Pressure induced insulator-metal transition coupled with structural phase transition in BiSbTe1.25Se1.75 topological insulator

Using a Bridgman anvil cell, we have succeeded in measuring electrical resistivity at low temperatures and pressures up to 8 GPa nearly hydrostatically, which is demonstrated by the investigation into the pressure-induced insulator to metal transition of BiSbTeSe2 three-dimensional topological insulator (3D-TI) and the impact of pressure on structural properties was explored for the same compound using in-situ High pressure synchrotron powder X-ray diffraction with Diamond anvil cell technique up to 12 GPa. At room temperature, a Rhombohedra (R-3m) structure and a semiconductor-like ground state were found at ambient pressure. When the pressure is increased from 0 to 8 GPa, the values of normal state and low temperature resistivity, as well as the lattice constant and unit cell volume, decrease. High P triggers two structural phase transitions from Rombhohedral R-3m phase (9.8 GPa) to layered monoclinic C2/m phase (12.2 GPa) to BCC C2/c phase (20 GPa), leading to an increase in charge carrier density and a substantial decrease in normal-state resistivity. Surprisingly, the insulator-to-metal transition occurs around 6 GPa at 13.5 K and shift to 32.5 at 8 GPa. The Arrhenius equation was used to determine thermal activation energy at the high temperature region (>150 K), which can be seen to increase with P. Furthermore, the Variable Range Hopping model has been used to describe low temperature conduction (50 K T >150 K) and scattering phenomena in metallic regions (50 K, > 3.75GPa).