PRBA2CU3O7 INVESTIGATED BY PR-141 MOSSBAUER-SPECTROSCOPY

The Pr-141 Mossbauer isomer shift and hyperfine field of PrBa2Cu3O7 an d some other praseodymium oxides were measured. When we put the isomer shift of these oxides on a linear scale, we find for PrBa2Cu3O7 the m ean valency 3.4(1). This value corresponds to the number of holes whic h goes into the Pr-2(Cu(2)-O-2) layers. The spectra below T-N approxim ate to 17 K are broadened, but no well resolved hyperfine field split pattern is observed, We surmise that these spectra are due to relaxati on. In the discussion we ascribe the different results on the valency of Pr in PrBa2Cu3O7 reported in the literature to a different use of t he term valency, A model is furthermore proposed in which we suggest t hat the correlation of the Pr4f shell introduced into the O2p wave fun ctions is responsible for the anomalous properties of PrBa2Cu3O7.