Effect of Cu-Ga and coupled Nd-Ca/Cu-Ga substitution on the superconductivity of NdBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub>
Amish G Joshi; R G Kulkarni; Amish G Joshi; Department of Physics, Saurashtra University, Rajkot-360 005, India; R G Kulkarni; Department of Physics, Saurashtra University, Rajkot-360 005, India
Журнал:
Superconductor Science and Technology
Дата:
2000-08-01
Аннотация:
The structural and superconducting properties of (Nd<sub>1-y</sub>Ca<sub>y</sub>)Ba<sub>2</sub>(Cu<sub>1-x</sub>Ga<sub>x</sub>)<sub>3</sub>O<sub>z</sub> samples have been studied by x-ray diffraction, resistivity, ac susceptibility and oxygen content measurements. The effect of increasing the Ga concentration in NdBa<sub>2</sub>(Cu<sub>1-x</sub>Ga<sub>x</sub>)<sub>3</sub>O<sub>z</sub> reduces the orthorhombicity without much disturbing the oxygen-vacancy order. This is accompanied by an increase in the normal state resistivity and decreases in both the carrier concentration and T<sub>c</sub>, which is attributed to hole filling by Ga. This suppression of T<sub>c</sub> has been compensated by appropriate hole doping with Ca in (Nd<sub>1-y</sub>Ca<sub>y</sub>)Ba<sub>2</sub>(Cu<sub>1-x</sub>Ga<sub>x</sub>)<sub>3</sub>O<sub>z</sub>, which shows that for a fixed Ga content T<sub>c</sub> increases dramatically as the Ca content increases. For instance, in the oxide (Nd<sub>1-y</sub>Ca<sub>y</sub>)Ba<sub>2</sub>(Cu<sub>0.94</sub>Ga<sub>0.06</sub>)<sub>3</sub>O<sub>z</sub>, the T<sub>c</sub> increases from 0 K (y = 0.0, semiconductor) to 76 K (y = 0.36, compensated oxide) as the hole filling by Ga is nearly balanced by hole doping from Ca.
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