Synthesis, structural and physical properties of new Terbium containing Tb–Hg–Sr–Ca–Cu–O superconducting system

Abstract

Samples with various nominal compositions in the Tb–Hg–Sr–Ca–Cu–O system were prepared and studied by EDX, powder X-ray diffraction including the Rietveld refinement, electrical resistivity, magnetic susceptibility and thermoelectric power measurements. EDX and powder X-ray diffraction studies showed that Tb is required for the stabilization of the 1212, (Hg 1− y Tb y )Sr 2TbCu 2O 6+ δ ; y≈0.5 phase. Electrical resistivity and magnetic susceptibility measurements indicated that substitution of Tb by Ca is necessary to induce superconductivity in the 1212, (Hg 0.5Tb 0.5)Sr 2(Tb 1− x Ca x )Cu 2O 6+ δ samples. The Rietveld refinements of the X-ray data of two samples with x=0.0 and 0.5 were carried out on the basis of tetragonal symmetry (space group P4/ mmm) and the results indicated that the phase with x=0.5 has less puckered Cu–O planes than the Ca-free (Hg 0.5Tb 0.5)Sr 2TbCu 2O 6+ δ phase. Syperconductivity is observed only for samples with x>0.2 and T c increases with increasing Ca content, x. The results of thermoelectric power measurements suggest that the samples with x<0.8 are located in the underdoped region and the x=0.8 sample is optimally doped and exhibits the highest T c of 88 K.