Evidence for Low-Temperature Melting of Mercury owing to Relativity

摘要

Mercury shows very unusual physical and chemical properties in the gas, liquid, and solid states, resulting in many known anomalies within the Group 12 series of elements. For example, the superconductivity transition temperature of mercury (T_c = 4.153 K) is unusually high compared to both zinc (0.875 K) and cadmium (0.56 K); mercury crystallizes in a rhombohedral structure in contrast to zinc and cadmium: the latter two elements adopt a hexagonal closed-packed structure; and the melting point of mercury (T_m = 234.32 K) is unusually low compared to those elements (692.68 K for Zn, 594.22 K for Cd).Thus, mercury is the only elemental metallic liquid at room temperature, and it has the highest density amongst all liquids under normal conditions. It has long been speculated that these observed anomalies could be due to strong relativistic effects, but this has never been confirmed.