On the nature of KH2PO4 high-temperature phases

The KDP (KH2PO4) undergoes a high-temperature phase transition (HTPT) at 453 K ± 10 K. A detailed analysis of the nature of the phase transitions using x-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), impedance spectroscopy (IS) and Fourier transform infrared spectroscopy (FTIR) was carried out. As a result, we could successfully interpret the physicochemical properties related to KDP's high-temperature behavior. We found that depending on the thermal treatment extent at 519 K, different phases are present on KDP; after 2 hours of treatment, KH2PO4 → KnH2PO3n+1 (n>1) are present, and above 8 hours of treatment, only KH2PO4 → KPO3 are present. The presence of KPO3 is proved by chemical analysis. The presence of KPO3 is checked by chemical analysis. Showing the existence of the HTPT accompanied by the formation of polyphosphate.