Ca effect on the normal-state and superconducting properties of Y-based HTS

Characterization and synthesis of Y0.9Ca0.1Ba1.8Sr0.2Cu3O7−δ via combining sol–gel and solid-state route

“…The lattice distortion is contributed by the difference of ionic radii between the doping element with the native element. Many reports [4][5][6][7][8][9][10] show that with fixed oxygen stoichiometry, the substitution of Ca for Y generates holes at CuO 2 planes which has influence over superconducting transition temperature without changing the crystal structure of the sample due to slightly difference between the ionic radii. However, it was found that oxygen vacancies (which fill holes) are always cointroduced with Ca, thus reducing its holes generation effect [4].…”

“…Ca 2+ valence is smaller than the one of the substituted Y 3+ that can result in increasing number of hole [6][7][8][9][10][11]. Anyway, increasing Ca content to replace Y in Y-123 phase was found to be accompanied by decreasing oxygen content [4][5][6][7][8][9][10][11]. According to Awana et al [11] on replacement of Y by Ca, the oxygen content of Y 1Àx Ca x Ba 2 Cu 3 O 7Ày (y % 0.3) system remains nearly unchanged, till x = 0.1 and drops sharply to x = 0.15, which is followed by decreasing bond distances Cu-O planes with increasing Cu(2)-O(2)-Cu(2) angle.…”

“…Many researchers [5][6][7][8][9] have long attempted the substitution of Ca for Y in Y-123. Ca-doped YBCO is particularly of interest in the study of the electronic properties of CuO 2 planes and the C-O chains.…”

On the transformation of the normal-state band spectrum of Tl-based HTSC’s with increasing number of CuO2 layers and doping level

“…As shown in our previous publications, this model, based on the assumption of the existence of a narrow density-of-states (DOS) peak in the band structure of HTSC-materials, allows one to describe all the features of the normal-state transport properties of yttrium-, lanthanum-, bismuth-and mercurybased superconductors [8][9][10]15,[19][20][21][22]. In the framework of this model, approximating the DOS D(e) and the differential conductivity, r(e), functions by rectangles of different widths, one can obtain analytical expressions for the chemical potential, l, and the transport coefficients.…”

Mechanism of a strong rise of T due to the calcium doping in Y1−Ca Ba2Cu2.8Zn0.2O

“…The specific effect of calcium doping is the ability of this impurity to restore the superconductivity suppressed by some other factors [4][5][6][7][8]. For example, additional Ca doping in Y 1Àx Ca x Ba 2Àz La z Cu 3 O y and Y 1Àx Ca x Ba 2 Cu 3Àz Co z O y with fixed La or Co content results in T c increase or even the superconductivity restoration [4,5,7,8]. This effect is related to the fact that all the properties of the above systems were preliminary changed by the first dopant with a valence higher than the substituted cation one [5][6][7][8].…”