Abstract
The effect of Fe and La doping in SnO2 structure have been investigated by synthesizing the material using mechanical alloying and post-heat treatment under ambient and non-ambient atmospheres. The material has been characterized by employing Powder X-ray Diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV–Visible spectroscopy, and Broadband dielectric spectroscopy. The material has formed bi-phased lattice structure, consisting of tetragonal phased SnO2 structure (space group P 42/m n m) and a secondary phase, for the samples that were mechanically alloyed in air and heat treated in different atmospheres. The α-Fe2O3 (space group R- 3 c) has been identified as the secondary phase for Fe doped SnO2 system and small amount (5%.) of La2O3 (cubic structure with space group I a-3) has been identified as the secondary phase for mechanically alloyed (in air) La doped SnO2 system. The N2 atmosphere played a crucial role in forming the single-phased SnO2 structure in mechanically as-alloyed samples and also for determination of the phase fraction in bi-phased lattice structure during the incorporation of Fe and La in SnO2 system. XPS confirmed the multiple charge states for Fe (Fe3+, Fe2+, Fe0) and Sn (Sn4+, Sn2+) ions. The bandgap energy in the Fe and La-doped SnO2 system has reduced in the range of 2.18 eV–2.37 eV and 2.81 eV–2.90 eV, respectively in comparison to band gap ∼ 3.6-3.8 eV for SnO2 system. The band gap reduction has been controlled mainly by the SnO fraction in SnO2 structure. The electrical conductivity of Fe and La-doped samples has been found in the order of ∼ 10−7 S/cm to 10−9 S/cm. The Fe-doped samples have shown higher electrical conductivity than the La-doped samples. The nitrogen environment during mechanical alloying or heat-treatment played a significant role in determining high electrical conductivity and dielectric constant, and low dielectric loss constant of the samples.
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