Structural and electronic phase transition in Bi2Se2.1Te0.9 under pressure

The phase evolution of Bi2Se2.1Te0.9 driven by the applied external pressure at ambient temperature was investigated in-situ with pressure up to 30.0(2) GPa using angle-dispersive X-ray diffraction (ADXRD) and Raman scattering spectroscopy. ADXRD measurements revealed that starting from the ambient rhombohedral structure (phase I), new forms of crystal structures are found to sequentially emerge with increasing externally applied pressure. Namely a seven-fold monoclinic structure (phase II), then an eight-fold monoclinic structure (phase III), a body-centered structure (BCC, phase IV), and finally a body-centered tetragonal structure (BCT, phase V) was observed at pressures of similar to 10.5(3) GPa, similar to 18.8(1) GPa, similar to 23.0(1) GPa, and similar to 28.0(2) GPa, respectively. The Raman scattering spectroscopy consistently showed that the pressures at which the corresponding phase appeared at similar to 10.2(2) GPa, similar to 18.9(1) GPa, and similar to 26.1(2) GPa, respectively. Moreover, the rhombohedral phase exhibited an even more pronounced signature of electronic topological transition in low-pressure regime, as compared with those previously observed in pristine Bi2Te3 and Bi2Se3. It appears that the alloying of Bi2Se3 with Bi2Te3 has led to more profound effects in the electronic and structural properties of the resultant system than that expected from the Vegard's law.