Properties of Guanidine Aluminum Sulfate Hexahydrate and Some of Its Isomorphs

Abstract

Guanidine aluminum sulfate hexahydrate (C${\mathrm{N}}_{3}$${\mathrm{H}}_{6}$)Al${(\mathrm{S}{\mathrm{O}}_{4})}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}6${\mathrm{H}}_{2}$O is ferroelectric from as high a temperature as it will stand for a short time (about 200\ifmmode^\circ\else\textdegree\fi{}C), down to temperatures of liquid ${\mathrm{N}}_{2}$, the lowest we have employed. The crystal is trigonal, with the ferroelectric polarization along the trigonal axis. The 60-cycle hysteresis loops are often biased or have the character of double loops. The shape of the loop is correlated with the location of the specimen in the mother crystal. At room temperature the saturation polarization is about 0.35 microcoulomb/${\mathrm{cm}}^{2}$, the coercive force at 60 cycles/sec is about 1000-3000 volts/cm. These quantities increase with decreasing temperature. The small signal dielectric constant is about 6 along the axis and about 5 perpendicular to it. Of isomorphous substances, those so far examined in which ${\mathrm{D}}_{2}$O replaces ${\mathrm{H}}_{2}$O, in which ${\mathrm{Ga}}^{+3}$ and ${\mathrm{Cr}}^{+3}$ replace ${\mathrm{Al}}^{+3}$ and in which ${(\mathrm{S}\mathrm{e}{\mathrm{O}}_{4})}^{2\ensuremath{-}}$ replaces ${(\mathrm{S}{\mathrm{O}}_{4})}^{2\ensuremath{-}}$, show essentially the same properties. The switching characteristics resemble those of BaTi${\mathrm{O}}_{3}$ but the present crystals are considerably slower.