Abstract
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 D-2d(12) phase to orthorhombic C-2v(j not equal 19) phase at 126 K and sigma(6) = 1.12
kbar, and (ii) from orthorhombic C-2v(19) phase to the same orthorhombic C-2v(j not equal 19) phase as before, at 110 K and sigma(6) = 0.3 kbar.
The reversibility paths of these metastable phases are discussed and an
explanation to the appearance of the C-2v(j not equal 19) phase, based
on the Gibbs Free energy density of the system, is presented.
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