Thermal Expansion of Orthorhombic PbO

Thermal expansion of orthorhombic PbO was investigated by high‐temperature X‐ray diffraction. The coefficients in the a 0 , and c 0 directions are equal and <½ the coefficient in the b 0 direction. The structure is described in terms of Pb–O chains extended in the a 0 direction and bonded into layers in the b 0 direction; appreciable Pb–Pb bonding is indicated. Coordination and bond distances observed in PbSiO 3 and lead silicate glasses, which are similar to those of massicot, and Pb n O n polymeric units reported in PbO vapor are interpreted as additional evidence of the importance of PbO chains as structural entities.