Pressure-temperature phase diagram of multiferroic Ni3 V2 O8

The pressure-temperature phase diagram of multiferroic Ni3 V2 O8 is investigated for hydrostatic pressures up to 2 GPa. The stability range of the ferroelectric phase associated with the incommensurate helical spin order is reduced by pressure and ferroelectricity is completely suppressed at the critical pressure of 1.64 GPa at 6.2 K. Thermal expansion measurements at ambient pressure show strong steplike anomalies of the lattice parameters associated with the lock-in transition into the commensurate paraelectric phase. The expansion anomalies are highly anisotropic; the related volume change is consistent with the high-pressure phase diagram.