On the high-temperature phase transitions of some KDP-family compounds: A structural phase transition? A transition to a bulk-high proton conducting phase?

摘要

Thermal analysis, X-ray diffraction, and impedance analysis were used to study the high-temperature nature of the KDP-family compounds: KH_2PO_4 (KDP), RbH_2PO_4 (RDP) and CsH_2PO_4 (CDP). Our results show that the structural phase transition from tetragonal to monoclinic modification in KDP and RDP earlier reported at around T_p approximately equals 180 °C and T_p approximately equals 86 °C, respectively, does not exist. For CDP we found that the structural phase transition from a monoclinic to a cubic symmetry superprotonic phase above 230 °C does not take place. Instead, in close agreement with Lee's suggestion, we found evidence that at all these temperatures a partial polymerization takes place at reaction sites distributed on the surface of the samples.