Elastic constants of amorphous and single-crystal Pd40Cu40P20

We have measured the adiabatic second-order elastic constants of amorphous Pd40Cu40P20 (isotropic, two independent elastic constants) and single-crystal Pd40Cu40P20 (tetragonal, six independent elastic constants) over the range 3.9 < T < 300 K. Below ∼20 K, the elastic constants of single-crystal Pd40Cu40P20 vary as C(T) = C(0)[1 − bT2 − dT4], which is the same temperature dependence found in metallic elements. In contrast, below ∼20 K the elastic constants of amorphous Pd40Cu40P20 vary as C(T) = C(0∗)[1 − aT]. The bulk modulus of amorphous Pd40Cu40P20 is approximately 2% lower than that of crystalline Pd40Cu40P20, whereas the shear modulus of the glass is 13–36% lower than the four independent shear moduli of the tetragonal crystal. The lower moduli of the glass are best explained by additional atomic displacements, beyond those experienced by the atoms in a crystal, that occur because the atoms in glasses do not occupy centers of symmetry.