We describe an x-ray diffraction study of liquid Cs at high pressure and temperature conducted in order to characterize the structural changes associated with the complex melting curve and phase transitions observed in the solid phases. At 3.9 GPa we observe a discontinuity in the density of the liquid accompanied by a decrease in the coordination number from about 12 to 8, which marks a change to a nonsimple liquid. The specific volume of liquid Cs, combined with structural analysis of the diffraction data, strongly suggest the existence of $ds{p}^3$ electronic hybridization above 3.9 GPa, similar to that reported on compression in the crystalline phase.

• Received 30 November 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.125507