Temperature and pressure induced phase transition in IV-VI compounds

Abstract

The crystal structure of SnS has been investigated as a function of temperature by elastic neutron scattering from 293 K to 1 000 K. SnS undergoes a second order displacive phase transition from the α-phase (B16, Pbnm) to the high temperature β-phase (B33, Cmcm) at 887 K. The mean square displacement of the Sn atom which is isotropic at room temperature becomes increasingly anisotropic and anharmonic near Tc. Energy dispersive X-ray diffraction experiments have been performed on IV-VI semiconductors PbS, PbSe, PbTe, GeS, GeSe, SnS and SnSe as a function of hydrostatic pressure to 340 kbar. PbS, PbSe and PbTe undergo transition from the NaCl type (B1) phase to the orthorhombic phases (B33 or B16) at about 22, 45 and 60 kbar, respectively. The orthorhombic phases of PbS and PbSe have been found to be of TlI type (B33, Cmcm) and that in PbTe has been found to be GeS type (B16, Pbnm). PbS, PbSe and PbTe undergo further phase transitions to the cubic CsCl type (B2) phase at about 215, 160 and 130 kbar, respectively. The orthorhombic IV-VI compounds GeS, GeSe, SnS and SnSe do not undergo any phase transition up to 340 kbar

Structures of two intermediate phases between the B1 and B2 phases of PbS under high pressure

“…The diffraction patterns obtained at higher than 45.4 GPa can been indexed to the B2 phase, and this is consistent with previous reports. 6,7,12 Two experimental factors influenced the precise structural determination in our previous two experimental runs. As shown in Fig.…”

“…Using resistance measurements, Samara et al found that PbS has a phase transition at 2.3-2.5 GPa. 4 X-ray diffraction (XRD) studies have shown that the B1 phase transforms into an intermediate phase at 2-3 GPa, [5][6][7][8][9][10][11][12] and into a CsCl-type structure (B2) at higher than 21.5 GPa. 6,7 However, the detailed structure of the intermediate phase is controversial.…”

“…It has been proposed to be Pnma 5 or Cmcm. 6,7,[9][10][11][12] Using angle dispersive XRD studies, Maclean et al found that the intermediate phase could be considered to be a GeS-like structure and can be indexed as a monoclinic structure when including weak reflections. 8 Similarly, various results have been obtained when using different theoretical calculations.…”

The high-pressure ?/? phase transition in lead sulphide (PbS)

“…First structural studies under high pressure were performed using X-ray film methods [8]. Later, the compression behaviour of PbS was studied by means of highpressure energy dispersive X-ray powder diffraction (HP-EDX) up to 35 GPa [9,10,11,12,13].…”

“…The phase transition at 2.2 GPa [7] to a β-phase having orthorhombic symmetry was characterised as a first order transition [8,10,11]. However, the structure of this phase is still a matter of debate.…”