KH2PO4 is an archetypal ferroelectr

KH2PO4 is an archetypal ferroelectric material that has been investigated historically for a long time. In terms of the ferroelectric-to-paraelectric phase transition, it has been well known that it appears at ~ 150°C, where the low-temperature ferroelectric phase with an orthorhombic Fdd2 symmetry transforms into the paraelectric phase with a tetragonal symmetry. As can be seen from the temperature-dependent dielectric behavior of the cold-sintered KH2PO4 ceramics shown in Fig. 6, such a phase transition is manifested by a sharp dielectric abnormality at ~ 150°C, and this observation is consistent with the previous studies.