Room Temperature Dielectric Properties of Polycrystalline FeTe_1−x Se _x (x = 0.0–0.5)

Abstract

In this work, frequency-dependent dielectric properties of polycrystalline samples with nominal compositions FeTe_1−x Se _x (x = 0.0–0.5) were investigated. The samples were synthesized via solid-state reaction method with intermittent grinding at ambient pressure. The phase formation, lattice properties and chemical compositions of the samples were analysed. Dielectric constants ($\varepsilon ^{\prime }$, $\varepsilon ^{\prime \prime }$), dielectric loss (tan δ) and alternating current (AC) conductivity (σ _ac) as a function of frequency ranging from 100 Hz to 10 MHz were measured at room temperature. X-ray diffraction (XRD) data showed the presence of impurity phases of Fe₃O₄, FeTe₂ and hexagonal FeSe/Fe₇Se₈. Both a and c lattice parameters decreased with the substitution of Se. Energy-dispersive x-ray spectroscopy confirmed the increasing ratio of Se/Te with x. The measured negative values of real dielectric constant ($\varepsilon ^{\prime } )$ for x = 0.0–0.5 indicate the conductive nature of these samples. As the Se content was increased, the $\varepsilon ^{\prime }$ became more negative as a result of better grain connectivity as shown by the higher AC conductivity and dielectric loss.