Z. Homonnay

Metastability in EuBa2(Cu1-xSnx)3O7-y studied by 119Sn and 151Eu Mössbauer spectroscopy.

The metallic oxide compound system EuBa/sub 2/(Cu/sub 1-//sub x/Sn/sub x/)/sub 3/O/sub 7-y/ (x = 0.05, 0.10, 0.20) was prepared for investigation with /sup 151/Eu and /sup 119/Sn Moessbauer spectroscopy. The best fits of the /sup 119/Sn Moessbauer lines reveal at least two different Sn/sup IV/ sites. The /sup 151/Eu spectra are characteristic for Eu/sup III/ state in these compounds. We have found a considerable difference between the shapes of /sup 119/Sn Moessbauer spectra recorded at room temperature and those recorded at the temperature of liquid nitrogen in the case of the sample having the highest tin content. Nevertheless, there is no evidence that this difference has a direct connection with the superconducting behavior.

Local environments of iron and cobalt in doped MgB2 superconductors

MgB2 has been doped with 57Fe and 57Co in order to probe the electronic structure of the superconductor by Mossbauer spectroscopy. Simultaneous SEM–EDX studies showed that both Fe and Co were incorporated to some extent into the MgB2 host lattice. Mossbauer spectroscopy indicated that Fe2B and FeB were also formed during the preparation. At higher Fe contents Fe2B appeared unambiguously as a secondary phase in the x-ray diffraction. CoB was detected at substitution levels of 10 mol% and greater. Both Fe and Co doping decreased the Tc(0) modestly. Co and Fe were found to substitute at the Mg site in the MgB2 lattice. The Mossbauer parameters for 57Co and 57Fe were consistent with a metallic environment. The similarity of the isomer shifts in MgB2 and in cuprate superconductors is being discussed.

Mössbauer spectroscopic investigation of the sorption of iron by polyether-type polyurethane-foam sorbents

The results of a study on the nature of the iron species sorbed by polyether-type open-cell polyurethane (PU) foam membranes are presented. The study has included freshly prepared anionic 57FeIII–halo complexes and 57Fe(SCN)3, in addition to the cationic 57FeII–phenanthroline complex. Conclusions concerning the most probable nature of the sorbed species have been drawn from the comparison of Mossbauer spectra for frozen Fe—PU foam complexes with the spectra for corresponding iron-containing frozen aqueous solutions and extracts in suitable organic solvents. For FeIII compounds, diethyl ether, and for the FeII complex, acetone, pentyl alcohol and nitrobenzene were used as organic solvents. The spectra were recorded at 80 K and evaluated to obtain isomer shifts, quadrupole splittings and internal magnetic fields for different iron species.

Metastability in EuBa/sub 2/(Cu/sub 1-//sub x/Sn/sub x/)/sub 3/O/sub 7-y/ studied by /sup 119/Sn and /sup 151/Eu Moessbauer spectroscopy

The metallic oxide compound system EuBa/sub 2/(Cu/sub 1-//sub x/Sn/sub x/)/sub 3/O/sub 7-y/ (x = 0.05, 0.10, 0.20) was prepared for investigation with /sup 151/Eu and /sup 119/Sn Moessbauer spectroscopy. The best fits of the /sup 119/Sn Moessbauer lines reveal at least two different Sn/sup IV/ sites. The /sup 151/Eu spectra are characteristic for Eu/sup III/ state in these compounds. We have found a considerable difference between the shapes of /sup 119/Sn Moessbauer spectra recorded at room temperature and those recorded at the temperature of liquid nitrogen in the case of the sample having the highest tin content. Nevertheless, there is no evidence that this difference has a direct connection with the superconducting behavior.

The Influence of Mechanical Treatment on the Absorption of CO2 by Perovskite Oxides

Perovskite oxides of composition (Sr1-xCax)(Fe0.5Co0.5)O3-δ were investigated for CO2 absorption properties and were proved to be useful as materials for CO2 absorption in the temperature range from 550 to 850 °C. The absorption rate of CO2 increased with Ca doping. The mechanical treatment of perovskite oxides for several minutes, especially for the oxides containing a small amount of Ca, was found to be effective for activating the oxides for CO2 absorption and for reducing the starting temperature of CO2 absorption by about 80 °C. However, it was not less effective to treat the oxides for a long time. The site distortion due to Sr and Ca ions at site A and the mixed valence states at site B were confirmed to be effective for CO2 absorption at high temperatures. During the absorption of CO2, a spinel compound was formed according to the following reaction: 2(Sr,Ca)(Fe,Co)O2.5 + CO2 → (Sr,Ca)CO3 + (Sr,Ca)(Fe,Co)2O4.

