CdCO3 nanocrystalline thin film grown by chemical bath and its transition to porous CdO by thermal annealing treatment

CdCO3→CdO transitions by thermal treatment (TT) at ∼400 °C in an air atmosphere are reported. The CdCO3 was grown at room temperature by using the green chemical bath (CB) approach, and the morphological, structural and optical analysis. Thus, the morphological analysis performed by SEM in CdCO3 showed crystals with a cubic geometry, long linear stacks, as well as circular regions. After TT, the morphology is retained and the sample exhibited a spongy appearance, the typical morphology of TT materials. FTIR spectra revealed absorption bands associated with CO32- and OH− ions, which disappeared after TT. XRD showed a crystalline phase of CdCO3 with rhombohedral structure, and after the CdCO3→CdO transition, CdO was identified in the cubic zincblende phase. The OA studies showed a running in the band gap from ∼4.1 eV for CdCO3 to ∼2.3 eV for CdO. A brief mechanism by calculating the Gibbs free energy changes is shown.