Pressure-induced structural phase transition in the IV-VI semiconductor SnS

The structural behaviour of SnS under high-pressure has been investigated by angular dispersive synchrotron powder diffraction up to 38.5 GPa. A structural phase transition from orthorhombic α-SnS to monoclinic γ-SnS was observed at 18.15 GPa. The fit of a Birch-Murnaghan equation-of-state gave the volume at zero pressure of V₀ = 192.6(3) ų, the bulk modulus at zero pressure of B₀ = 36.6(9) GPa and the pressure derivative of the bulk modulus B′ = 5.5(2) for α-SnS and V₀ = 160(1) Å, B₀ = 86.0(5) GPa and B′ = 4 for γ-SnS. The improper ferro-elastic transition is of first-order and is accompanied by a large volume discontinuity of about 9.1%. The phase transition can be described in terms of a group/subgroup relationship. The doubling of the unit cell indicates a wavevector (1/2, 0, 1/2) at the U-point in the Brillouin zone.