Pressure Effect on the Phase Transition in (CH3)2NH2H2AsO4 and Its Isotope Effect.

The effect of hydrostatic pressure on the phase transition of (CH 3 ) 2 NH 2 H 2 AsO 4 was investigated by dielectric measurement at high pressure up to about 1.5 GPa. A pressure-induced phase for (CH 3 ) 2 NH 2 H 2 AsO 4 was newly observed above 1.36GPa at room temperature. The transition to the pressure-induced phase shows first order character. The effects of hydrostatic pressure on the ferroelectric transition temperatures for both crystals of (CH 3 ) 2 NH 2 H 2 AsO 4 and (CH 3 ) 2 N(H 0.5 D 0.5 ) 2 (H 0.5 D 0.5 ) 2 AsO 4 were dielectrically investigated. As the pressure increases, the transition temperatures for both crystals monotonously decrease. Their pressure derivatives, dT c /dp, were obtained to be -49 ± 1 K/GPa for (CH 3 ) 2 NH 2 H 2 AsO 4 and -52 ± 1 K/GPa for (CH 3 ) 2 N(H 0.5 D 0.5 ) 2 (H 0.5 D 0.5 ) 2 AsO 4 . From the present experimental results, the lack of an appreciable isotope effect on dT c /dp was observed in (CH 3 ) 2 NH 2 H 2 AsO 4 .

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