Theory of the Ferroelectric Effect and Clamped Dielectric Constant of Rochelle Salt

Using the crystal structure determination of rochelle salt made by Beevers and Hughes, a theory of the ferro-electric effect and clamped dielectric constant has been worked out using the displacement of the hydrogen nucleus in the 1-10 hydrogen bond as the ferroelectric dipole. This theory has only one disposable constant, $\beta$, the factor of proportionality between the polarization and the Lorentz internal field. Taking the oxygen separation found by x-rays, the dielectric constant for electrons and atoms found by experiment, and the number of molecules per cubic centimeter found from the x-ray cell determinations, the value of $\beta$ becomes 4.07 which agrees well with the theoretical value $\frac{4\pi }{3}$ for an isotropic substance. This theory accounts for the clamped dielectric constant at low field strengths, which as shown by measurements presented here, has maximum values at -18°C and +24°C, the Curie temperatures for the free crystal. This shows that the anomaly must lie in the clamped dielectric constant alone and not in the interaction of the clamped dielectric constant and the piezoelectric effect. This model also accounts for recent measurements of W. A. Yager which show that the dipole dielectric constant is relaxed at a frequency of about 5×${10}^9$ cycles.