Fig. 1. XRD patterns of samples under different milling time

Fig. 2. SEM patterns of samples under different milling time
(a): 0 h; (b): 10 h; (c): 20 h; (d): 40 h

Fig. 3. FTIR spectra of samples under different milling time

Fig. 4. Enlarged spectra in three wavebands under different ball milling time
(a): Ⅰ wave band: 425~660 cm^-1; (b): Ⅱ wave band: 845~868 cm^-1; (c): Ⅲ wave band: 1 320~1 525 cm^-1

Fig. 5. Smooth fitting and second derivative spectra in Ⅰ wave band (425~660 cm^-1) under different ball milling time
(a): 0 h; (b): 10 h; (c): 20 h; (d): 40 h

Fig. 6. Changes of peak area with ball milling time
(a): Peak at 473 cm^-1; (b): Peak at 540 cm^-1

Fig. 7. Smooth fitting and second derivative spectra in Ⅱ wave band (845~868 cm^-1) under different ball milling time
(a): 0 h; (b): 10 h; (c): 20 h; (d): 40 h

Fig. 8. Area change of peak centered at 856 cm^-1 with ball milling time

Fig. 9. Smoothing curve fitted and second derivative spectra in Ⅲ wave band(1 320~1 525 cm^-1) under different ball milling time

Fig. 10. Area change of peak around at 1 446 cm^-1 with ball milling time