抄録
The pressure-temperature phase diagram of tetramethylammonium tetrachloromanganate {N(CH3)4}2MnCl4 was determined by dielectric measurements. As pressure increases the normal phase (I) to incommensurate phase (II) transition temperature (19.7°C at 0 MPa) increases. The region of commensurate phase with c=2c0 (III) becomes narrower with increasing pressure and disappears at about 125 MPa. A peak of dielectric constant along the a-direction is observed in a pressure range from 135 MPa to 240 MPa in the incommensurate II phase. The peak value decreases with increasing pressure. Above about 275 MPa the normal phase I directly transforms to the lowest temperature phase V (stable below −101°C on cooling at 0 MPa). The compound {N(CH3)4}2MnCl4 does not show ferroelectricity at high pressure unlike to the compounds of {N(CH3)4}2ZnCl4, {N(CH3)4}2CoCl4, and {N(CH3)4}2FeCl4.
