Synthesis and characterization of Ti-doped Bi4O4S3 superconductor
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The substitution effects of 3d2 transition metal Ti on the Bi4O4S3 superconductor structure were studied. The presence of Ti in Bi2O2 layer spacer or superconducting BiS2 layers was investigated. For this study, the polycrystalline Bi4O4S3 superconductor was prepared following a two-step solid-state reaction. Grains consisted of lamellae, ~ 5–10 μm in the planar orientation and 100–500 nm thick, presenting a tetragonal crystalline structure, with space group I4/mmm. For the first time, Raman spectroscopy revealed three modes at room temperature, with no significant changes in the spectra with Ti doping. The superconductivity was observed by the Meissner effect from ZFC and FC magnetization measurements. For both samples, the critical temperature was around 3.5 K, showing that Ti doping did not change the TC value, probably due to fact that Ti is in the Bi2O2 layer spacer. Also, the doped sample presented a strong positive magnetic moment, probably due to the presence of ferromagnetic order.
The authors are grateful to the C-LABMU/UEPG for the characterization facilities and also to Dr. O. F. Lima for the magnetization measurements. This work was partially financed by CNPq under contract no. 472.746/2013-8.
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