A New Superconducting Phase of Sodium Cobalt Oxide
A New Superconducting Phase of Sodium Cobalt Oxide
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DOI：
10.1002/adma.200400756
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发表时间：
2004-11
影响因子：
29.4
通讯作者：
K. Takada;H. Sakurai;E. Takayama-Muromachi;F. Izumi;R. Dilanian;T. Sasaki
中科院分区：
文献类型：
--
作者：
K. Takada;H. Sakurai;E. Takayama-Muromachi;F. Izumi;R. Dilanian;T. Sasaki
最近，我们发现了第一个超导钴氧化物系统。[1]超导钴氧化物和高温(TC)铜氧化物的异同可能有助于解释高温超导电性的起源。[2]一些文献指出，所讨论的钴氧化物可能是长期以来一直被追寻的共振价键(RVB)超导体。[3]人们开始了深入的研究，但大多数是理论[4]和实验[5]的努力，以阐明超导机制；到目前为止，还没有在钴氧化物系统中发现其他超导体。对相关超导相的研究将有助于加深对超导电性的理解。在本文中，我们报道了这样一个相--氧化钴钠的一种新的超导相。新相由厚的Na+和H2O(H3O+)绝缘层隔开的CoO2层组成，扩展的层间距为9.8。这些结构特征与以前报道的超导相相似。[1]然而，CoO2层的堆积顺序不同：本材料中的CoO2层具有三层周期，而超导相中的CoO2层具有两层周期。新相在4.6K时出现超导转变。第一个超导体是从母体层状氧化物γ-NaO中获得的。7CoO2，[6，7]通过软化学修饰。无水的γ-Na0。7CoO2经Br2处理后用水洗后转变为双分子水合物(BLH)相。层状三元氧化物体系，包括母体氧化物，通式为AxMo2(A：碱金属，M：过渡金属)，属于-
Recently, we discovered the first superconducting cobalt oxide system.[1] Similarities and differences between the superconducting cobalt oxide and high-transition-temperature (Tc) copper oxides may shed light on the origin of high-Tc superconductivity, which has eluded explanation for more than 15 years.[2] Some papers have pointed out that the cobalt oxide in question may be the resonating valence bond (RVB) superconductor that has long been sought after.[3] Intensive studies have been stimulated, but most of them have been theoretical [4] and experimental [5] efforts to elucidate the superconducting mechanism; no other superconductors have been found in the cobalt oxide system so far. Studies on related superconducting phases should be very helpful in obtaining a deeper understanding of superconductivity. In the present paper we report on such a phase, a new superconducting phase of sodium cobalt oxide. The new phase consists of CoO2 layers separated by thick insulating layers of Na+ and H2O (H3O+), giving an expanded interlayer distance of 9.8. These structural features are similar to those of the previously reported superconducting phase.[1] However, the stacking sequence of the CoO2 layers is different: the CoO2 layers in the present material have a three-layer periodicity, in contrast to the two-layer one in the superconducting phase already reported. The new phase showed a superconducting transition at 4.6 K.The first superconductor of sodium cobalt oxide was obtained from a parent layered oxide, γ-Na0. 7CoO2,[6, 7] through soft-chemical modification. The anhydrous γ-Na0. 7CoO2 was transformed into a bilayer-hydrate (BLH) phase via treatment with Br2, followed by washing with water. Layered ternary oxide systems, including the parent oxide, with general formula AxMO2 (A: alkali metal, M: transition metal) are categor-