Piezoelectricity of Crystal Quartz

Abstract

Piezoelectricity of crystal quartz at constant temperature.---Experimental measurements with the quadrant electrometer of the distribution of the piezoelectric charge over the surface of a quartz crystal in a plane normal to the optic axis were found to vary in such a manner as to produce six regions of charge, three positive areas alternating with three negative. The areas had definite geometrical relations to the electric axes and therefore these facts yielded a new and accurate method of determining the directions of the electric axes in crystal quartz. In planes containing the optic axis there was a region of positive charge separated by a line in the direction of the optic axis from a region negative charge.Variation with temperature of the piezoelectric effect in quartz.---The piezoelectric effect increased by 20 percent from room temperature to 60^\circ\else\textdegree\fi{}C and decreased thereafter, reaching zero at about 573^\circ\else\textdegree\fi{}C. Cooling curves showed a lag.Variability of the piezoelectric effect.---The piezoelectric charge produced on different specimens or on different areas of the same specimen, all specimens being optically perfect, varied from large positive values of charge to large negative values. In general, the surface of the crystal quartz produced piezoelectric charges of the same sign, but of varying magnitudes. The charge measured over the entire surface of a crystal appeared to be the average of the effects of the elementary areas. The specimens in the present experiments varied on the negative side of the crystal from 5.8\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ to 7.1\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ e.s.u./${\mathrm{cm}}^{2}$\times\else\texttimes\fi{}dyne, while on the positive side the variation was from 4.9\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ to 6.4\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ e.s.u./${\mathrm{cm}}^{2}$\times\else\texttimes\fi{}dyne. These numbers are not far from the accepted value of 6.3\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ e.s.u./${\mathrm{cm}}^{2}$\times\else\texttimes\fi{}dyne, of the "piezoelectric constant" of P. and J. Curie. Such variations are in keeping with recent x-ray investigations on the imperfections of crystals which indicate that crystals are mosaics of an elementary perfect struture.