Y.Q. Jia

Electric field gradient at the Eu nucleus in EuBa2Cu3O7−x around the superconducting transition temperature

Abstract In Mossbauer effect studies of the superconductor EuBa 2 Cu 3 O 7− x an appreciable anomaly around the superconducting transition temperature in the variation of both the electric quadrupole splitting of the 151 Eu nucleus and the asymmetry parameter of the electric field gradient has been observed. The change in the electric field gradient components and the possible structural and electronic rearrangement in the Cu-O layers in the crystal in the process of superconducting transition is discussed.

CALCULATIONS OF THE EIGENVALUES OF PURE QUADRUPOLE INTERACTION IN MOSSBAUER-EFFECT STUDIES

SummaryTwo approximate formulae to calculate the eigenvalues of pure quadrupole interaction in Mössbauer effect studies have been proposed and the eigenvalue coefficients in the formulae have been given for various excited states and ground states of the nucleus with different spin. All the eigenvalues of pure quadrupole interaction between both excited state and ground state of nucleus with spinI=3/2÷9/2 and the electric-field gradient with different asymmetry parameter (η=0÷1.0) have been calculated by these formulae. The results show that the accuracies in all the calculations are more satisfactory or same in comparison with those obtained by the formula of Shenoy and Dunlap, especially when the asymmetry parameter of electric-field gradient is larger than 0.8 for the nucleus with spinI=5/2.

Mössbauer effect studies on some bioinorganic complexes of europium.

The bioinorganic complexes of europium with N-acetyl-DL-alanine, N-acetyl-DL-valine, and DL-alanyl-DL-alanine have been synthesized and the Mössbauer spectra at room temperature have been measured for these solid state complexes. The Mössbauer parameters indicate that the water molecules in these complexes are not directly linked to the central europium ion and are outside the coordination sphere of europium and biological ligands, and that the chemical bond between the europium ion and the ligands may be predominantly ionic in character, with the possibility of partial covalent contribution.

OBSERVATION OF MOSSBAUER-EFFECT IN THE HIGH-TEMPERATURE SUPERCONDUCTOR EUBA2CU3O7-X WITH DC ELECTRIC-CURRENT

The difference between the Mossbauer parameters for EuBa2Cu3O7-x with dc electric current and those without dc electric current at 83 K has been observed. The change in isomer shift, electric quadrupole splitting and the asymmetry parameter of the electric field gradient at the Eu-151 nucleus may be caused by the movement of a mass of conduction electrons along a certain direction in the EuBa2Cu3O7-x crystal with a layered structure.

PHOTOELECTRON-SPECTRA OF COMPLEXES OF NA AND LA WITH N-ACETYLALANINE AND N-ACETYLVALINE

X-ray photoelectron spectra of the bioinorganic complexes of Na and La with N-acetylalanine and N-acetylvaline have been measured. It has been found that the spectra of the O 1s core level in the complexes of Na with these amino acids are very different from those in the complexes of La with the same amino acids. The results indicate that in the complexes of La with N-acetylalanine and N-acetylvaline, both the oxygen atoms from the carboxyl group and the oxygen atoms from the carbonyl group of the amino acids will directly coordinate to the La ion, whereas only the oxygen atoms from the carboxyl group of the amino acids can directly coordinate to the Na ion in the complexes of Na with N-acetylalanine and N-acetylvaline.

Photoelectron spectra of various core levels in some rare earth N-acetylvaline bioinorganic complexes

X-ray photoelectron spectra of some bioinorganic complexes of La, Pr, Nd, Sm, and Gd with N-acetylvaline have-been measured. The complex formation does not give any detectable influence on the binding energy of the N 1s peak in the amino group, but has some appreciable effect on the binding energy of the C 1s peak and the O 1s peak in the carboxyl and carbonyl group of the biological ligand. The spin-orbit splitting between the 3d5/2 and 3d3/2 core level of the rare earth ion in these bioinorganic complexes also becomes slightly larger than that of the free rare earth atom due to the effect of the crystal field from the biological ligands.

Thermal decompositions of some bioinorganic complexes of europium

Thermogravimetric and derivative thermogravimetric investigations for three kinds of bioinorganic complexes of europium with N-acetyl-DL-alanine, N-acetyl-DL-valine and DL-alanyl-DL-alanine have been performed. It was found that the water molecules in these solid state complexes are not directly coordinated to the europium ion and that there may be three or four steps in the thermal decomposition process of these complexes after dehydration. The possible thermal decomposition reactions of these bioinorganic complexes have been suggested and discussed.

Thermal decomposition process of some rare-earth-nitrilotriacetic acid-serine mixed complexes

Thermal decomposition processes of the mixed complexes of nitrilotriacetates of Pr, Sm, Tb, Ho and Tm with 2-amino-3-hydroxypropionic acid have been investigated. The results indicate that serine may coordinate to the rare earth ion via its hydroxyl group, not by means of its carboxyl group. From the thermogravimetric and the derivative thermogravimetric curves it can be deduced that there may be six or seven steps in the thermal decomposition process of these mixed complexes, and that not all thermal decomposition processes in these mixed complexes are the same. Some possible thermal decomposition reactions have been proposed, and the differences between the thermal decomposition processes of these complexes are also discussed.

RESEARCH ON THE THERMAL-DECOMPOSITION OF THE BIOINORGANIC COMPLEX OF EUROPIUM AND L-GLUTAMINE BY MOSSBAUER-SPECTROSCOPY

Abstract Mossbauer spectroscopy has been used to investigate the thermal decomposition of the bioinorganic complex of europium and l -glutamine. The Mossbauer parameters can demonstrate that the water molecules in the complex and the chlorine anion in the hydrogen chloride molecule, dissociated from the complex below 200°C, are not linked directly to the europium atom. The thermal decomposition process of the complex is discussed and a possible coordination model for the europium l -glutamine complex is also proposed on the basis of the thermogravimetric and derivative thermogravimetric curves, and from some evidence obtained from the Mossbauer effects of some decomposition products of the complex.

THE STUDY OF MOSSBAUER-EFFECT IN EUBA2CU3O7-Y

EuBa2(Cu1-xFex)3O7-x has been investigated by the57Fe and151Eu Mössbauer effect. The57Fe Mössbauer spectra of the EuBa2(Cu1xFex)3O7-y without or with DC electric current (the current strength I=0.5A) around the superconducting transition temperature have been measured. The results indicate that the isomer shift (IS) and the quadrupole splitting (QS) of the Fe replacing the Cu(2) vary neither with increasing the Fe content nor with the small DC eletric, current passing the superconductor and that the IS and the QS of the Fe replacing the Cu(1) vary with the Fe content. Especially, the IS and the QS of the Fe (D3) replacing the Cu(1) are changed when the small electric current passes the superconductor at 80K.