Elastic softness of amorphous tetrahedrally bonded GaSb and(Ge2)0.27(GaSb

We have measured the longitudinal and transverse acoustic wave velocities in bulk pressure-amorphized $a$-GaSb and $a\ensuremath{-}({\mathrm{Ge}}_{2}{)}_{0.27}(\mathrm{GaSb}{)}_{0.73}$ semiconductors and in their polycrystalline analogs. Although the densities of crystalline and amorphous states were practically equal, a significant softening of the bulk (29--35 %) and shear (41--46 %) elastic moduli has been found for amorphous phases. The ultrasonic data for bulk moduli are in good agreement with the previous direct volumetric measurements. Results of the present study combined with critical review of previous works allowed us to find specific features of elastic behavior of amorphous tetrahedral semiconductors (including group IV elements and group III-V compounds), and compare them to other classes of disordered solids.