Abstract
The oxygen content and the orthorhombicity of Y 0 . 7 C 0 . 3 Ba 2 Cu 3 O y F 0 . 2 are reduced compared to those of YBa 2 Cu 3 O y free samples. Further addition of fluorine decreases them more and more in Y 0 . 7 Ca 0 . 3 Ba 2 Cu 3 O y F 0 . 4 and reduces the superconducting volume fraction. As a consequence, Y 0 . 7 Ca 0 . 3 Ba 2 Cu 3 O y F 0 . 2 is optimally doped with charge carriers. On the contrary, Y 0 . 7 Ca 0 . 3 Ba 2 Cu 3 O y F 0 . 4 is underdoped. After an air-annealing at 450 °C and air quench, the normal state resistivity variation with temperature indicates the co-existence of weak metallic and semiconducting characters in both samples. An additional annealing in flowing oxygen at 920 °C makes Y 0 . 7 Ca 0 . 3 Ba 2 Cu 3 O y F 0 . 2 optimally doped with charge carriers while Y 0 . 7 Ca 0 . 3 Ba 2 Cu 3 O y F 0 . 4 , that becomes pseudo-tetragonal, is more underdoped than after preparation.
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