Influence of topology on vibrational dynamics of Pd-based bulk metallic glasses

Topology in amorphous structures relates to the characteristics of specific-atomic configurations that exist in a structure. Relative sizes and numbers of atoms comprising a structure are likely to control its topology. These two characteristics become primary parameters for exploring topological similarities and distinctions between systems. The understanding of vibrational spectra and topology of bulk metallic glasses (BMGs) is important for acquiring knowledge about their structural aspects. To explore vibrational dynamics, analytical expressions for the phonon frequencies of BMGs are derived both for longitudinal and transverse modes of vibrations based on a simple model. The model assumes a central force effective between nearest neighbours, and a volume dependent force. The phonon frequency expressions reproduce the main characteristic features of the dispersion curves in Pd-based BMGs: Pd39Ni10Cu30P21, Pd40Ni40P20, Pd32Ni48P20 and Pd64Fe16P20. These BMGs are topologically similar as suggested in the atomic structural model proposed recently by Miracle and the similarity of topological arrangements of the constituents in these Pd-based BMGs influences their vibrational dynamics and leads to the similar dispersion curves, thus provide relevant information regarding the structural aspects of the alloy systems.