Colossal tuning of an energy gap in Sn2P2S6 under pressure

We report results of investigation of electrical and thermoelectric properties of Sn2P2S6 under strong compression up to 20 GPa. An "insulator-metal"(I-M)-type transition was discovered by a monotonic and reversible lowering of electrical resistivity by 9-10 orders. The energy gap (E-g = 2.3 eV) was estimated to decrease to similar to 0.25-0.3 eV at 20 GPa. X-ray diffraction and Raman studies on samples recovered from the high pressure experiments confirm a conservation of the original monoclinic lattice. Thus, a colossal "band-gap engineering" potential is revealed in this optical material. Sn2P2S6 is a potential candidate for emergent multi-functional switches, between transparent "insulator" state and conducting state with magneto-dependent properties. (C) 2011 American Institute of Physics. [doi:10.1063/1.3662926]