The crystalline stability of the

Phase analysis was performed by X-ray powder diffraction analysis (XRD, Rigaku Corp., Rint 2500, Cu Kα, 40 kV, 300 mA). Intensities were collected in the 2θ range between 20° and 80° with a step size of 0.02° and a measuring time of 2 s at each step at room temperature. Lattice parameters were obtained by refining the XRD patterns with MDI Jade 6.0 software.