Ammonium Hydrogen Sulfate: A New Ferroelectric with Low Coercive Field

Abstract

(N${\mathrm{H}}_4$)HS${\mathrm{O}}_4$ is ferroelectric in the temperature range between -3°C and -119°C. The symmetry of the room-temperature phase is $\frac{P{2}_1}{c}$; the ferroelectric phase is also monoclinic, with space group $\mathrm{Pc}$; and the lowest phase, which is piezoelectric, has triclinic symmetry $P1\mathrm{}$. All three phases are pseudo-orthorhombic. The coercive field is very low: about 150 v/cm at -13°C. The spontaneous polarization $P_s$ is about 0.4 μcoul/${\mathrm{cm}}^2$ at that temperature, and rises to a maximum of about 0.8 μcoul/${\mathrm{cm}}^2$ just above -119°C. $P_s$ falls to zero abruptly at the lower transition point. The higher transition is of second order, and the lower of first order.