High-pressure electrical resistivity and Moossbauer spectroscopic studies on narrow band Co0.8Fe0.2S2 nanoparticles up to 8 GPa

Pyrite-structured Co0.8Fe0.2S2 colloid nanoparticles, synthesized using solution method with particle distribution around 3-4 nm determined by transmission electron microscope, were studied under high pressure up to 8 GPa using Fe-57 Mossbauer spectroscopy and electrical resistivity techniques. Drastic decrease in T-C by magnetic measurements indicated nanosize of the particle. Higher quadrupole splitting (QS) at ambient condition was due to large lattice strain and electric field gradient generated by higher surface to volume ratio of these nanosized particles. Under pressure, Mossbauer parameters - isomer shift and QS - showed an expected trend up to similar to 5.6 GPa. Above 6.4 GPa, the QS remained constant up to 8 GPa with decreased value. Even after decompression, the high-pressure phase is retained. The variation of pressure coefficient of electrical resistivity from -0.021/GPa to -0.151/GPa across 6.8 GPa suggested a second-order phase transition. The coincidence of observed value with that of the bulk suggested that the particle size does not impart much influence on transition pressure. This is the first report on nanoparticles of Co0.8Fe0.2S2 under pressure.