The collective dynamics of the ‘non-simple’ liquid metal Sn

The dynamic structure factor S(Q, ω) of liquid Sn was measured at 320 °C and 1000 °C in a Q-range between 2 nm−1 and 30 nm−1 using inelastic X-ray scattering. The obtained spectra clearly demonstrate the existence of longitudinal propagating modes in this liquid metal. At 320 °C a positive dispersion is found in the low Q-region, where the mode velocity is about 12% larger than the bulk adiabatic speed of sound. At 1000° this so-called ‘positive dispersion’ reduces to about 6%. The quasielastic lineshape contains a Gaussian contribution near the Q-positions of the first maximum in S(Q), which has not yet been reported in simple liquid metals like, e.g. the liquid alkalis. With increasing temperature, the relative Gaussian contribution increases and can be observed along a wider Q-range. This anomaly is related to a partially covalent nature of liquid Sn in analogy to other liquid non-simple metals.