Infrared properties of Mg-doped LaFeO3 prepared by sol–gel method

Abstract

A perovskite LaFe1−x Mg x O3 (x = 0, 1/3) compound was prepared by the sol–gel method and characterized by TG–DTA, XRD, SEM, and XPS. The infrared (IR) emissivity of the nanoscale LaFe2/3Mg1/3O3 powder synthesized after heat preservation for 2 h at 1300 °C was as high as 0.93 in the range 0.2–2 μm, an increase of 121 % than that of undoped LaFeO3. The increase in the IR emissivity of LaFe2/3Mg1/3O3 can be mainly attributed to the substitution of Mg2+ with Fe3+ in the LaFeO3 lattice. The substitution of Mg2+ with Fe3+ introduced the energy level of Fe4+ impurity and generated oxygen vacancies, thus increasing the impurity and oxygen vacancy absorption. The lattice distortion caused by doping strengthened the lattice vibration absorption. The polaron hopping of electrons between Fe3+ and Fe4+ also significantly strengthened the absorption properties within the corresponding spectrum area of Mg2+-doped LaFeO3. The absorptivity of LaFeO3 was stable at ~0.94 in the range 200–500 nm and decreased drastically after 500 nm, and the absorption edge was ~600 nm. The absorption of Mg-doped LaFeO3 sample was 0.93 in the range 200–2000 nm. Mg doping significantly improved the absorptivity of LaFeO3 (0.75); moreover, the absorption edge red-shifted to the spectral region at ~2000 nm. This was caused by the introduction of Mg2+ that increased the oxygen vacancy concentration in LaFeO3 valence band and enhanced the intraband absorption, thus strengthening the absorptivity to some extent.