Investigation on incommensurate modulation structure and Tc in Ca-doped Bi-2201 system

Abstract A series of samples with the nominal composition of Bi 2 Sr 2− x Ca x CuO 6+ δ ( x  = 0.2, 0.4, 0.6, 0.8, 1.0) ceramics are synthesized by sol–gel growth. The microstructure and the incommensurate modulation structure (IMS) were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. The superconductivity and the onset temperature of superconducting transition ( T c,onset ) were analysed. In the whole Ca-doping range, an IMS in b ∗ –c ∗ planes can be identified and the values of T c,onset are all exceed 80 K. With an increase of x , the b -component of modulation vector q ∗ , the basic structural parameters b and c of Bi-2201 phase have a trend of fall first then rise, whereas the c -component of modulation vector, the angle θ between q ∗ and b ∗ vectors and the values of T c,onset are reversely varied. It can be verified that Ca concentration x  = 0.6 is an extreme value, at which the distortion of the CuO 2 layers makes the concentration of mobile carriers and the value of T c,onset optimizing.