Effect of hydrostatic pressure on the phase transitions in {N(CH3)4}2ZnI4, {N(CH3)4}2CdI4, {N(CH3)4}2HgCl4, AND {N(CD3)4}2MnCl4

The effect of hydrostatic pressure on the phase transitions in {N(CH 3 ) 4 } 2 XY 4 (XY 4 = ZnI 4 , CdI 4 , HgCl 4 ) and in a deuterated compound of {N(CD3) 4 } 2 MnCl 4 have been studied. The intermediate monoclinic phase in the -ZnI 4 compound narrows as pressure increases, and disappears at 176 MPa. The transition temperatures in the -CdI 4 and -HgCl 4 compounds increase linearly with increasing pressure with the rates of 0.22 K/MPa and 0.20 K/MPa, respectively. The pressure-temperature phase diagram of {N(CD 3 ) 4 } 2 MnCl 4 is similar to that of the hydrogen compound. The appearance of the dielectric-constant peak in the incommensurate phase shifts towards about 35 MPa higher pressure by deuteration.