_applied sciences_  
_Article_  
Revisiting the Decomposition Process of Tetrahydrate Co(II)  
Acetate: A Sample's Journey through Temperature  
[PERSON] 1\({}^{\copyright}\), [PERSON] 1, [PERSON] 1,2, [PERSON] 3,+(c)  
and [PERSON] 1,*  
Footnote 1: email: [EMAIL_ADDRESS]  
Footnote 2: email: [EMAIL_ADDRESS]  
Footnote 3: email: [EMAIL_ADDRESS]  
Footnote 4: email: [EMAIL_ADDRESS]  
Footnote 5: email: [EMAIL_ADDRESS]  
Footnote 6: email: daniel.gutier  
wurtzite-CoO nucleates from zinc-blende crystallites, so the stabilized final phase depends on the Zn-blende particle size [15]. If the primary nuclei are small, the energy barrier for wurtzite formation can be overcome, thus enabling wurtzite formation. However, if said nuclei are large, the energy barrier is too high to allow for wurtzite formation, hence yielding Zn-blende CoO as the final product.  
The growing interest in the physical properties of nanoparticles has driven the development of preparative methods. Among the different synthetic methods, the thermal decomposition of single-source precursors is a simple way to obtain metal oxides. Cobalt hydroxide [16], cobalt nitrate [17], cobalt carbonate [18], and cobalt oxyhydroxide [19] have proven to be effective solid precursors to obtain nanostructured Co\({}_{3}\)O\({}_{4}\).  
The three CoO polymorphs can also be obtained with the same synthetic procedure. The synthesis of CoO nanoparticles from Co (II) acetylacetonate as a single precursor in oleylamine was found to result in wurtzite and Zn-blende CoO [20]. Nanocrystals of wurtzite-CoO were isolated for the first time from the thermolytic decomposition of cobalt acetylacetonate in a high-temperature solvent (benzyl ether) [21]. By using the same precursor, [PERSON] et al. analyzed some of the parameters that determine the formation of wurtzite or Zn-blende polymorphs; they also performed a detailed magnetic characterization of both CoO nanoparticles [5; 22].  
In the early works on the synthesis of these oxides, all of them (Co\({}_{3}\)O\({}_{4}\) and the three CoO polymorphs) were synthetized through the controlled thermal decomposition of cobalt (II) acetate tetrahydrate following the complementary use of diffraction and thermogravimetric techniques [15; 23; 24]. According to these results, this process goes through two main stages. At 150 \({}^{\circ}\)C, the dehydration of the starting acetate is complete, and a crystalline anhydrous acetate is stabilized at 200 \({}^{\circ}\)C. In the second step (275-310 \({}^{\circ}\)C), this new phase decomposes, giving rise to Zn-blende CoO, which transforms at 310 \({}^{\circ}\)C to a rocksalt polymorph. In any step of this process, wurtzite-CoO can be stabilized [24], although both polymorphs were present in samples prepared at 290 \({}^{\circ}\)C in argon [15]. In a later work, [PERSON] et al., [25] described the formation of a basic cobalt acetate as an intermediate product in this thermal decomposition process.  
In this work, we revisited the thermal decomposition process of Co(CH\({}_{3}\)COO)\({}_{2}\)-4H\({}_{2}\)O. The thermal decomposition of a precursor material has some advantages over other preparation methods including its simplicity, low cost, and ease of obtaining high-purity products. SEM and TEM were used to study the morphology and microstructure of the final oxides. In addition, we isolated the previously detected intermediate crystalline phase that corresponds to a Co(II) oxyacetate of chemical composition Co\({}_{3}\)O(CH\({}_{3}\)COO)\({}_{4}\).