Oxygen Concentration Dependence of Pr-Suppression Effect on Superconductivity in (123) Phase Oxide Superconductor

在R_<1-x>Pr_xBa_2Cu_3O_<7-y>中，R为Nd， Gd, Ho， Y和Yb，研究了不同氧浓度下，Pr含量与超导转变温度Tc的关系。在R*Nd离子半径小于Pr的情况下，当氧浓度为6.6<7-y<7.0时，Pr取代Tc的初始降低速率（-dTc/dx）随氧浓度的降低而减小，当7-y<6.6时保持不变。重掺pr区域的-dTc/dx大于初始区域，与R=Nd时的-dTc/dx一致。相反，当R=Nd时，离子半径与Pr几乎相同，其-dTc/dx不仅与氧浓度无关，而且与Pr含量无关。考虑Cu (1) O链到Cu (2) O_2平面的空穴转移，可以解释R*Nd中Pr对tc抑制的减弱。从Cu (1) O链到Cu (2) O_2平面的空穴转移被认为是由于大的Pr离子取代了小的Y离子而引起的顶端氧位置的局部变形所致。Pr取代的空穴转移与缺氧的空穴转移相似，但转移方向相反。

The Pr content x dependence of the superconducting transition temperature Tc is examined for various oxygen concentrations in R_<1-x>Pr_xBa_2Cu_3O_<7-y>, where R is Nd, Gd, Ho, Y and Yb. In the case of R*Nd, ionic radii of which are smaller than that of Pr, the initial rates of decrease of Tc by Pr substitution (-dTc/dx) decrease with decreasing oxygen concentration for 6.6<7-y<7.0, then becomes constant for 7-y<6.6. The -dTc/dx in the heavily Pr-doped region is larger than that in the initial one, and coinsides wiht that in the case of R=Nd. In contrast, the -dTc/dx in the case of R=Nd, ion radius of which is nearly the same as that of Pr, does not depend upon not only the oxygen concentration but also the Pr content. The weakened Tc-suppression by Pr in the case of R*Nd is explained by considering the hole transfer from the Cu (1) O chain to the Cu (2) O_2 plane. The hole transfer from the Cu (1) O chain to the Cu (2) O_2 plane is caunsidered to be caused by the local distortion in the position of apical oxygen on accout of the substitution of large Pr ion to the small Y ion site. This hole transfer by Pr substitution is similar to that by oxygen deficiency, but the direction of transfer is the opposite with each other.