Effects of mechanical alloying methods on structural phase stability, chemical state, optical, electrical and ferroelectric properties in Sc-doped α-Fe2O3 system

Abstract

The development of metal doped α-Fe₂O₃ (hematite) based wide band gap semiconductors with high electrical conductivity, high electrical polarization and wide optical band gap is a challenging problem and also useful for application point of view. In this work, a substantial enhancement of electrical conductivity, optical band gap and ferroelectric polarization have been recorded at room temperature for Sc doped α-Fe₂O₃ system. Two different methods of the mechanical alloying and subsequent heat treatment have been used to synthesize the samples of α-Fe_2-xSc_xO₃ oxide (x = 0.2–1.0). The X-ray diffraction patterns have confirmed formation of single-phased Rhombohedral structure for low Sc doping content (x = 0.2), whereas a mixture of Rhombohedral-structured α-Fe₂O₃ type phase and cubic-structured Sc₂O₃ type phase has been formed for the higher Sc contents (x = 0.5 and 1.0). The phase fractions varied depending on the amount of Sc content, chemical reaction during mechanical alloying of the elementary oxides and solid-state reaction during the heat treatment. Response of the Sc₂O₃ type phase in Raman spectra is sensitive depending on the methods of inter-mixing the α-Fe₂O₃ and Sc₂O₃ by mechanical alloying. X-ray photoelectron spectroscopy (XPS) confirmed the metal (Fe, Sc) ions in +3 charge state, although the samples for low Sc content x = 0.2 showed a signature of Fe⁺² and Sc⁺⁴ states. A detailed analysis of the Fe 3s XPS band confirmed a strong 3s-3d spins exchange coupling of strengths 1.18 eV–1.34 eV.