Pressure-induced phase transition and band-gap decrease in semiconducting Na3Bi(IO3)6.

[Display omitted] • New high-pressure induced phase transition in semiconducting Na 3 Bi(IO 3) 6. • Pressure induced bandgap decrease in Na 3 Bi(IO 3) 6. • Highly anisotropic compressibility of Na 3 Bi(IO 3) 6. • Experimental/theoretical high-pressure study of non-centrosymmetric Na 3 Bi(IO 3) 6. • Single-crystal synchrotron X-ray diffraction, optical absorption measurements and ab initio density functional theory calculations on Na 3 Bi(IO 3) 6. We report a combined experimental/theoretical high-pressure study of Na 3 Bi(IO 3) 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- Na 3 Bi(IO 3) 6 , to a new crystalline structure referred to here as β- Na 3 Bi(IO 3) 6. The triclinic (P -1) to triclinic (P 1) 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- Na 3 Bi(IO 3) 6 , which reveals highly anisotropic compressibility and a bulk modulus of 30.4(7) GPa. [ABSTRACT FROM AUTHOR]