Supersoftening of transverse phonons in ${\mathrm{Zr}}_{41}{\mathrm{Ti}}_{14}{\mathrm{Cu}}_{12.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{22.5}$ bulk metallic glass

Acoustic properties and low-temperature specific heat of ${\mathrm{Zr}}_{41}{\mathrm{Ti}}_{14}{\mathrm{Cu}}_{12.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{22.5}$ alloy in glassy, fully crystallized and equilibrium crystalline states have been investigated. It is found that a large amount of free volume is quenched in the bulk metallic glass (BMG) which is obtained at a low-cooling rate, even fully crystallization cannot remove all the free volume from the alloy. A supersoftening of long-wavelength transverse acoustic phonons in the BMG relative to its equilibrium crystalline state is observed. The origins for the phenomenon are discussed. The finding has significance for understanding of the glassy state as well as the excellent glass forming ability of the glass forming alloy.