Local Structure and Superconducting Properties of Bi ₂ Te ₃ -Doped YBa ₂ Cu ₃ O _{7 − δ}

Abstract

The samples of (Bi₂Te₃) _x (YBa₂Cu₃ O _7−δ) _1−x (x = 0, 2.5 %) have been synthesized at normal pressure, and the effect of the doping of topological insulator Bi₂Te₃ on the superconductor YBa₂Cu₃ O _7−δ is studied. The diamagnetism properties are investigated by zero-field cooling DC magnetization measurement. In the Bi₂Te₃-doped sample, an enhancement of superconducting fractions is observed, and the superconducting transition temperature (T _c ) increases. For the sample with x= 2.5 %, the phase transition of the tetragonal phase to the orthorhombic phase is observed by X-ray diffraction, and the increase of the degree of local structure disorder is confirmed by extended X-ray absorption fine structure, so it can be concluded that the superconducting fraction enhancement is attributed to the phase transition induced by the addition of topological insulator Bi₂Te₃. Scanning electron microscopy images show that the added Bi₂Te₃ is found to adhere to the surface of YBa₂Cu₃ O _7−δ grains, and it is considered that the strain induced by grains’ interaction leads to the phase transition which enhances the degree of local structure disorder at the same time. An absorption edge shift to the high-energy side is observed by the X-ray absorption near-edge structure. The edge shift can be attributed to the electron transfers from YBa₂Cu₃ O _7−δ to the additives. It is widely accepted that the hole intensity is closely related with T _c , so in YBa₂Cu₃ O _7−δ the added holes by the transition may lead to the enhancement of T _c . Thus, it can be concluded that the topological insulators can produce structural and electronic effect on the YBCO superconductors in the composite materials.