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 alpha-SnS to monoclinic gamma-SnS was observed at 18.15 GPa. The fit of a Birch-Murnaghan equation-of-state gave the volume at zero pressure of V-0 = 192.6(3) Angstrom(3), the bulk modulus at zero pressure of B-0 = 36.6(9) GPa. and the pressure derivative of the bulk modulus B' = 5.5 (2) for alpha-SnS and V-0 = 160(1) Angstrom, B-0 = 86.0(5) GPa and B' = 4 for gamma-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.