MOSSBAUER STUDY OF EFFECT OF SUBSTITUTION OF PR IN EU-CONTAINING HIGH-TEMPERATURE SUPERCONDUCTOR

Eu1-xPrxBa2Cu3O7-d(0 less than or equal to x less than or equal to 1) and EuBa1.5Pr0.5Cu3O7-d samples have been investigated by means of(151 )Eu Mossbauer spectroscopy, X-ray diffractometry and electrical resist ivity measurements. Changes in the electrical resistivity, in the unit cell volume and in the electronic density as well as in the electric field gradient at the site of the (151)EU nucleus have been found as a function of Pr content. These changes can be attributed to the occurr ence of Pr with a valence state higher than +3. The suppression of sup erconductivity can be explained by hole filling of extra electrons of Pr in the CuO2 plane. The strong differences between EuBa1.5Pr0.5Cu3O7 -d and Eu0.5Pr0.5Ba2Cu3O7-d can indicate that the Pr can be substitute d not only for the Eu, but also for the Pa site.