The mixture was stirred at 70 C for 2 h. The gel was obtained after drying at 130 C for 1 h. To determine the crystalline phase, the acquired precursor was ground in an agate mortar and then heat treated at a heating rate of 300 C/h from room temperature to 700, 800, 900, 1000,1100, 1200, and 1300 C for 5 h, respectively.