Investigations on the Tl-doped Hg–Ba–Ca–Cu–O high temperature superconductors in regard to hole doping and microstructural characteristics

Abstract

The Tl-doped Hg-based HTSC bulk materials corresponding to Hg 1− x Tl x Ba 2Ca 2Cu 3O 8+ δ with x=0.2, 0.4, 0.5, 0.6, and 0.8 have been synthesized using the precursor route. A clear cut variation of T c( R=0) with increase in Tl concentration and hence from the underdoped to overdoped regions has been demonstrated. These variations correspond to T c variation from ∼106 to ∼133 K for underdoped samples and from ∼106 to ∼129 K for overdoped samples. The crossover from underdoped to overdoped regions is found to take place between x=0.5 and x=0.6 X-ray diffraction (XRD) and TEM studies have revealed the samples to be multiphasic with the presence of Hg, Tl:1223 as the dominant phase. Microstructural investigations reveal the presence of ordered and/or disordered stacking faults and the accompanying polytype like regions.