ULTRASONIC VELOCITY AND ATTENUATION IN KCL AND KBR CONTAINING LI

The temperature and stress dependence of the ultrasonic velocity and attenuation in KCl and KBr containing Li+ was measured by the pulse-echo technique in the frequency range 10-150 Mc/sec, and in the temperature range 1.6°-77°K. Only the T2g mode interacts with the Li+ in KCl indicating that the Li+ is displaced from the lattice site in the 〈111〉 directions. In KBr the Li+ appears to be on the lattice site since no acoustic interaction was observed. The experimental results agree well with the classical elastic dipole theory. The 'shape factor' (λA-λB) of the elastic dipole ellipsoid is (6.6±0.6) × 10-2 as compared with 6.3 × 10-2 calculated on the basis of the lattice distortion derived by Hatcher et al. Annealing and aging experiments indicate that Li+ precipitates even at low concentrations and at room temperature. With increasing concentration N interactions between the defects are observed, but there is no evidence that this is a cooperative phenomenon. The elastic losses are proportional to 1/T and N; a good theoretical model is still missing. © 1968.