DFT calculations of the structural, elastic, and electronic properties of (Bi_1−xFe_x)₂Te₃ chalcogenides

Abstract

The crystal structure and elastic and electronic properties of (Bi1-xFex)2Te3 were studied by first-principles calculations within the Density Functional Theory (DFT) scheme. We found that at zero GPa, the lattice parameters for Bi2Te3 are in good agreement with the available experimental and theoretical data. As Fe replaces bismuth, the lattice parameter a increases while c decreases, changing the unit cell volume. According to Born’s structural stability criterion, the system is mechanically stable. Poisson’s ratio suggests a change from brittle to ductile behavior for (Bi1-xFex)2Te3 as iron increases. Also, Poisson’s ratio indicates that there is an ionic-covalent bond for x = 0.00 and behave as a metal as iron content increases. Vickers hardness decreases its value as Fe is introduced in the compound. Band structure calculations show that the results with spin orbit coupling (SOC) and without SOC are in good agreement with the experimental results. With SOC, a direct band gap at the  point is obtained with Eg = 0.138 eV concerning the 0.226 eV obtained without SOC. An evident modification of crystal structure in (Bi1-xFex)2Te3 shows a consistent trend, indicating a significant impact of iron incorporation on the structural properties. The electronic properties show a significant transformation with the introduction of iron, Bi2Te3 is characterized by a band gap, through iron doping the electronic structure shows a complete elimination of the band gap, marking a transition from semiconductor towards a conductor-like behavior. Density of states analysis provided insight into these changes, illustrating a modulation of electronic properties dependent on iron content.