Electroacoustic investigations of charged dislocations in NaC1

Abstract

Abstract Internal friction, Young's modulus and polarization experiments have been conducted on NaC1 single crystals in order to determine the effect of mobile charged dislocations on dielectric, piezoelectric and elastic properties. The crystals are excited in their fundamental longitudinal mode of vibration at frequencies of about 80 kHz and at temperatures ranging from 78° to 301°k. Superposition of alternating electric fields (about 10 v/cm) on an alternating elastic field of identical frequency induces fractional changes in Young's modulus of about 4 p.p.m. at 78°k in deformed specimens. From these changes, an average value for the extrinsic piezoelectric constant Δd 23 of—9× 10−11 e.s.u./dyn is determined and values for the average dislocation charge per unit length Λ ranging from—5 to—11 × 10−6 e.s.u./cm are estimated. This value of Δd 23 is consistent with the absence of conclusive experimental evidence for direct or converse extrinsic piezoelectricity from dynamic measurements of polarization or ...