57Fe, 119Sn and 151Eu Mössbauer studies of (Tl,Pb)(Ba0.2Sr0.8)2Ca2Cu3Oy superconductors

Abstract The introduction of the Mossbauer nuclei 57 Fe , 119 Sn and 151 Eu into Tl-based 12( n −1) n superconductors was investigated. The doped Tl-based superconductors were characterized with respect to critical temperatures, critical currents, microstructure and composition of the superconducting and secondary phases. The samples were then analyzed by Mossbauer spectroscopy. Energy dispersive X-ray (EDX) analysis showed that both 57 Fe and 151 Eu were incorporated in the superconducting crystallites. Sn was found in secondary phases. Incorporation of Eu into the superconducting phase favored the formation of the Tl-1212 phase. The isomer shift and the electric field gradient derived from the 151 Eu spectra were consistent with Eu 3+ at the Ca site. The 57 Fe Mossbauer spectra refer to two different micro-environments for the Fe 3+ . They were assigned to Fe 3+ substituting Cu between the two Ca layers and between the Ca and Ba–Sr–O layers.

The effect of Pr substituted in Eu1−xPrxBa2Cu3O7−δ and EuBa2−xPrxCu3O7−δ perovskites

Abstract Eu1−xPrxBa2Cu3O7−δ (x=0.0, 0.1, 0.5, 0.7, 1.0) and EuBa2−xPrxCu3O7−δ (x=0.0, 0.1, 0.3, 0.5, 0.7) perovskites have been synthesized and investigated by means of 151 Eu Mossbauer spectroscopy, X-ray diffractometry, resistivity and susceptibility measurements. We have found that Pr can be introduced into the Ba site in EuBa2Cu3O7−δ high temperature superconductor. Our results show that EuBa2−xPrxCu3O7−δ is a superconductor for x≤0.7.

Microstructural study of the CO2 absorption in SrxCa1−xFe0.5Co0.5O3−δ

Abstract The absorption of CO 2 in Sr x Ca 1− x Fe 0.5 Co 0.5 O 3− δ perovskite ( x =0.95, 0.5) has been studied with the aid of 57 Fe Mossbauer Spectroscopy. Due to their remarkable CO 2 absorption capability at high temperature, Sr x Ca 1− x Fe 0.5 Co 0.5 O 3− δ -type compounds may find application in reducing the industrial CO 2 output that is a major source of the global green house effect. The Mossbauer spectra of Sr 0.5 Ca 0.5 Fe 0.5 Co 0.5 O 3− δ and Sr 0.95 Ca 0.05 Fe 0.5 Co 0.5 O 3− δ were markedly different before as well as after CO 2 absorption, indicating different microenvironments and electronic structure of the Fe atoms in the lattice. The Ca-rich compound absorbed CO 2 much faster and had twice as much total CO 2 absorption capacity than the other one. The high absorption rate was attributed to the orthorhombic layered brownmillerite structure of Sr 0.5 Ca 0.5 Fe 0.5 Co 0.5 O 3− δ , while it was concluded that the cubic structure of Sr 0.95 Ca 0.05 Fe 0.5 Co 0.5 O 3− δ , stabilized by higher O-stoichiometry, is unpreferred for CO 2 absorption. In agreement with X-ray diffraction (XRD) data, the reaction 2(Sr,Ca)(Fe,Co)O 2.5 +CO 2 →(Sr,Ca)CO 3 +(Sr,Ca)(Fe,Co) 2 O 4 is proposed to account for the absorption process.

Mössbauer study of EuBa2Cu3O6+x material

Mössbauer spectra of a mixed EuBa2Cu3O6+x oxide where x>0.5 were recorded in temperature range of 76–300 K. Between 85–300 K temperature the parameters of the appearing line in the Mössbauer spectrum are consistent with an Eu(III) state. At 76 K, however, the spectrum of the freshly prepared material exhibits two separated lines.

57Fe,119Sn and151Eu Mössbauer study of EuBa2(Cu1−x−y119Snx57Fey)3O7−δ superconductor

Abstract151Eu,119Sn and57Fe Mössbauer spectroscopy was used to study a EuBa2(Cu1−x−ySnx Fev)3O7−δ superconductor in which sites were replaced by all three Mössbauer isotopes in the same sample in order to get information about the site preferences and structural changes. We have found changes in the Mössbauer parameters of the57Fe,119Sn and151Eu spectra compared to those recorded in the separately substituted EuBa2Cu3O7−δ, EuBa2(Cu1−xSnx)3O7−δ, YBaCu3−xFexO7−δ YBaCu3−xSnxO7−δ materials. These results can be interpreted as a consequence of the site preferences and the changes in the structure due to the presence of other additional substitutional elements.