Superconductivity at 40 K in La1.8Sr0.2CuO4 |
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Authors: | C Politis J Geerk M Dietrich B Obst |
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Institution: | (1) Institut für Nukleare Festkörperphysik, Kernforschungszentrum Karlsruhe, Postfach 3640, D-7500 Karlsruhe, Federal Republic of Germany;(2) Institut für Technische Physik, Kernforschungszentrum Karlsruhe, Postfach 3640, D-7500 Karlsruhe, Federal Republic of Germany |
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Abstract: | High-T
c superconductivity withT
c onsets up to 42 K (midpoint: 37 K, zero resistance: 34 K) is observed in X-rays homogeneous single phase La1.8Sr0.2CuO4. The quarternary compounds La2–x
Ba
x
CuO4 and La2–x
Sr
x
CuO4 (0x0.3 for Ba and 0x<1 for Sr, depending on the heating conditions) are mixed-valence oxygen defect oxides, characterized by the presence of Cu2+ and Cu3+ simultaneously. These oxides have a tetragonal symmetry (space group:I 4/mmm) similar to that of K2NiF4. We report the synthesis, characterization, and superconducting properties of various high-temperature superconducting La–Ba–Cu–O and La–Sr–Cu–O compounds. Through the substitution of Sr for Ba in these oxygen defect compounds an increasing superconducting transition temperature onset from 28 K to 35 K for La1.8Sr0.1Ba0.1CuO4 was observed. A positive initial pressure coefficient ofdTc/dp=290 (mK/kbar) has been found for La1.8Sr0.2CuO4 with a magnetic susceptibility change consistent with the 100% diamagnetic expectation value. |
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Keywords: | |
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