Erno Kuzmann

Evidence for Pr3+ in EuBa1.3Pr0.7Cu3O7-δ by 141Pr Mössbauer spectroscopy

Abstract The polycrystalline compound EuBa 1.3 Pr 0.7 Cu 3 O 7− δ has been prepared and investigated by the means of 141 Pr Mossbauer spectroscopy. The observed 141 Pr Mossbauer isomer shift, δ (at T =4.2 K)=0.10 (15) mm/s relative to PrF 3 , reflect a valence state of 3+ for Pr located at the Ba site in EuBa 1.3 Pr 0.7 Cu 3 O 7− δ . Magnetic order of the Pr sublattice was not observed at T =4.2 K in contrast with the compound Eu 0.3 Pr 0.7 Ba 2 Cu 3 O 7− δ where magnetic order of the Pr sublattice appears at T =12 K. Our results explain why Pr behaves very similar to other 3+ cations (La, Nd) when substituted for Ba in this system, and suggests that suppression of superconductivity by Pr substituted at the rare earth site is a consequence of the hole filling effect.

Structural Investigation of the Effect of Praseodymium in Eu1-xPrxBa2Cu3O7-δ and EuBa2-xPrxCu3O7-δ Perovskites by 151Eu and 141Pr Mössbauer Spectroscopy

Abstract151Eu and 141Pr Mössbauer spectroscopy was applied to study the effects of Pr substitution for Eu or Ba atoms in Eu1-xPrxBa2Cu3O7-δ and EuBa2-xPrxCu3O7-δ, respectively. It was found that there exists a correlation between the 151Eu isomer shift and the onset temperature of the superconducting transition, independent of the location of Pr. This shows that the extra electrons provided by the Pr increase the electronic density in the copper oxide planes and in the 4f orbitals of Eu31, simultaneously. The polycrystalline compound EuBa1.3Pr0.7Cu3O7-δ has been investigated by 141Pr Mössbauer spectroscopy. The observed 141Pr isomer shift, δ(4.2 K) = 0.10(15) mm/s relative to PrF3, reflects a valence state of 3+ for the Pr located at the Ba site in EuBa1.3Pr0.7Cu3O7-δ, being in contrast to the valence state of 3.4+ found earlier for Pr which was situated at the rare earth site. This means that the valence state of Pr substituted for Eu is different from that of Pr substituted for Ba. These results suggest that the suppression of superconductivity by Pr substituted for the rare earth atoms is a consequence of the hole filling effect.

151Eu Mössbauer study of Eu3C60

Abstract Eu 3 C 60 salt was synthesized via the liquid ammonia route. X-ray diffractometry data show the formation of a single phase material with lattice parameters close to Eu 3 C 60 prepared previously by solid state reaction. A detailed study of 151 Eu Mossbauer spectroscopy of Eu 3 C 60 salt is presented. It was found that the relative occurrence of Eu 2+ and Eu 3+ cations is equal to 4:1.

Mössbauer and X-ray Investigation of Clay Minerals Originated from Libya

Abstract57Fe transmission Mössbauer spectroscopy and X-ray diffractometry were used to study clay mineral samples originated from two different regions (Um-arrazm and Alkawasim) of Libya in order to get information about their mineralogical composition to assess their potential for use in the Libyan oil industry. In the samples originated from Um-arrazm calcite, akaganeite and nontronite while in the samples originated from Alkawasim quartz, akaganeite, montmorillonite, kaolinite, illite, mica and hematite were identified with different ratios by using diffraction method. The differences in the phase composition of iron-containing phases of samples from different localities have reflected in the complex Mössbauer spectra at both 300 K and 80 K. For the samples originated from Um-arrazm the Mössbauer parameters of subspectra were identified as nontronite and akaganeite.

Nuclear Techniques in the Elucidation of Chemical Structure

The paper offers three applications of nuclear methods in the research of chemical structure. First, progress in positron annihilation spectroscopy is illustrated by a positron beamline study, which obtained results that are not available through conventional experiments. The positron beam was used for the study of Langmuir-Blodgett (LB) films containing 4-58 layers of arachidic acid and its salts. These measurements have shown that this emerging technique is capable of characterizing even such elusive systems. Second, the potential of Mössbauer spectroscopy to answer current challenges of solid state chemistry are shown in a study on perovskites of recent interest. 151Eu Mössbauer spectroscopy was used to study the effect of Pr substitution in EuBa2Cu3O7-δ. It was shown that the introduction of Pr into the rare earth site as well as into the Ba site results in the appearance of extra electrons both in the copper oxide planes and at the 4f shell of Eu cations. The observed effects were explained by the hole filling effect of Pr. Finally, a survey is presented on the recently developed techniques for nuclear resonant scattering of synchrotron radiation, an exciting and very rapidly developing extension to conventional Mössbauer spectroscopy. An interesting new result is that nuclear inelastic scattering experiments performed on solutions of 57Fe complexes show contribution from vibrations rather than from diffusion to the inelastic spectra.