Effect of partial substitution of iron for group IV elements on the structure and superconducting properties of the Fe(Se$_{0.2}$Te$_{0.8}$)$_{0.82}$ compound

The structure and superconducting properties of the Fe$_{1-x}$(A)$_x$(Se$_{0.2}$Te$_{0.8}$)$_{0.82}$ ($x$ = 0.1, 0.2) compound, where A is Cu, Zn, Bi or Group IV elements (Pb, Sn, Ge), were studied. It was shown that the effect of substitution of some iron atoms on the structure and superconducting properties of the Fe(Se,Te) compound depends on whether a solid solution with a substituting element was formed. If complete dissolution of the replacement element occured (Cu, Zn), then a significant degradation of the superconducting properties was observed. If a separate chalcogenide phase was formed (substitution by Pb, Sn, Ge), then a slight change in the superconducting properties was observed. Such a slight change and even improvement in the superconducting properties upon precipitation of the chalcogenide phase can be associated with both the positive effect of an increase in the relative content of iron and a decrease in the number of iron atoms in the interstitial sites of the $\beta$-phase. The preservation of the superconducting properties of the Fe(Se,Te) compound with a small substitution of iron for group IV elements can be used to create wires based on Fe(Se,Te), since impurity chalcogenide particles can act as effective pinning centers.