First-principles structural, elastic and optoelectronics study of sodium niobate and tantalate perovskites.

The intensified quest for efficient materials drives us to study the alkali (Na)-based niobate (NaNbO) and tantalate (NaTaO) perovskites while exploiting the first-principles approach based on density functional theory, coded within WIEN2K. While using the Birch Murnaghan fit, we find these materials to be stable structurally. Similarly, the ab-initio molecular dynamics simulations (AIMD) at room temperature reveals that the compounds exhibit no structural distortion and are stable at room temperature. By using the recommended modified Becke-Johnson potential, we determine the electronic characteristics of the present materials providing insight into their nature: they are revealed to be indirect semiconductors with the calculated bandgaps of 2.5 and 3.8 eV for NaNbO and NaTaO, respectively. We also determine the total and partial density of states for both materials and the results obtained for the bandgap energies of these materials are consistent with those determined by the band structure. We find that both compounds exhibit transparency to the striking photon at low energy and demonstrate absorption and optical conduction in the UV region. The elastic study shows that these compounds are mechanically stable, whereas NaNbO exhibits stronger ability to withstand compressive as well as shear stresses and resists change in shape while NaTaO demonstrates weaker ability to resist change in volume. We also find that none of the compound is perfectly isotropic and NaNbO and NaTaO are ductile and brittle in nature, respectively. By studying the optical properties of these materials, we infer that they are promising candidates for applications in optoelectronic devices. We believe that this report will invoke the experimental studies for further investigation.