Superconductivity and enhancement of critical current density of Ta-substituted TlSr1212 with addition of nanosize MgO

Abstract

In this paper, the authors report the effect of nanosize MgO particles addition on superconducting and transport critical current density Jc of TlSr1212 superconductors prepared from Tl0·9Bi0·1Sr1·95Ta0·05Ca0·9Y0·1Cu2O7 starting composition using conventional solid state synthesis. X-ray diffraction analyses of Tl0·9Bi0·1Sr1·95Ta0·05Ca0·9Y0·1Cu2O7+xMgO (x=0 to 0·8 wt-%) showed formation of dominant 1212 phase (>90 vol.-%) together with minor 1201 phases. Undoped TlSr1212(x=0) was observed to superconduct with a zero-resistance critical temperature Tc zero of 65 K. The x=0·2 sample recorded the highest Tc zero (80 K) but for higher x, Tc zero was gradually suppressed. The effect of the MgO addition also caused Jc enhancement in zero field with highest value at x=0·2. Using the self-field approximation model, the variation of Jc with temperature for x=0 to 0·4 samples indicate that MgO addition reduces the characteristics length Lc associated with the pinning force. Jc measurements in external magnetic field of 0–0·8 T showed smallest drop in Jc at x=0·2. The Jc enhancements in self-field and in the external fields are suggested to be due to increased flux pinning of the samples as a result of the MgO addition.