X-ray diffractograms were obtained with an X-ray diffractometer
(D8 Discover,Bruker Co.) under operating conditions as follows: the X-ray generator was run at 40 kV and 40 mA,
and the scanning angle 2 h was set from 4 to 45 at a scanning rate of
0.1 /min.
Crystallinity (%) was defined as the percentage ratio of diffraction peak area to total diffraction area.