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\ifmmode^\circ\else\textdegree\fi{}C and -119\ifmmode^\circ\else\textdegree\fi{}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 $P1$. All three phases are pseudo-orthorhombic. The coercive field is very low: about 150 v/cm at -13\ifmmode^\circ\else\textdegree\fi{}C. The spontaneous polarization ${P}_{s}$ is about 0.4 \ensuremath{\mu}coul/${\mathrm{cm}}^{2}$ at that temperature, and rises to a maximum of about 0.8 \ensuremath{\mu}coul/${\mathrm{cm}}^{2}$ just above -119\ifmmode^\circ\else\textdegree\fi{}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.