Synthesis and characterization of different dopant (Ge, Nd, W)-doped ZnO nanorods and their CO2 gas sensing applications

Undoped and Germanium (Ge), Neodymium (Nd) and Tungsten (W)-doped zinc oxide (ZnO) nanorods in powder form, which are needed for many technological applications, were synthesized. The synthesis procedure was performed through the mechanochemical combustion method using oxalic acid (H2C2O4) as a fuel at 600 °C. The XRD patterns of the ZnO samples were indexed in a hexagonal crystal structure. The solubility limits of Ge, Nd and W dopants in a ZnO lattice were found to be 3, 6 and 2 mol %, respectively. The morphological properties and existence of the dopants were investigated by SEM/EDS analysis. It was determined from the SEM analysis that the lengths of the nanorods were between 1–3 μm and their diameters were in the 50–100 nm range. The electrical conductivity measurements were determined under various temperatures and an air atmosphere via the four probe method. The conductivity values were found to slightly increase with increasing concentrations of the dopants. The sensing studies of the I-phase samples to CO2 gas under air and nitrogen atmospheres were performed in a sealed test chamber and the properties were examined as conductometric. The ZnO samples with different dopants were found to be more sensitive than the undoped ZnO under an air atmosphere. The CO2 gas response of the I-phase ZnO samples was low enough to be negligible under the nitrogen atmosphere when compared to the air atmosphere.