Dielectric Study on the Effect of Hydrostatic Pressure on the Phase Transitions in the System of {(NH₄)₃H(SO₄)₂}_1-x{(ND₄)₃D(SO₄)₂}_x

Abstract

The concentration-pressure-temperature three dimensional phase diagram of {(NH 4 ) 3 H(SO 4 ) 2 } 1- x {(ND 4 ) 3 D(SO 4 ) 2 } x system was studied by means of dielectric measurements in a pressure-temperature range of \(p{\lesssim}10\) kbar and -100^°\(C{\lesssim}T{<}\text{room temperature}\). The two pressure-induced ferroelectric phases of VI and VII in the normal compound ( x =0) are found in lower pressure region as the concentration x increases. Compounds with x >0.90 show the ferroelectric VI phase even at atmospheric pressure. A good correspondence between the effects of hydrostatic pressure and deuterium-substitution was established as regards the stability of the ferroelectric phases. Two pressure-induced phases (Phases VIII, IX) were newly observed in the normal-deuterated mixed crystal system.