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

本文研究了R_ Pr_xBa_2Cu_3O_（R为Nd，Gd，Ho，Y和Yb）中不同氧浓度时，Pr含量x对超导转变温度Tc的影响<1-x><7-y>。对于R*Nd，其离子半径小于Pr的情况，Pr取代Tc的初始降低速率（-dTc/dx）在6.6&lt;7-y&lt;7.0时随氧浓度的降低而减小，在7-y&lt;6.6时则趋于常数。重掺Pr区的-dTc/dx比初始区的大，与R=Nd时一致。与此相反，在R=Nd的情况下，其离子半径几乎与Pr的相同，-dTc/dx不仅不依赖于氧浓度，而且Pr含量。通过考虑空穴从Cu（1）O链到Cu（2）O_2平面的转移，解释了在R*Nd的情况下Pr对Tc抑制的减弱。认为空穴从Cu（1）O链向Cu（2）O_2面的转移是由于大Pr离子取代小Y离子位置，导致顶点氧位置的局部畸变所致。Pr置换的空穴迁移与氧缺位的空穴迁移相似，但迁移方向相反。

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.