High-pressure phase transitions in ordered and disordered Bi2Te2Se

Abstract

We report studies of pressure-induced phase transitions of ordered and disordered ternary tetradymite-like Bi₂Te₂Se by synchrotron powder X-ray diffraction (PXRD) in diamond anvil cells (DACs) for pressures up to 59 and 49 GPa, respectively. The first sample (SB) was prepared from a single crystal with ordered Se/Te sites while the second sample (Q) was prepared from a quenched melt resulting in disordered Se/Te. This allows for an investigation of the effect of disorder on the phase transitions and the equation of states (EoS) of the tetradymite-like α phase. Fitting of a third order Birch–Murnaghan EoS to the α phases yielded bulk moduli K₀ of 34.5(10) and 38.3(17) GPa and K′ of 6.2(3) and 5.0(5) for the SB and Q samples, respectively. An electronic topological transition (ETT) was identified in both samples at pressures of 4.4 and 3.1 GPa, respectively. This was followed by a transition near 11 GPa to a phase that is isostructural with the β phase of Bi₂Te₃. The Se/Te ordering only affects the transition pressure to a small extent. A cubic phase that resembles the δ phase observed in high-pressure studies of Bi₂Te₃ appears at 17–20 GPa, but the ternary composition leads to a more complex structure. The presence of a low angle diffraction peak in the δ phase demonstrates that the true structure is not simply body-centred cubic. In this way the samples resemble Bi₂Se₃ where Bi and Se show a high degree of ordering, but the proposed structure of δ-Bi₂Se₃ also does not fully describe the data for δ-Bi₂Te₂Se.