OPTICAL INVESTIGATION OF THE VALENCY OF PR IN Y1-XPRXBA2CU3O7-DELTA

We have investigated the dependence of the visible-ultraviolet dielectric function of Y(1-x)Pr(x)Ba2Cu3O7 On the Pr content x using rotating analyzer ellipsometry. Based on recently published band-structure calculations, we believe that the valency of Pr can be deduced from the optical properties in this spectral region. Interband transitions should shift to higher energies for Pr4+ and to lower energies for Pr3+ when compared to the optical spectra of YBa2Cu3O7. In the case of tetravalent Pr ions, transitions into unoccupied Pr 5d levels should be observable. Since the experimental energies for interband transitions shift down with increasing x and no additional structure can be seen, we conclude that Pr is trivalent in Y(1-x)Pr(x)Ba2Cu3O7.