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自La-Ba(Sr)-Cu-O高温超导体发现以来,已经得到了许多含铜的氧化物超导体,这些超导体中都含有一个Cu以八面体或四方锥配位的CuO_2平面,载流子是空穴。1989年初日本Tokura等人首先发现了电子型超导体(Ln_(1.85)Ce_(0.15))CuO_(4-y),Ln=Pr,Nd,Sm。相继报导了这一系列的其他几个超导体:(Pr_(1.85)Th_(0.15))CuO_(4-y)和(Eu_(1.85)Ce_(0.15))CuO_(4-y)(Nd_(1.85)Th_(0.15))CuO_(4-y),Nd_2CuO_(4-y)Fy。这类超导体的Tc都在20K左右,载流子是电子,CuO_2面内的Cu为四方形配位。将这一类超导体的结构称为T′相结构,相应地称K_2NiF_4型的La_(2-x)Sr_xCuO_4的结构为T相结构。两种晶体结构示于图1。两年多来,寻找更高T_c的电子型超导体是超导界所关心的问题之一,具
Since the discovery of La-Ba (Sr) -Cu-O high-temperature superconductors, many copper-containing oxide superconductors have been obtained. All these superconductors contain a CuO 2 plane with Cu coordinated by octahedron or tetragon. The carriers are Hole. At the beginning of 1989, Tokura et al. First discovered the electronic superconductor (Ln_ (1.85) Ce_ (0.15)) CuO_ (4-y), Ln = Pr, Nd and Sm. (Pr_ (1.85) Th_ (0.15)) CuO_ (4-y) and (Eu_ (1.85) Ce_ (0.15)) CuO_ (4-y) Nd_ (1.85) have been reported one after another in this series. Th_ (0.15)) CuO_ (4-y), Nd_2CuO_ (4-y) Fy. These superconductors Tc are about 20K, carriers are electrons, CuO_2 CuO within the plane of the square coordination. The structure of this type of superconductor is called T ’phase structure. Correspondingly, the structure of K 2 NiF 4 -type La 2-x Sr x CuO 4 is T phase structure. The two crystal structures are shown in FIG. 1. For more than two years, looking for higher Tc electronic superconductors is one of the concerns of the superconductor industry, with