Pressure-induced Pb-Pb bonding and phase transition in PbSnO.

High-pressure single-crystal to 20 GPa and powder diffraction measurements to 50 GPa, show that the structure of PbSnO strongly distorts on compression with an elongation of one axis. A structural phase transition occurs between 10 GPa and 12 GPa, with a change of space group from Pbam to Pnam. The resistivity decreases by more than six orders of magnitude when pressure is increased from ambient conditions to 50 GPa. This insulator-to-semiconductor transition is accompanied by a reversible appearance change from transparent to opaque. Density functional theory-based calculations show that at ambient conditions the channels in the structure host the stereochemically-active Pb 6s lone electron pairs. On compression the lone electron pairs form bonds between Pb ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands.