Observation of discrete molecular structures in glassy PxSe1-x by Raman spectroscopy

We report conclusive evidence for the existence of molecular local ordering in four phosphorus-selenium glasses. The compositions were chosen to span the P-rich glass-forming region and were P2Se, P3Se, P4Se, and P0.84Se0.16. Raman spectra show unequivocally the existence in each glass of well-defined P4Se3 cage molecules. All nine Raman-active internal modes of this molecule have been observed, with a clear trend of reduction of their intensity as the P content is increased. We find that these materials behave as a matrix-supported assembly of P4Se3 molecules.