Investigation of the high pressure phase BiS2: Temperature-resolved structure and compression behavior to 60 GPa

Abstract

BiS2 was synthesized using a multi-anvil large volume press at a pressure and temperatures of 5.5 GPa and 1250 °C, respectively, and was then recovered at ambient conditions. Using data collection from single crystal synchrotron X-ray diffraction experiments, the crystal structure was found to consist of two distinct distorted square-based pyramidal BiS5-units. Synchrotron powder X-ray diffraction in the 85–300 K range shows smooth thermal expansion with a modest anisotropy. Physical property measurements reveals an optical band gap of 1.10 eV and a heat capacity with no anomalies in the 2–300 K range. Debye temperatures, determined by both heat capacity and thermal motion analysis, agree well with values of around 114 and 107 K for Bi1 and Bi2 atoms, respectively. Furthermore, theoretical calculations of the electronic band structure, by density functional theory, confirm the gapped state and reveal a small degree of band inversion at the Γ-point, but calculation of parity eigenvalues show BiS2 to possess a trivial topology. The high pressure behavior up to 60 GPa was investigated by powder diffraction in a diamond anvil cell; the structure is retained to at least 35 GPa while indications of a structure transition are observed afterwards. Fitting a 3rd order Birch-Murnaghan equation of state for pressures up to 30 GPa gives a bulk modulus of K0 = 35.5(8) GPa and K0′ = 7.37(18). Finally, a short structural comparison between the high pressure phase of BiS2 and BiS2-based superconductors is presented.