Variable temperature PXRD measurements were conducted on a PANalytical X'Pert Pro MPD diffractometer (Malvern PANalytical, Espoo, Finland) equipped with an Anton Paar HTK1200N oven (Wundschuh, Austria) using Cu Kα radiation. In vacuo measurements were conducted at <10 -3 mbar. The temperature was raised in 5 °C steps from 25 to 200 °C, with the measurements performed after equilibration of each step. The diffractograms were evaluated using Origin software.