Second pressure derivatives of the second-order elastic constants of some alkali halides

The second pressure derivatives of the rocksalt-type alkali halides NaCl, KCl, LiF, and NaF have been calculated from a knowledge of their third- and fourth-order elastic constants. The value of the second pressure derivative of C111 for both KCl and NaCl is found to be very large and positive, indicating possible plastic deformation in these compounds at moderate pressures of the order of 7 bars. © 1988 The American Physical Society.