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Effect of Hf and HfCa substitution on the superconductivity of ErBa2Cu3O7−δ

Physica C Superconductivity
Publication Date
DOI: 10.1016/0921-4534(96)00142-6
  • Physics


Abstract The structural and superconducting properties of (Er 1− y−y Ca y Hf x )Ba 2Cu 3O z samples are investigated using X-ray diffraction, resistivity, AC susceptibility and oxygen-content measurements. The effect of increasing the Hf concentration in Er − x Hf x Ba 2Cu 3O z lowers the oxygen content and decreases T c which is attributed to hole filling by Hf. The substitution of Ca for Er in (Er 0.85− y Ca y Hf 0.15)Ba 2Cu 3O z provides a proper matching between the ionic radius and valence of Er 3+ (0.88 Å) and the average ionic radius and valence of Hf 4+ (0.78 Å) and Ca 2+ (0.99 Å). As the Ca content increases, the T c increases from 70 K ( y = 0.05) to 86 K ( y = 0.25, compensated oxide), closer the value of 91 K for pure ErBa 2Cu 3O 7−δ due to the balance between the hole filling by Hf and hole doping by Ca.

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