Physical properties and crystal structure of polonium

Measurements of the physical properties, and crystal structure of polonium show that the element is very metallic. Measurements of the electrical resistivity of thin films of metal show that polonium exists in two allotropic forms. The specific resistivity and thermal coefficient of resistivity of the two phases are respectively: Roof a-Po=42micro-ohm-cm aofa-Po=.0046 Roofb -Po=44micro-ohm-cm a ofb-Po=.0070. The element has a melting point of 254°C and a density of 9.4 g/cc. Its hardness is similar to that of lead;X-ray diffraction studies have shown that alpha-Po has a simple cubic structure with a lattic parameter a = 3.34 A. The beta-phase has a simple rhombohedral structure with a = 3.36 A and alpha = 98° 13\u27;A sample which was photographed intermittently for 138 days---the half life of Po---has shown no new diffraction patterns, thus indicating that lead is soluble in polonium to the extent of 50 atomic percent;Diffraction patterns taken with the Sample of different temperatures show that alpha-polonium has a negative thermal coefficient of expansion equal to -300 +/- 100 x 10-6 cm/cm/°C. The coefficient of expansion for beta-polonium is probably 50 x 10 -6