ANALYSIS OF THE POSSIBLE REASONS FOR THE SUPPRESSION OF SUPERCONDUCTIVITY IN THE Y1-XPRXBA2CU3OY SYSTEM ON THE BASIS OF THERMOELECTRIC-POWER DATA

The temperature dependence of the thermoelectric power in samples of Y 1-xPrxBa2Cu3Oy (x=0-0.6) is investigated. The principal parameters of the system of charge carriers are determined on the basis of an analys is of this dependence within a narrow-conduction-band model, and their variation with increasing praseodymium content is analyzed, It is fou nd that an increase in x leads to a very weak increase in the electron filling and considerable broadening of the conduction band accompanie d by strong localization of the charge carriers. It is concluded on th e basis of a comparative analysis of the results obtained and data for the YBa2Cu3Oy system in the case of aliovalent substitutions in the b arium and copper sites that the valence of praseodymium in Y1-xPrxBa2C u3Oy is very close to 3+, It is shown that then is a universal correla tion between the effective width of the conduction band and the critic al temperature following various cation substitutions in the Y-Ba-Cu-O system, It is concluded that the main reason for suppression of the s uperconducting properties of Y1-xPrxBa2Cu3Oy is the strong modificatio n of the band spectrum caused by praseodymium. (C) 1997 American Insti tute of Physics.