Mn and As doping of β-FeSi2via a chemical method

Abstract

β-FeSi₂ was doped with Mn and As via the chemical reduction of the glassy phase of [{Fe₂O₃·4SiO₂} + Mn₂O₃ + Mn₃O₄] and [{Fe₂O₃·4SiO₂} + As₂O₃] respectively, using Mg-metal at 800 °C. Iron silicide doping was investigated using high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray analysis (EDX) and Hall measurements. The increment in the inter-planar distance, as verified by the SAED image and XRD peak shift, indicates both As and Mn doping. The Raman defect (D) peak at 300 cm⁻¹ confirms As and Mn doping. The red shift in the Raman peaks at 190 cm⁻¹, 244 cm⁻¹ and 300 cm⁻¹ due to increases in the bond lengths indicates significant doping. In addition, the upshift in the binding energy of the Si 2p XPS peak and the downshift in the binding energy of the Fe 2p³ peak indicate As and Mn doping in β-FeSi₂. Also, the low intensity As 3d and Mn 2p³ XPS peaks considerably confirm doping, which is in close agreement with the EDX result. The Hall measurements show that the As doped sample is n-type, while the Mn doped sample is p-type. The carrier concentration in the Mn doped sample is higher than that of the As doped sample, which can be justified by the higher activation energy and using two-band model theory.