The high-pressure alpha/beta phase transition in lead sulphide (PbS): X-ray powder diffraction and quantum mechanical calculations

TL;DR

This study combines X-ray diffraction experiments and quantum mechanical calculations to investigate the high-pressure phase transition in lead sulphide, revealing detailed structural and elastic property changes during the alpha/beta transition.

Contribution

It provides new experimental and theoretical insights into the alpha/beta phase transition mechanism and elastic properties of PbS under high pressure.

Findings

Beta-PbS crystallizes in CrB-type structure (Cmcm)

The alpha/beta transition is first order with ~5% volume change

Transition involves a gliding mechanism of {001} bilayers

Abstract

The high-pressure behaviour of PbS was investigated by angular dispersive X-ray powder diffraction up to pressures of 6.8 GPa. Experiments were accompanied by first principles calculations at the density functional theory level. By combining both methods reliable data for the elastic properties of rock-salt type alpha- and high-pressure beta-PbS could be obtained. beta-PbS could be determined to crystallise in the CrB-type (B33), with space group Cmcm. The reversible ferro-elastic alpha/beta transition is of first order. It is accompanied by a large volume discontinuity of about 5% and a coexistence region of the two phases. A gliding mechanism of {001} bilayers along one of the cubic <110>-directions governs the phase transition which can be described in terms of group/subgroup relationships via a common subgroup, despite its reconstructive character. The quadrupling of the primitive unit cell indicates a wave vector (0,0,pi/a) on the Delta-line of the Brillouin zone.