Synthesis of Fe and La doped SnO2 system in ambient and non-ambient conditions: Effect on lattice structure, chemical state, optical and dielectric properties

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.