Ab-initio Discovery of Stable Double Perovskite Oxides Na2BIO6 (B=Bi, In) with Promising Optoelectronic Properties.

Recently, oxide perovskites are garnering tremendous attention from the scientific community as possible alternatives to the currently used active materials in photovoltaic(PV) and photoelectrochemical(PEC) devices. Herein, we report the stability and promising optoelectronic properties of few previously unexplored periodates A2BIO6, (A=alkali metals; B=Bi, Sb, In, Tl, Ga). Our compositional phase diagram analysis unveils two compounds Na2BIO6, (B=Bi, In) to stabilize in monoclinic phase at thermodynamic equilibrium, showing band gaps (Eg) in the visible region. Band engineering via alloying Bi in Na2InIO6, introduces Bi-6s lone pair bands above valence band maxima (VBM), while alloying Tl in Na2BiIO6 introduces an intermediate band (Tl-s character) below conduction band minima. These alloys Na2Bi0.25In0.75IO6 and Na2Tl0.25Bi0.75IO6 acquire Egs of 1.66 eV and 1.78 eV, respectively. Apart from band gap, antibonding VBM, favorable optical absorption, highly dispersive band edges and well positioned VBM (for efficient oxygen evolution reaction), makes these compounds highly promising for PV/PEC applications.