Electrical-mechanical coupling due to charged dislocations

Abstract

A theory for the relationship between the mechanical damping, compliance defect, piezoelectric moduli and electric susceptibility due to charged dislocations is discussed. A damping and piezoelectric (direct and converse) experiment on a single crystal of KCl at 40 kHz and strain amplitudes of 1·6 × 10⁻¹⁰ to 1·5 × 10⁻⁵ is reported. The method is shown to be suitable for the measurement of a piezoelectric modulus as small as 5 × 10⁻¹⁹ coulomb/newton. The mechanical damping, compliance defect and piezoelectric modulus are found to be strongly amplitude dependent above a strain of 3 × 10⁻⁷. From this experiment the charge on the dislocations is calculated to range between 1 and 3% of the maximum allowed on a dislocation. The behaviour of this measured charge with strain amplitude suggests that the damping is due to charged dislocations interacting with their compensating charge clouds. The charge cloud radius of 13 Å calculated from the impurity concentration agrees favourably with the value of 20 Å obtained from the experimental results suggesting that the restrictions on the theory for eV ∞/kT>l are not severe. The electric susceptibility due to charged dislocations is estimated as 10⁻⁴.