Elastic and piezoelectric constants of the cuprous halides

Elastic and piezoelectric constants of CuCl, CuBr, and CuI have been measured. The elastic constants of zinc-blende-structure materials when plotted on a reduced scale indicate a striking instability as the Phillips critical ionicity (0. 785) is approached. CuCl is the most piezoelectric of these materials with a piezoelectric constant e14=0.41 C/m2 at 80°K.