Synthesis and Characterizations of Arsenic Doped FeSe Bulks

Experimental data collected for the preparation of the manuscript: "Synthesis and Characterizations of Arsenic Doped FeSe Bulks"J. Supercond. Nov. Magn. 38, 109 (2025)Abstract:FeSe(11) family has a simple crystal structure belonging to iron-based superconductors (FBS) and has many stable phases including hexagonal and tetragonal structures, but only the tetragonal phase exhibits the superconductivity. In this study, we have investigated the effects of chemical pressure induced by As-doping at Se sites in the FeSe system by preparing a series of FeSe1-xAsx (x = 0.005, 0.01, 0.02, 0.05, 0.1 and 0.2) bulks. A broad characterization has been performed on these samples using structural, microstructural, transport and magnetic measurements. The obtained lattice parameters are increased by As-doping, which suggests the successful insertion of As at Se sites into the tetragonal lattice for low doping contents up to 5%, whereas the higher As substitution appears in the form of the FeAs impurity phase. The temperature dependence of the resistivity of all samples has similar behaviour and depicts the highest onset transition temperature of around 11.5 K, but the zero resistivity is not reached until the measured temperature of 7 K, which could be due to the presence of the impurity phases. Our study suggests that a dopant with a large ionic radius, i.e. arsenic, promotes the formation of the hexagonal phase of the 11 family and is effective for a small amount of doping level for the superconducting properties, whereas higher As-doping levels reduce the superconducting properties.[In the published article, Figure 2 and Figure 3 is Elemental mapping for the constituent elements and scanning electron microscope (SEM) image of FeSe1-xAsx, respectively]Fig. 1 Powder X-ray diffraction patterns (XRD) at room temperature for the prepared samples FeSe1-xAsx at ambient pressure with x = 0.01, 0.05, 0.1 and 0.2. FeAs, hexagonal (Fe7Se8) and Pt phases are observed as the impurity phases. The Pt impurity phase is observed from the XRD sample holder.Fig. 2 Elemental mapping for the constituent elements of FeSe1-xAsx polycrystalline samples: a–e x = 0.005; f–j x = 0.05 and k–o x = 0.2. For each sample, the first image depicts a scanning electron microscope (SEM) image, and the last image represents the combined image of Fe, Se and As elements. The rest of the images are the elemental mapping of the individual elements.Fig. 3 Backscattered electron image (BSE; AsB) of the samples with a–c x = 0.005, d–f x = 0.05 and g–i x = 0.2 samples. Bright, light grey and black contrasts correspond to Fe7Se8 (hexagonal phase), FeSe1-xAsx and pores, respectively. The black contrast may indicate the presence of the FeAs phase in certain locations.Fig. 4a The variation of resistivity with temperature for all the samples up to the room temperature (300 K). b The variation of low temperature resistivity with temperature ranges from 7 to 20 K. The insets of these figures (a) and (b) illustrate the resistivity variation for the doping content x = 0.1.Fig. 5: The temperature dependence of the normalized magnetic moment (M/M5K) with an applied magnetic field of 50 Oe for FeSe1-xAsx with x = 0.05 and x = 0.2 in zero-field cooling (ZFC) and field cooling (FC) modes. The inset figure shows the variation of the normalized magnetic moment for the sample x = 0.05.Fig. 6 The variation of a room temperature resistivity (ρ300K) and b the onset critical temperature Tc.onset from the resistivity measurements with As-doping content (x).