Intermediate valency state of samarium chalcogenides under high pressure
Samarium chalcogenides undergo isostructural phase transitions under pressure and samarium ions turn into an intermediate valency state (IVS). The thermo EMF S and electroresistance rho of SmS, SmSe and SmTe under pressure to 12 GPa and in the temperature range 30-400 degrees C have been measured to investigate properties of the IVS and its stability limits. Hydrostatic pressure to 8 GPa and quasi-hydrostatic pressure to 12 GPa on monocrystals have been realised in 'toroid' cells. It is found that the IVS is stabilised after phase transitions at pressures of 0.65 GPa in SmS, 3.4 GPa in SmSe and 5.2 GPa in SmTe. Transition to IVS is accompanied by sharp anomalies in rho and S. It is shown that IVS exists in a wide pressure range (at least to 12 GPa). The zone structure model for these compounds is suggested.