Transport measurements in the 1-2-3 system CLBLCO in both the oxygen-underdoped and -overdoped regions

"CLBLCO" is a family of 1-2-3 superconductors, represented by the chemical formula (CaxLa1-x)(Bac-xLa2-c+x)Cu3Oy. By annealing in oxygen at various pr essures, up to 4300 bar, at a temperature of 300 degrees C and above, we ha ve prepared specimens whose oxygen content covers a wide range, from y = 6. 4 (a totally "underdoped" insulating phase) to a highly overdoped phase wit h y greater than or similar to 7.354. In contrast to YBCO, the specimens re main tetragonal for all values of x, c, and y. Measurements of the supercon ducting transition temperature, the resistivity, and the thermoelectric pow er, over a range of y values, 6.84 less than or equal to y less than or equ al to 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 prop erties of the underdoped and overdoped regimes. In contrast to YBCO, the th ermoelectric power characteristics behave like those of most other high-ir, cuprates. We found that a proposed universal relation between the thermoel ectric power and the ratio between T-c and its maximum value T-c,T-max is n ot truly universal; it holds in some cases, but fails in others. The temper ature-dependence of the resistivity shows a departure from linearity in the overdoped region, which is perhaps the signature of the appearance of a no rmal-state gap. The temperature at which the non-linearity sets in appears to increase as the doping level falls. (C) 1999 Elsevier Science B.V. All r ights reserved.