Magneto Transport Properties of Superconducting LiTi1-xSnxO₄ Poly-crystals
ZHU JIA LEI LEI1*, Li-min Wang1, I-Nan Chen1
1物理系, 國立臺灣大學, 臺北市, Taiwan
* Presenter:ZHU JIA LEI LEI,
In this study, a high temperature solid phase method was used to synthesize lithium tetraoxodititanate (LiTi₂O₄) , and Sn4+ was doped by adding different proportions of SnO₂ to the solid phase to replace part of TiO₂ to produce tin-doped lithium tetraoxodititanate (LiTi2-xSnxO₄). X-ray diffraction was used to obtain the X-ray diffraction (XRD) pattern to confirm the product, It was found that polycrystalline LiTi₂O₄, LiTi1.98Sn0.02O₄, LiTi1.95Sn0.05O₄ and LiTi1.85Sn0.15O₄ samples were achieved for study. The lattice constants of samples are all close to the standard values of LiTi₂O₄. By measuring the change of magnetization M with temperature for the four samples, one can see that with the increase of Sn4+ doping, Tc does not change much, where Tconset is about 12 K, but the proportion of superconductor content decreases, according to the magnetic susceptibility at 2 K. By measuring the magnetization M(H) for the four samples at different temperatures, the lower critical magnetic field Hc1(T) and the upper critical magnetic field Hc2(T) can be obtained. The M(H) can confirm that LiTi2-xSnxO₄ is the type-Ⅱ superconductor with κ ≈ 6. The coherence length ξ can be calculated through the upper critical magnetic field Hc2; The coherence length ξ(0) of the sample LiTi₂O₄ is 5.971 nm, while the coherence length ξ(0) of the sample LiTi1.95Sn0.05O₄ is 8.549 nm, and one can see that ξ(0) will increase after doping. The London penetration depth λ is calculated by the lower critical magnetic field Hc1, the λ(0) of the sample LiTi₂O₄ is 40.59 nm, while the λ(0) of the sample LiTi1.95Sn0.05O₄ is 42.03 nm, and one can see that λ(0) is not much different with the Sn4+ doping. Combined with the λ(T) formula, it has a relationship with the temperature T in (Δλ(T))/(λ(0))≈√((πΔ0)/2T)exp(-Δ0/T), which conforms to the characteristics of s-wave superconductors.Moreover, using the Bean model to analyze the hysteresis curve, the temperature dependence of critical current Jc(T) is obtained. It is found that the maximum Jc is not at H = 0, but at H* = 400-1200 Oe , showing a trend of increasing first and then decreasing. The calculated pinning force Fp has similar properties, for samples with different Sn4+ doping. Using the Dew-Hughes model to the Fp(H) fit results, we infer that LiTi₂O₄ belongs to two-dimensional magnetic flux pinning. The H-T phase diagram of flux pinning in LiTi2-xSnxO₄ is obtained also.

Keywords: LiTi₂O₄, LiTi2-xSnxO₄, Doping, Type II Superconductivity, flux pinning