Relationship between the lattice parameter and superconductivity in the 2-1-4 series n-type cuprates
- National Laboratory for Superconductivity, Institute of Physics, and the Center of Condensed Matter Physics, Chinese Academy of Sciences, Beijing, 100080, Peoples Republic of (China)
- National Laboratory for Superconductivity, Institute of Physics, and the Center of Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100080, Peoples Republic of (China)
- Department of Physical Chemistry, University of Science and Technology Beijing, Beijing, 100083, Peoples Republic of (China)
The superconductivity of R{sub 2{minus}x{minus}y}La{sub y}Ce{sub x}CuO{sub 4{minus}{delta}} (R=Nd, Gd, y=0, 0.2, 0.5,{hor_ellipsis}, 1.4. x=0.10,{hor_ellipsis}, 0.15,{hor_ellipsis}, 0.25) series are studied. The solubility limit of La{sup 3+} in Nd{sub 1.85{minus}y}La{sub y}Ce{sub 0.15}CuO{sub 4{minus}{delta}} is determined to be y{sub lim}=1.3, while the Ce-solubility limit increases to X{sub lim}=0.25 in Nd{sub 0.7{minus}x}La{sub 1.3}Ce{sub x}CuO{sub 4{minus}{delta}} with the maximum lattice parameter a=3.995 {Angstrom}. The T{sub c}{sup on} and the bulk superconducting fraction are found to decrease with increasing La content. However, the reduction of superconductivity induced by increasing lattice constant a can be compensated by a proper decrease of Ce content irrespective of the lattice parameter a up to 3.982 {Angstrom}. These results indicate that the lattice parameters are not directly related to the superconductivity. Actually, both the change of the a parameter and the Ce content x induce a variation in oxygen vacancies {delta} and result in the change of the charge-carrier density. Taking these facts into account, we give a simplified formula to calculate the charge-carrier density n{sub 0} as n{sub 0}=x+2{delta}=x+2(Aa+Bx+C{sub 0}). In order to keep an optimum charge-carrier density for superconductivity, the variations in oxygen vacancies induced by the change of lattice parameter a must be compensated by an appropriate decrease of Ce dopant. This implies that the a parameter, doping concentration, oxygen vacancy, and the charge-carrier density can be taken into unified consideration, in which the charge-carrier density is considered to be a determining factor for superconductivity. {copyright} {ital 1997} {ital The American Physical Society}
- OSTI ID:
- 450394
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 55, Issue 6; Other Information: PBD: Feb 1997
- Country of Publication:
- United States
- Language:
- English
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