Tunable band gaps from anion ordering and octahedral tilting in oxyfluorides*

Heteroanionic materials are currently receiving increased interest because they may support superior functionality than single-anion materials [1]. In perovskite structures, anion ordering combined with octahedral tilting provides new degrees-of-freedom (DOFs) from which to manipulate the chemical, physical and electronic properties. This control has been shown to tune the band gap in oxynitrides, but oxyfluorides remain underexplored [2,3]. Here we discuss the results of first-principles calculations on the experimentally known wide-band gap semiconductor, KNaNbOF5 [4], and show that octahedral tilting and anion ordering can be used to tune the band gap. We show how the combination of these DOFs make it possible to decrease the band gap so it resides in the visible range. Finally, these results will be used to propose a design strategy for creating novel photovoltaic materials.

[1] H. Kageyama, et al. Nat. Com., 9(1):772, 2018
[2] A. Kubo,et al. Chem. of Mat., 29(2):539–545, 2017.
[3] Nathalie Vonrti and U. Aschauer, Phys. Rev. Mat. 2, 105401, 201
[4] R. A. F. Pinlac, et al. Crys., 1(1):314, 2011.