Abstract:

Polycrystalline NaCo₂O_4-δ materials were prepared using the urea auto-combustion method. The reaction process and crystal growth were investigated through X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), and Fourier transform infrared spectrometry (FTIR). The results indicate that the formation temperature of NaCo₂O_4-δ is about 620°C, which is lower than that for solid-state reaction. XRD results show that the texturing along c-axis occurred as the powders calcined at 700°C were pressed into pellets with subsequently sintering, and the degree of such texturing increases  with increasing sintering temperature. Surface morphologies by scanning electron microscopy (SEM) also indicate that the texturing show dependence on sintering temperature. The grains on the surfaces of the pellets sintered at 750 and 850°C have some growth trend along a-b planes, while the grains on the surface of the pellet sintered at 950°C show an obvious growth trend toward c-axis.

Key words: Crystal growth, Heat treatment, Sintering, Surfaces, X-ray techniques , Heat treatment , Sintering , Surfaces , X-ray techniques