Reversal in Optical Rotatory Power—"Gyroelectric" Crystals and "Hypergyroelectric" Crystals

A crystal is provisionally referred to as being "gyroelectric," when its optical rotatory power or gyration is nonzero at no biasing electric field and can be reversed in sign by means of a suitable biasing electric field. The gyroelectric crystals must be ferroelectric. It is found that, of the 19 kinds of regular ferroelectrics, only 9 kinds are gyroelectric. It is further shown that the other 10 kinds are divided into 5 "hypergyroelectric" and 5 optically inactive kinds. The rate of change of the gyration with the biasing electric field at zero value of the biasing electric field is provisionally referred to as the "electrogyration." The hypergyroelectric crystals are, somewhat roughly speaking, those crystals whose electrogyration is nonzero and can be reversed in sign by means of a suitable biasing electric field. Also, as a first step in the investigation of the properties of the gyroelectric and hypergyroelectric crystals, a theoretical inference is made into the change with temperature $T$ of the gyration $G_s$ at no biasing field and electrogyration $\eta$ of the gyroelectric and hypergyroelectric crystals in the neighborhood of their Curie temperature $T_0$. On some assumptions, the following are presumed. In the gyroelectrics, $G_s$ changes like ${(T_0-T)}^{\frac{1}{2}}$ with $T$ below $T_0$ and vanishes above $T_0$. In the hypergyroelectrics, $G_s$ changes linearly with $T$ both below and above $T_0$, but breaks at $T_0$. In the gyroelectrics, $\eta$ changes like ${(T_0-T)}^{-1\mathrm{}}$ below $T_0$ and changes like $2{(T-T_0)}^{-1\mathrm{}}$ above $T_0$. In the hypergyroelectrics, $\eta$ changes like ${(T_0-T)}^{\frac{-1\mathrm{}}{2}}$ below $T_0$ and vanishes above $T_0$.