## 3 Results
### Thermal Decomposition under Nitrogen Atmosphere  
Figure 1a shows the XRD pattern of the commercial starting material. The whole pattern corresponds to Co(CH\({}_{3}\)COO)\({}_{2}\)-4H\({}_{2}\)O (PDF 00-025-0372), although a small intensity extra peak can be appreciated at 20 = 10.3\({}^{\circ}\). This could correspond to the most intense reflection (hkl) of the Co (II) acetate dihydrate that may have been present in the commercial product in a low ratio. The intensity of this reflection seemed to increase after the sample grinding process (Figure 1b). Figure 2 shows the TG curve for cobalt (II) acetate tetrahydrate under an N\({}_{2}\) atmosphere. Under the experimental conditions described in the previous section, the decomposition process of the Co(CH\({}_{3}\)COO)\({}_{2}\)-4H\({}_{2}\)O starting material took place through three stages labeled as A, B, and C in the figure. To identify the intermediate products formed during this process, an in situ thermodiffraction study was performed. This experiment consisted of a temperature sweep under N\({}_{2}\) every 10 \({}^{\circ}\)C from room temperature up to 400 \({}^{\circ}\)C and then down to 270 \({}^{\circ}\)C. Temperature ramps of 10 \({}^{\circ}\)C/min were used for increasing or decreasing the temperature between steps, and the temperature was kept constant during the X-ray diffraction scans. Figure 3 shows a 2D contour plot depicting the thermal evolution of the X-ray diffraction (XRD) maxima of the different products involved in this decomposition process. This type of plot enables one to easily observe the decomposition of a phase or the emergence of a new one and thus select the most suitable temperatures to collect X-ray data throughout the decomposition process. The experimental weight loss of the first step (from RT up to 110 \({}^{\circ}\)C), \(\Delta\)W = 30.4%, was close to that corresponding to the total dehydration of the starting sample (\(-\)4 H\({}_{2}\)O/mol: \(\Delta\)W = 28.9%). The slight slope change observed at 75 \({}^{\circ}\)C could indicate a different rate in the release of water molecules. According to Figure 3, the starting Co(CH\({}_{3}\)COO)\({}_{2}\)-4H\({}_{2}\)O stayed up to 70 \({}^{\circ}\)C, when its characteristic XRD lines were no longer visible. Note that the line corresponding to the most intense reflection of Co(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O (20 \(\approx\) 10\({}^{\circ}\)) remains visible after the full transformation of the tetrahydrate form (70 \({}^{\circ}\)C scan), and its intensity even slightly increases. By the 80 \({}^{\circ}\)C scan, as the water was lost, the diffraction maxima intensity of the hydrated acetates decreased and no crystalline phase emerged, although a broad maximum can be observed at 20 \(\approx\) 9\({}^{\circ}\). These features are better observed in the XRD patterns collected at RT, 60, 70, and 90 \({}^{\circ}\)C (Figure 4a-d). As can be seen in the TGA plot, the dehydration process was completed at 110 \({}^{\circ}\)C and the weight remained almost constant up to 200 \({}^{\circ}\)C.  
Figure 1: X-ray powder diffractograms of commercial cobalt acetate tetrahydrate before (**a**) and (**b**) after grinding. The most intense reflection of the dihydrated cobalt acetate (marked with an asterisk in the figures) is visible in both diagrams, although its intensity is clearly increased in the ground sample. An enlargement of both diffraction patterns is shown at the inset. Figure 2: (**a**) TGA plot of the decomposition of commercial Co(CH\({}_{3}\)COO)\({}_{2}\cdot\)4H\({}_{2}\)O under N\({}_{2}\) atmosphere. Step **A**: from RT up to 110 \({}^{\circ}\)C; Step **B**: from 110 to 275 \({}^{\circ}\)C; Step **C**: from 275 to 400 \({}^{\circ}\)C. (**b**) XRD pattern of the final product of the TGA analysis. All the intense maxima correspond to the CoO rocksalt (PDF 00-048-1719). It is not easy to determine which intermediate compounds were formed in this temperature range.