Pressure-induced Pb–Pb bonding and phase transition in Pb₂SnO₄

Abstract

High-pressure single-crystal to 20 GPa and powder diffraction measurements to 50 GPa, show that the structure of Pb2SnO4 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 2 lone electron pairs. On compression the lone electron pairs form bonds between Pb2+ ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands.

Synthesis and Structure of Pb[C2O5]: An Inorganic Pyrocarbonate Salt

“…The presence of Pb 2+ raises the question of whether a stereochemically active lone electron pair is present. Stereochemically active lone electron pairs on large, polarizable ions such as lead or bismuth may persist up to very high pressures. − It is straightforward to identify them in DFT electron density difference maps, i.e., in isosurfaces depicting the difference between the self-consistent electron density distribution and an electron density distribution obtained by overlapping atomic electron density distributions. In such isosurfaces, stereochemically active localized electron pairs appear as umbrella-shaped maxima at difference densities of ≈0.03–0.04 e – /Å 3 at about 0.5 Å away for the ion position. − For Pb­[C 2 O 5 ], no such localized stereochemically active lone electron pairs were found at any pressure between 0 and 50 GPa.…”

Pressure-induced charge ordering transition in CaMn7O12

“…This mixture insulates the sample and wires from the tungsten gasket and acts as the pressure-transmitting medium. The epoxy-aluminum oxide is a nonhydrostatic pressure medium, which can introduce pressure gradients across the sample, however, our preparation method does not seem to substantially influence the transition width, as evidence by our calibration in [26]. Possible errors due to thermoelectric effects were avoided by alternating the direction of the current.…”

Pigments—Lead-based whites, reds, yellows and oranges and their alteration phases

“…Subsequent studies have further clarified the structure of the various compounds and broadened our knowledge about the use of these compounds in painting and glass production. The studies performed by Byström and Westgren (1943), Swanson et al (1972), Garnier et al (1976), Gavarri et al (1981), Gavarri (1982), Vigouroux et al (1982), Clark et al (1995) and Spahr et al (2020) have gradually clarified the characteristics and the thermally induced transformations occurring in the structures.…”

“…Modern lead stannate Pb 2 SnO 4 (lead-tin yellow type I) is produced by heating PbCO 3 and SnO 2 (generally in a 2:1 molar ratio) for a variable time (e.g., 1 week in Swanson et al 1972;6-12 h in Hashemi et al 1992), at temperatures between 750 and 1000 °C. This synthetic phase is characterised by edge-sharing SnO 6 -octahedra forming "chains along the c-direction, interconnected within the (001) planes with Pb 2+ ions" (Spahr et al 2020). Its structure was first assigned to the tetragonal space group P 4 2/mbc by Byström and Westgren (1943) and Swanson et al (1972) and then to the orthorhombic space group Pbam by Gavarri et al (1981).…”

“…Its structure was first assigned to the tetragonal space group P 4 2/mbc by Byström and Westgren (1943) and Swanson et al (1972) and then to the orthorhombic space group Pbam by Gavarri et al (1981). Spahr et al (2020) performed single crystal diffraction at ambient pressure on hydrothermally synthesised Pb 2 SnO 4 . They demonstrated that, although the Pbam space group has to be preferred, this lead stannate can be refined in both P 4 2/ mbc and Pbam space groups.…”