The differing responses of various techniques in measuring the phase transformations of K2ZrF6

Abstract The compound K 2 ZrF 6 undergoes an unusual multistep solid-solid transformation on temperature variation, whose irreversibility or reversibility depends on the target temperature: heating K 2 ZrF 6 up to only 250 °C results in an irreversible process, while heating over this temperature results in reversible transformation. The reversibility of the back transformation indicates that α-K 2 ZrF 6 transforms to a high-temperature phase (HTF rev ) on heating above 250 °C, and on cooling reverts to the α-K 2 ZrF 6 phase. The irreversible transformation involves transformation of α-K 2 ZrF 6 to a high-temperature phase (HTF irrev ) on heating to 250 °C, and then on cooling transforming to a mixture of meta-K 2 ZrF 6 and K 3 ZrF 7 . With time this mixture changes to α-K 2 ZrF 6 , meta-K 2 ZrF 6 and K 3 ZrF 7 . This transformation was monitored by DTA, DSC, 19 F MAS NMR, XRD and thermal diffusivity techniques. Surprisingly, these experimental techniques showed unexpectedly differing responses.