Structural phase transition and optoelectronic properties of lead-free AgNb1-xTaxO3 (x=0, 0.5 and 1) perovskite systems

Crystal phases Pbcm (monoclinic), Cmcm (orthorhombic), P4/mbm (tetragonal) and Pm3<overline>m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Pm\overline{3 }m$$\end{document}(cubic) of the perovskite AgNbO3; Pm3<overline>m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Pm\overline{3 }m$$\end{document} (cubic) of AgNb0.5Ta0.5O3; and R3c (rhombohedral), P2/m (monoclinic), Cmcm (orthorhombic), P4/mbm (tetragonal) and Pm3<overline>m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Pm\overline{3 }m$$\end{document} (cubic) of AgTaO3 have been studied using DFT. To investigate stable crystal phases, cohesive energies and formation enthalpy are calculated demonstrating that P4/mbm, Pm3<overline>m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Pm\overline{3 }m$$\end{document} and P2/m are the stable phases of AgNbO3, AgNb0.5Ta0.5O3 and AgTaO3 respectively. The electronic properties are examined through the mBJ exchange potential in their stable structural phases reveal that allAgNb1-xTaxO3 (x = 0, 0.5 and 1) perovskites are direct band gap semiconductors with energy gaps of 1.686, 1.973 and 2.1 eV respectively. Previous studies reported an indirect band gap of 2.97 eV for AgTaO3. These systems are semiconductors with ideal band gaps, leading to a wide array of applications including dielectric and photocatalytic devices. The optoelectronic properties of these compounds suggest that they are promising candidates for optical devices such as LEDs, photodiodes, quantum wells and solar cells in the visible region of the electromagnetic spectrum.