Turnbull, Robin and González-Platas, Javier and Liang, Akun and Jiang, Dequan and Wang, Yonggang and Popescu, Catalin and Rodriguez-Hernandez, Placida and Munoz, Alfonso and Ibáñez, Jordi and Errandonea, Daniel, Pressure-Induced Phase Transition and Band-Gap Decrease in Semiconducting Na3bi(Io3)6. Available at SSRN: https://ssrn.com/abstract=4257696 or http://dx.doi.org/10.2139/ssrn.4257696
Abstract
We report a combined experimental/theoretical high-pressure study of Na3Bi(IO3)6 under compression to 11.2 GPa at ambient temperature. Through a combination of single-crystal and powder synchrotron X-ray diffraction, optical absorption measurements and ab initio density functional theory calculations we unambiguously show a first-order pressure-induced phase transition at around 9.5 GPa from the ambient pressure phase, referred to here as α−Na3Bi(IO3)6, to a new crystalline structure referred to here as β−Na3Bi(IO3)6. The triclinic (P-1) to triclinic (P1) phase transition is characterised by a doubling of the primitive cell volume, whereby the crystallographic b-axis doubles in length, and by a decrease in the volume per formula unit of approximately 3%. The phase transition is also characterised by an indirect → indirect electronic bandgap decrease of approximately 0.1 eV as measured by absorption spectroscopy (3.44(1) → 3.32(1) eV) and calculated via density functional calculations (2.48 → 2.33 eV). We also report the pressure evolution of the crystal lattice parameters and isothermal compressibility tensor of the ambient pressure phase α−Na3Bi(IO3)6, which reveals highly anisotropic compressibility and a bulk modulus of 30.4(7) GPa.