Superconductivity in the triple-perovskite La-Ca-Ba-Cu-O system
Y F Yang; D S Wu; H -C I Kao; C M Wang; M K Wu; Y F Yang; Dept. of Chem., Tamkang Univ., Tamsui, Taiwan; D S Wu; Dept. of Chem., Tamkang Univ., Tamsui, Taiwan; H -C I Kao; Dept. of Chem., Tamkang Univ., Tamsui, Taiwan; C M Wang; Dept. of Chem., Tamkang Univ., Tamsui, Taiwan; M K Wu; Dept. of Chem., Tamkang Univ., Tamsui, Taiwan
Журнал:
Superconductor Science and Technology
Дата:
1995-12-01
Аннотация:
Three series of single-phase La-Ca-Ba-Cu-O compounds with tetragonal triple-perovskite structure and respective nominal compositions of La<sub>4-x</sub>Ca<sub>x</sub>Ba<sub>3</sub>Cu<sub>7</sub>O<sub>y</sub> (LC series, 0.50<or=x<or=1.15), La<sub>3</sub>Ca<sub>x</sub>Ba<sub>4-x</sub>Cu<sub>7</sub>O<sub>y</sub> (CB series, 0<or=x<or=1.25) and La<sub>3.5-0.5x</sub>Ca<sub>x</sub>Ba<sub>3.5-0.5x</sub>Cu<sub>7</sub>O<sub>y</sub> (LCB series, 0<or=x<or=1.25) were prepared by either a solid state reaction method or a polymeric citrate precursor method. All the single-phase materials were superconducting except for samples containing small x in the LCB series. Unit-cell parameters, such as a axes, c axes and cell volume, decreased with increasing Ca substitution. In general, the T<sub>c</sub> and hole concentration (p) increased with increasing x from x=0 to x=1.00. In other words, evidence of hole doping was observed during Ca substitution that was the main reason for the increase of the T<sub>c</sub> from 0 to 80 K. The optimal T<sub>c</sub> was observed in a region close to the formula of La<sub>3</sub>CaBa<sub>3</sub>Cu<sub>7</sub>O<sub>y</sub> which had a formula per unit celt of La<sub>1.29</sub>Ca<sub>0.43</sub>Ba<sub>1.29</sub>Cu<sub>3</sub>O<sub>z</sub> where z=7.104, p=0.308, a axis =0.3879 nm and T<sub>c(zero)</sub>=80 K.
298.7Кб