The Electrical Property Of CoSb₃and SmFeO₃under High Pressure

Thermoelectric material has a function for energy conversion and has been usedin thermoelectric generator and thermoelectric cooler which have the advantages ofsmall volume, light weight, firmness, and no noise, mechanical compressionrefrigeration machine incomparable advantages, and will not cause any pollution tothe environment, long service life and easy to be controlled. Skutterudite compoundCoSb₃is a typical thermoelectric material and obtained more and more attention.However, there is very little research concerning the properties of CoSb₃underextreme conditions, such as under high pressure. Because the electrical properties arethe key factor to determine the application value, so it is necessary to study theelectrical properties of CoSb₃under high pressure.In this work, using diamond anvil cell device （DAC） equipped with in-situelectrical measurement devices, the resistivity variation of CoSb₃under high pressurehas been studied. At the same time, the structural characteristics of CoSb₃underextreme compression were also analyzed by the first principle calculation.The results are as following:（1） In the compression process, the resistivity of CoSb₃declines with pressureincreasing. When the pressure reaches19.6GPa, a discontinuous change in resistivityoccurs. This pressure point is much closed to that the structural phase transition（20GPa） happened at, indicating that the change in resistivity of CoSb₃is caused bythe structural phase transition. In the unloading process, the resistivity of CoSb₃maintained a gentle upward trend, does not appear inflection point, indicating that thephase transition is irreversible, which is consistent with the earlier report.（2） Using the first-principles calculation, the band structure of CoSb₃underdifferent pressure was obtained. At ambient pressure, CoSb₃is a direct band gapsemiconductor with a band gap of0.189eV. With pressure increasing, the width ofband gap increases. When pressure reaches20GPa, CoSb₃become an indirect band gap semiconductor. With pressure increasing further, the width of band gap remainsalmost unchanged.The calculation results show that there is no energy gap decrease during wholecompression process, indicating that resistivity decreases with pressure increasing isnot determined by the energy band compression. The discontinuous changes inresistivity and energy band occurred around20GPa can be attributed to the structurephase transition.The electrical properties of SmFeO₃under high pressure have been studied byAC impedance spectroscopy method, and the pressure dependent resistance change ofthe sample has been obtained. The discontinuous change in resistance has been foundat12.32GPa.