Study on Ca-doping effects and structural stability in Bi2Sr2-xCaxCuO6+δ (0 ≤ x ≤ 1.2) compounds by Rietveld refinement and high-pressure Raman spectroscopy.

The lattice distortion induced by element doping is regarded as an effective approach to improve the superconductivity of Bi-based superconductors. In this study, a series of Bi 2 Sr 2- x Ca x CuO 6+ δ (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 and 1.2) ceramic samples are prepared by Pechini sol-gel method. The Ca-doping effects, structural stability and superconductivity of Bi-2201 phase are studied by electron microscopy, high-pressure Raman spectroscopy, the standard four-probe technique, X-ray diffraction and Rietveld refinements. Results indicate that all samples are constituted by Bi-2201 main phase and Ca 8.56 Sr 5.44 Bi 16 O 38 impurity. It can be determined that Ca atoms have entered Bi-2201 orthorhombic lattice and preferentially occupied the Sr-sites. When Ca atoms are introduced and high-pressure is exerted, the Bi-2201 lattice can present a relatively high structural stability. Meanwhile, the correlations between doping amount x , Cu–O–Cu bond angle (θ), carrier concentration of CuO 2 planes and superconducting onset transition temperature (T c,onset) are discussed particularly. It should be noted that the Bi-2201 lattice has the largest θ , the highest carrier concentration and the highest T c,onset value of 84.98 K when x = 0.8. [ABSTRACT FROM AUTHOR]