Ferroelectric Transition in Rubidium Bisulfate

Abstract

RbHS${\mathrm{O}}_{4}$ is ferroelectric below -15\ifmmode^\circ\else\textdegree\fi{}C. The room-temperature phase is monoclinic, with space group $\frac{P{2}_{1}}{c}$, $a={14.35}_{6}$ A, $b={4.62}_{2}$ A, $c={14.80}_{7}$ A, $\ensuremath{\beta}=121.0\ifmmode^\circ\else\textdegree\fi{}$ and $Z=8$. The symmetry of the ferroelectric phase is $\mathrm{Pc}$, as established by systematic x-ray absences and the fact that spontaneous polarization appears along the $c$ axis below -15\ifmmode^\circ\else\textdegree\fi{}C. Both the high- and low-temperature phases are pseudo-orthorhombic. The dielectric constant ${\ensuremath{\epsilon}}_{c}$ at 10 kc/sec and for a field of 5 v/cm is 10 at room temperature; as the temperature is lowered, ${\ensuremath{\epsilon}}_{c}$ rises to a sharp peak of \ensuremath{\sim}240 at -15\ifmmode^\circ\else\textdegree\fi{}C and falls to \ensuremath{\sim}5 at -196\ifmmode^\circ\else\textdegree\fi{}C. The transition appears to be of second order. No second transition, as in the case of isomorphous N${\mathrm{H}}_{4}$HS${\mathrm{O}}_{4}$, could be detected in the temperature range -15\ifmmode^\circ\else\textdegree\fi{}C to -196\ifmmode^\circ\else\textdegree\fi{}C.