Transport measurements in the 1-2-3 system CLBLCO in both the oxygen-underdoped and -overdoped regions
| Autor: | George M. Reisner, Y Direktovich, A. Knizhnik, D. Goldschmidt, C. G. Kuper, Y. Eckstein |
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| Rok vydání: | 1999 |
| Předmět: |
Superconductivity
Materials science Condensed matter physics Transition temperature Doping Energy Engineering and Power Technology Condensed Matter Physics Electronic Optical and Magnetic Materials Tetragonal crystal system Impurity Electrical resistivity and conductivity Seebeck coefficient Cuprate Electrical and Electronic Engineering |
| Zdroj: | Physica C: Superconductivity. 321:199-206 |
| ISSN: | 0921-4534 |
| DOI: | 10.1016/s0921-4534(99)00363-9 |
| Popis: | “CLBLCO” is a family of 1-2-3 superconductors, represented by the chemical formula (Ca x La 1− x )(Ba c − x La 2− c + x )Cu 3 O y . By annealing in oxygen at various pressures, up to 4300 bar, at a temperature of 300°C and above, we have prepared specimens whose oxygen content covers a wide range, from y =6.4 (a totally “underdoped” insulating phase) to a highly overdoped phase with y ≳7.354. In contrast to YBCO, the specimens remain tetragonal for all values of x , c , and y . Measurements of the superconducting transition temperature, the resistivity, and the thermoelectric power, over a range of y values, 6.84≤ y ≤7.30 are presented, for samples with calcium content from x =0.1 to 0.4, and with c =1.75. We also report some transport data for CLBLCO with nickel impurities. Some significant differences were found between the properties of the underdoped and overdoped regimes. In contrast to YBCO, the thermoelectric power characteristics behave like those of most other high- T c cuprates. We found that a proposed universal relation between the thermoelectric power and the ratio between T c and its maximum value T c,max is not truly universal; it holds in some cases, but fails in others. The temperature-dependence of the resistivity shows a departure from linearity in the overdoped region, which is perhaps the signature of the appearance of a normal-state gap. The temperature at which the non-linearity sets in appears to increase as the doping level falls. |
| Databáze: | OpenAIRE |
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