Thermal study on the synthesis of the doped ZnO to be used in TCO films

ZnO, Li doped, and Li, Ni co-doped ZnO powders to be later used as transparent conductive oxide thin film were prepared by heat treatment of gels obtained from alcoholic Zn(CH3COO)(2)center dot 2H(2)O, LiNO3 center dot nH(2)O and NiSO4 center dot 6H(2)O solutions with (CH3CH2OH)(3)N as chelating agent. The properties of the powders and their thermal treatment were studied by thermogravimetric and differential thermal analysis (TG/DTA), differential scanning calorimetry, evolved gas analysis coupled with mass spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray. The as-prepared gels consisted of submicron platelet-like particles and contained zinc acetate dihydrate and hydrozincite in different amount and with different preferred orientations. During annealing of the gels, zinc acetate decomposed between 110 and 350 A degrees C with the release of CH3COOH, acetone and CO2. The N content of the chelating agent was responsible for NH3 and NO evolution. The thermal behavior of the doped gels was similar, but there were also differences in the mass losses, amount of released gases. Based on TG/DTA data, ZnO powders were obtained from the gels by annealing both at 275 and 500 A degrees C. After heating at 275 A degrees C, the obtained powders consisted of spherical 1-2 micron grains of wurtzite. The inclusion of the dopants was successful according to EDX and cell parameter data. Thermal study of the powder annealed at 275 A degrees C confirmed that they still contain some zinc acetate. In the case of the doped samples, the mass loss was smaller, since the Li and Ni dopants catalyzed the composition of zinc acetate during the previous annealing at 275 A degrees C. After annealing the gels at 500 A degrees C, stable undoped ZnO or doped ZnO particles were obtained.