Effect of Sintering Temperature on the Texturing Behavior of NaCo2O4-delta Synthesized by Urea Auto-Combustion Method

Polycrystalline NaCo2O4-delta 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 NaCo2O4-delta is about 620 degrees 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 degrees 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 degrees C have some growth trend along a-b planes, while the grains on the surface of the pellet sintered at 950 degrees C show an obvious growth trend toward c-axis.