The crystalline phases in the sample before and after the thermal analysis
were identified by powder X-ray diffraction (XRD; RINT2500, Rigaku). The hightemperature
powder XRD measurementswere carried out by using a Bruker AXS D8
Vario-1 equipped with a capillary heater stage (mri, Physikalische Gerate GmbH).
The sample for the XRD measurement was kept in Ar atmosphere by using a cell
with a window of kapton film or by sealing it in a quartz capillary tube with Ar gas.