Tailoring of crystal phase and Néel temperature of cobalt monoxides nanocrystals with synthetic approach conditions

Abstract

Cobalt monoxide (CoO) nanocrystals were synthesized by thermal decomposition of cobalt oleate precursor in a high boiling point organic solvent 1-octadecene. The X-ray diffraction pattern and transmission electron microscopy studies suggest that pure face-centered-cubic (fcc) phase of CoO can be synthesized in the temperature range of 569–575 K. Thermolysis product at higher synthesis temperature 585 K is a mixture of fcc and hexagonal-closed-packed (hcp) phases. These nanocrystals are single crystals of CoO and exhibit mixture of two types of morphologies; one is nearly spherical with 5–25 nm diameter, and other one is 5–10 nm thick flake. The pure fcc-CoO nanocrystals show enhanced, and mixture of fcc- and hcp-CoO nanocrystals show reduced antiferromagnetic ordering temperature. Such results provide new opportunities for optimizing and enhancing the properties and performance of cobalt oxide nanomaterials.

Hierarchical Polyelemental Nanoparticles as Bifunctional Catalysts for Oxygen Evolution and Reduction Reactions

“…[14] Raman spectroscopy was further applied to verify the lattice vibration from the transition metal oxide. As indicated in Figure 3b, the characteristic Raman peaks of FeO (A 1g at 323.3 cm -1 ), [35] CoO (E g at 479.1 cm -1 , F 2g at 622.5 cm -1 , and A 1g at 691.6 cm -1 ), [36] Co 3 O 4 (A 1g at ~661.1 cm -1 ), [37] and NiO (one-photon vibration at ~567.6 cm -1 ) [38] further indicate the formation of mixed transmission metal oxides.…”

Zinc blende and wurtzite CoO polymorph nanoparticles: Rational synthesis and commensurate and incommensurate magnetic order

“…Namely, although the decomposition of cobalt precursors often leads to a zinc blende intermediate (which is the least stable polymorph) [25], if the synthesis follows a thermodynamic regime the most stable structure, i.e., rock salt CoO, is formed ( Figure 1a). For example, thermal decomposition carried out at moderate temperatures for the synthetic approach (i.e., around 200 0 C) is enough to promote the formation of single rock salt CoO nanoparticles [26]. However, under kinetic conditions, set by the chemical parameters (precursor concentration, solvents or surfactants) and the reaction conditions (heating rate, stabilization temperature, reflux temperature or time), it is possible to form and stabilize the two other metastable polymorph CoO phases: hexagonal wurtzite and cubic zinc blende (Figure 1b,c) [25].…”

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

“…Although Raman is a non‐destructible technique, in the case of the face‐centered cubic (fcc) cobalt(II) oxide (CoO), discrepancies in Raman spectroscopy analysis have been reported . These discrepancies can stem from the difficulty in the assignments of the registered Raman bands, for example, due to the ease of this material to be transformed in the oxidized Co 3 O 4 , with spinel crystalline structure, and induced by the Raman laser power itself …”