Structural and optical properties of sol-gel synthesized LaFe1-xAgxO3

The band-gap energy of LaFeO3 is successfully tuned by substitution of Fe by monovalent Ag+. The physical properties of the as-synthesized nanopowders are evaluated using various structural and spectroscopic characterization techniques and supported with first principles calculation. All LaFe1-xAgxO3 nanopowders (x = 0, 0.02, 0.03, 0.04, 0.05) exhibit an orthorhombic crystal structure with increased a and c lattice parameters and that of the b parameter decreased when the silver content increases. The latter also contributed to the formation of highly porous crystallites with inter-pore spacings in the order of the nanometer. Moreover, the incorporation of silver shows a lattice distortion in particular the Fe-O bond which is responsible for the reduction of the band-gap energy value. Therefore, an additional iron valence state, Fe2+, is created along with that of the original one, Fe3+. Density functional theory calculation suggests that silver ions are more likely positioned at (a/2, 0, c/2) coordinates in the unit cell. The efficiency of such silver incorporation is demonstrated due to the band-gap energy red-shift (from 2.39 eV, for x = 0, to 1.9 eV, for x = 0.05) caused by the decrease in the minimum of the conduction band. This ability to control the energy value of the band-gap in multiferroic materials is very promising for photovoltaic applications.