TGA experiments were carried out using Q600 SDT thermal analysis machine (TA Instruments, USA) under a flow of nitrogen. The sample weight used was about 20 mg, and the temperature ranged from 38 °C to 1000 °C with a ramping rate of 20 °C min−1. X-ray diffraction patterns were recorded on a D/Max-3C X-ray powder diffractometer (Rigalcu Co., Japan), using a Cu-K α source fitted with an Inel CPS 120 hemispherical detector. SEM micrographs were performed using a Quanta 200 scanning electron microscope equipped with an energy dispersive spectrometer (Philips-FEI Co., the Netherlands).