The Relation between the Mechanical and Piezo-Electrical Properties of a Rochelle Salt Crystal

Abstract

Stress-strain curves for a Rochelle salt crystal for 16 to 36\ifmmode^\circ\else\textdegree\fi{}C.---A crystal cut so as to give maximum piezo-electric response under compression, was mounted so that a known force was applied to the center of a brass block resting on the top, and the corresponding strain was measured to within ${10}^{\ensuremath{-}6}$mm by means of an optical extensometer described by S. R. Williams. Variation with piezo-electric charge. When the load is applied, the initial strain is less than the final strain by an amount proportional to the initial piezo-electric charge, the difference varying with the temperature and reaching a maximum for 22.25\ifmmode^\circ\else\textdegree\fi{}, the temperature of maximum piezo-electric response. For a stress of 2225 gm/${\mathrm{cm}}^{2}$, the strain with the is less than the no charge strain by an amount 0.7 \ifmmode\times\else\texttimes\fi{} ${10}^{3}$ per coulomb per ${\mathrm{cm}}^{2}$; for this stress the initial and final strains were 9.5 and 13.4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}5}$, the corresponding moduli being 2.32 and 1.62, both times ${10}^{10}$ dynes. The final strain is independent of temperature; it is not proportional to stress, being 7.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}5}$ for 1 kg/${\mathrm{cm}}^{2}$ and 12.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}5}$ for 2 kg/${\mathrm{cm}}^{2}$.