Thermodynamic CoO–Co₃O₄ crossover using Raman spectroscopy in magnetic octahedron‐shaped nanocrystals

Abstract

This work describes the effect of the laser power and the exposure time on a sample of octahedron‐shaped nanocrystals of cobalt(II) oxide using Raman spectroscopy. Above a certain value of the laser power and exposure time, CoO rock salt sample evolves clearly to the oxidized Co3O4 normal spinel material because of the energy transfer and consequent local heating induced by the applied laser. The analysis of this thermodynamic CoO–Co3O4 crossover in octahedron‐shaped nanocrystals by means of the Raman spectroscopy has been performed. Copyright © 2017 John Wiley & Sons, Ltd.

Raman study of Ming porcelain dark spots: Probing Mn‐rich spinels

“…This is consistent with the irreducible representation of the normal modes showing that only oxygen motions are expected for the A 1g mode . As tetrahedral and octahedral sites share oxygen, oxygen displacements and corresponding restoring forces depend on the nature of both T and M cations, even when these cations are at rest . As a matter of fact, it has been shown that both wavenumber and intensity of the A 1g mode in the Raman spectra depend on the nature of the cations, A or B, and their location on the T and/or M sites .…”

“…With respect to laser‐induced material transformation, the local temperature is definitely a key parameter. In the papers addressing the issue of laser‐induced heating we cite here, local temperatures were actually not determined . This is likely due to technical limitations of spectrometers available.…”

“…The heating of Fe 3 O 4 or MgFe 2 O 4 under air can induce phase transformation in hematite (α‐Fe 2 O 4 ) . Finally, CoO nanoparticles were shown to transform into Co 3 O 4 under laser illumination . In the case of partially inverse spinel such as CoFe 2 O 4 , heating can also have a strong impact on cation distribution between tetrahedral and octahedral sites, leading to changes in the Raman spectra .…”

Synthesis and color properties of the TiO2@CoAl2O4 blue pigments with low cobalt content applied in ceramic glaze

“…The peak located at 206 cm −1 was assigned to the lowest frequency T 2g symmetry species corresponding to the (Co, Al)‐O bending vibration (δ (Co, Al)‐O ) in the CoAl 2 O 4 phase . The broad peaks around 517 and 695 cm −1 were assigned to the F 2g and A 1g modes of the Co 3 O 4 phase . The peaks at 270 and 337 cm −1 were assigned to CoTiO 3 phase, and the peaks at 402 and 387 cm −1 were assigned to Al 2 O 3 phase.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XII

“…Rivas‐Murias and Salgueirino described a thermodynamic CoOCo 3 O 4 crossover using Raman spectroscopy in magnetic octahedron‐shaped nanocrystals. They found that above a certain value of the laser power and exposure time, CoO rock salt sample evolves clearly to the oxidized Co 3 O 4 normal spinel material because of the energy transfer and consequent local heating induced by the applied laser . Roy et al studied the charge transfer mechanism and adsorptive stance of MB on Au nanocolloids (AuNC).…”