Cluster formation in expanded fluid mercury and dilute amalgams near the liquid-gas critical point

Abstract

The optical absorption spectrum and the thermopower have been measured for expanded fluid Hg and dilute amalgams containing 0.2 at.% Bi and 0.2 at.% Cd at temperatures and pressures up to 1600°C and 2100 bar. The optical gap closes around 8 g/cm 3. Above 4 g/cm 3 an additional absorption band with negative slope appears in the near-infrared region and grows rapidly with increasing density. The shape of this near-infrared band is appreciably changed by the addition of a multivalent element such as Bi, while it remains unchanged when the divalent Cd is added. The thermopower for Hg remains negative and attains an extremely large value in the vicinity of the critical point. It is suggested that the results may be interpreted by assuming the existence of dielectric clusters in the critical region.