摘要
To interpret the metal-insulator transition and depression of Tc induced by Pr-and Ce-doping in YBa_2Cu_3O_7, we propose a model of mixed local hole states which describe a strong admixture of 4f^1 state with states of 4f^2 plus a hole in the CuO_2 planes for Y_(1-x)-Pr_x-0_7 and 4f^0 state with states of 4f^1 plus a hole in Y_(1-x)Ce_x-O_7. Our model resolves the controversy between the magnetic and spectroscopic measurements. As a natural consequence, most of the experimental results on Y_(1-x)Pr_x-O_7 can be explained and certain properties of Y_(1-x)Ce_x-O_7 are predicted. The critical doping density of Pr will take the value of x_c ≈0.5.
To interpret the metal-insulator transition and depression of Tc induced by Pr-and Ce-doping in YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub>, we propose a model of mixed local hole states which describe a strong admixture of 4f<sup>1</sup> state with states of 4f<sup>2</sup> plus a hole in the CuO<sub>2</sub> planes for Y<sub>1-x</sub>-Pr<sub>x</sub>-0<sub>7</sub> and 4f<sup>0</sup> state with states of 4f<sup>1</sup> plus a hole in Y<sub>1-x</sub>Ce<sub>x</sub>-O<sub>7</sub>. Our model resolves the controversy between the magnetic and spectroscopic measurements. As a natural consequence, most of the experimental results on Y<sub>1-x</sub>Pr<sub>x</sub>-O<sub>7</sub> can be explained and certain properties of Y<sub>1-x</sub>Ce<sub>x</sub>-O<sub>7</sub> are predicted. The critical doping density of Pr will take the value of x<sub>c</sub> ≈0.5.
