Phase separation and oxygen diffusion in electrochemically oxidized La2CuO4+delta: A static magnetic susceptibility study

被引:62
作者
Chou, FC
Johnston, DC
机构
[1] IOWA STATE UNIV SCI & TECHNOL, AMES LAB, AMES, IA 50011 USA
[2] IOWA STATE UNIV SCI & TECHNOL, DEPT PHYS & ASTRON, AMES, IA 50011 USA
关键词
D O I
10.1103/PhysRevB.54.572
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
The compound La2CuO4+delta is known to phase separate for 0.01 less than or similar to delta less than or similar to 0.06 below a temperature T-ps similar to 300 K into the nearly stoichiometric antiferromagnetic compound La2CuO4.01-4.02 with Neel temperature T-N similar to 250 K, and a metallic oxygen-rich phase La2CuOsimilar to 4.06 with superconducting transition temperature T-c approximate to 34 K. We report studies of the superconducting and normal-state static magnetic susceptibility chi of La2CuO4+delta samples with 0 less than or similar to delta less than or equal to 0.11 prepared by electrochemical oxidation or reduction of conventionally synthesized ceramic La2CuO4+delta. The upper limit to the miscibility gap at low T is found be delta less than or similar to 0.065, in agreement with the previous work. The interstitial oxygen diffusion during the phase-separation process was studied using thermal- and magnetic-field history-dependent chi(T,t) measurements versus temperature T and time t as a probe. Phase-separation is found to be suppressed by quenching at greater than or similar to = 100 K/s and favored by slow cooling at similar to 0.5 K/min. A large thermal hysteresis of both the normal and superconducting state chi(T) was observed between data obtained after quenching to 5 K and then warming, and data obtained while or after slowly cooling from 300 K, for samples of La2CuO4+delta (delta approximate to 0.030, 0.044) within the miscibility gap. Quenching reduces T-c by approximate to 5 K relative to the value (34 K) obtained after slow cooling. A similar decrease is found for La2CuO4.065 which does not phase separate, indicating the importance of oxygen-ordering effects within this single phase. A model for the excess oxygen diffusion is presented, from which the data yield a nearly T-independent activation energy for excess oxygen diffusion of (0.24 +/- 0.03) eV from 150 to 220 K apart from a possible anomaly near 210 K.
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页码:572 / 583
页数:12
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