Phase diagram uniaxial pressure—temperature of KDP

In this work we present for the first time the uniaxial pressure-temperature phase diagram of KDP, for temperatures near the ferroelectric phase transition at 122 K. It is observed from Raman measurements that under uniaxial pressure the KDP undergoes two metastable transitions: (i) from tetragonal D122d phase to orthorhombic Cj≠192v phase at 126 K and σ6 = 1.12 kbar, and (ii) from orthorhombic C192v phase to the same orthorhombic Cj≠192v phase as before, at 110 K and σ6 = 0.3 kbar. The reversibility paths of these metastable phases are discussed and an explanation to the appearance of the Cj≠192v phase, based on the Gibbs free energy density of the system, is presented.

Keywords:

• Raman spectroscopy
• phase transitions
• phase diagram

Notes

Universidade Federal do Para, Belem, Para, Brazil

Universidade de Brasilia, Brasilia, DF, Brazil