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 a few previously unexplored periodates A2BIO6 (A = alkali metal; B = Bi, Sb, In, Tl, Ga). Our compositional phase diagram analysis reveals two compounds Na2BIO6 (B = Bi, In) that 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 the valence band maxima (VBM), while alloying Tl in Na2BiIO6 introduces an intermediate band (Tl s character) below the conduction band minima. These alloys, Na2Bi0.25In0.75IO6 and Na2Tl0.25Bi0.75IO6, acquire Eg's of 1.66 and 1.78 eV, respectively. Apart from band gap, the antibonding VBM, favorable optical absorption, highly dispersive band edges, and well-positioned VBM (for efficient oxygen evolution reaction) make these compounds highly promising for PV and PEC applications.