Discovery of a new nontoxic cuprate superconducting system Ga-Ba-Ca-Cu-O

Superconductivity is observed in a new nontoxic cuprate system Ga-Ba-Ca-Cu-O, with T c = 82 K for GaBa 2 Ca 5 Cu 6 O 14 + δ ( 5 (Ga-1256) and T c = 116 K probably for GaBa 2 Ca 3 Cu 4 O 10+δ (Ga-1234) or GaBa 2 Ca 2 Cu 3 O 8+δ (Ga-1223), respectively. All compounds are fabricated by solid state reaction method under high pressure and high temperature. Samples are characterized by resistivity, magnetization and X-ray diffraction (XRD) measurements. The temperature dependence of magnetization measured in both zero-field-cooled and field-cooled processes on one sample (S1) shows two superconducting transitions at about 82 K and 113 K. The estimated shielding fraction for the phase with T c of 82 K is about 67%, while the fraction for another phase with T c of 113 K is quite small. The XRD Rietveld refinement for S1 indicates two main phases existing in the sample, Ga-1256 with fraction of about 58% and non-superconducting Ca 0.85 CuO 2 with fraction of about 42% respectively. Thus, we can conclude the superconducting phase with transition temperature of 82 K is due to Ga-1256. The resistivity measurement also confirms the superconductivity for S1, and the resistivity reaches zero at about 82 K. The temperature dependence of magnetization for another sample (S2) shows much higher superconducting shielding fraction for the phase with T c of 116 K, which may be a promising prospective for the synthesis of Ga-1234 or Ga-1223 phase.