectance for the nanoparticles at an annealing temperature of 900 degrees C and wavelength of 600 nm; the reflectance of these nanoparticles reduced when the annealing temperature was lowered, and it reduced to almost 8% at an annealing temperature of 350 degrees C. Additionally, O K-edge X-ray magnetic circular dichroism (XMCD) measurements obtained for these materials showed the onset of magnetism in these C-rich materials.
THIN-FILMS; SURFACE; XPS; BEHAVIOR; SPECTROSCOPY; organic templates; the optical and magnetic response; MgO nanoparticles
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KIST Article > 2018
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