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Jugend und Sport (J + S) ist das größte Schweizer Sportförderungssystem und vereint in einem staatlich subventionierten und inhaltlich regulierten Ausbildungssystem über 90 Sportarten. Um die Qualität der Sportaktivitäten zu gewährleisten, bedarf es einer ansprechenden und qualitativ hochwertigen Ausbildung von J + S-Leiter*innen. Im J + S-Ausbildungsmodell werden im Handlungsbereich „Vermitteln“ Ausbildungsinhalte zu qualitätsvollen J + S-Aktivitäten an die Leitenden weitergegeben, welche sich eng am aktuellen Forschungsstand der Unterrichtsqualitätsforschung orientieren. Zur systematischen Evaluation dieses Handlungsbereichs in der Praxis wurde das J + S-Evaluationsinstrument entwickelt. Damit sollen die an J + S-Aktivitäten teilnehmenden Kinder und Jugendlichen mittels Fragebogenitems zu vier Handlungsbereichen digital befragt werden.

The possibility of synthesizing layered oxycarbonates, with nominal composition Sr4Fe2-xMxO6CO3 (with M = Sc, Co, or Ni) involving trivalent scandium, cobalt, or nickel, with 0 ≤ x ≤ 2 (M = Sc), 0 ≤ x ≤ 1.5 (M = Co), and 0 ≤ x ≤ 1.1 (M = Ni), is reported for the first time. The structural studies of Sr4Sc2O6CO3 and Sr4FeMO6CO3 (M = Co and Ni) show that these three phases are closely related to the n = 3 member of the Ruddlesden−Popper family. They derive from the latter by replacing the middle layer of transition-metal octahedra by triangular CO3 groups, with two different “flag” and “coat hanger” configurations. Magnetic behaviors that are fundamentally different from the magnetic behavior of Sr4Fe2O6CO3 are also reported.

A very large oxygen deficiency has been detected in an n = 2 member of the Ruddlesden and Popper (RP) series, Sr3FeCoO7-x, with x reaching 1.55. For any x, the compounds are tetragonal I4/mmm with a ≈ 3.85 Å and c ≈ 20.2 Å, a and c decreasing with x. The neutron powder diffraction (NPD) study of the most oxygen deficient phase, x = 1.55, shows that the oxygen vacancies are located in the common apex and in the basal plane of the double perovskite layers, leading for cobalt and iron to local tetrahedral and pyramidal coordinations. XANES spectroscopy reveals a divalent oxidation state for cobalt with strongly distorted tetrahedral coordination, whereas iron exhibits a trivalent state with a square pyramidal environment. This observation associated with the low dimensional character of the structure lead to complex magnetic properties. When the oxygen content is increased to x = 1.1, the formal charge of cobalt first increases to Co³⁺ whereas its coordination changes from tetrahedral to square pyramidal, Fe³⁺ being unchanged. For an oxygen stoichiometry close to 7 (x = 0.1), both cations are tetravalent and sit in an octahedral environment. Physical properties are also discussed.

Abstract:: The behavior of the magnetic properties of magnetite Fe3O4 irradiated by swift heavy ions is investigated by magnetization measurements. Although there is no induced structural phase transformation, both coercive field and saturation magnetization are sensitive to ion irradiation and exhibit different behaviors depending on the ion fluence range. In the low fluence regime, the coercive field increases, which is evidence for a strong pinning of magnetic domain boundaries by the induced defects. The magnetization shows a decrease in the saturation value and tends to reorient perpendicularly to the ion track axis. At high fluence, the initial magnetic properties of the sample are nearly restored. The changes in the magnitude and the direction of magnetization are interpreted by magnetostrictive effects related to the stress induced by irradiation. A phenomenological model is applied to reproduce the fluence evolution of the saturation magnetization, assuming relaxation of the stress induced around the core of defects of the tracks by overlapping effects at high fluence. The results are compared to those obtained in the case of yttrium iron garnet Y3Fe5O12.

The possibility to synthesize layered oxycarbonates involving trivalent chromium has been shown for the first time for the compound Sr4Fe2-xCrxO6CO3, with 0 ≤ x ≤ 1. The structural study of Sr4FeCrO6CO3 using NPD, HREM, Mössbauer, and XANES, shows that this phase, which is closely related to n = three-member of the Ruddlesden−Popper family, is built up of layers of corner-sharing CrO6 octahedra and FeO5 pyramids. Between the layers the triangular CO3 groups, parallel to bc or ac planes, are connected to the CrO6 octahedra, adopting a “coat-hanger” configuration. The antiferromagnetic behavior of this phase (TN = 125 K) is fundamentally different from the magnetic behavior of Sr4Fe2O6CO3.

Activity and selectivity of molybdenum phosphates, Cd1−xFex-MoPO6(x=0→1) and AgMo3P2O14, were compared for the propane mild oxidation reaction (C3H8/O2/N2=60/20/20, W/F=3.5 g h L−1). Despite different initial molybdenum oxidation states in the CdMoPO6and AgMo3P2O14compounds, both catalysts exhibited almost the same performance. At 733 K, propane conversion reached 6.5% and mild oxidation product selectivity (propylene + acrolein) was 75%. On the other hand, Cd1−xFexMoPO6(x≠0) compounds were completely inactive. X-Ray diffraction and absorption wera performed before and after catalytic tests and even during the reaction in the case of AgMo3P2O14. It was shown that both active catalytic systems were modified under reactive flow; depending on their initial oxidation state, molybdenum species were either partially reduced or partially oxidized. This modification resulted in equilibration of the proportions of MoVand MoVIreaching the Mo5.25average oxidation state in both equilibrated catalysts. The intrinsic ability of the two frameworks to allow establishment of convenient MoV/MoVIbalances of 2/3 and 1/3 was a determinant factor toward activity. EXAFS studies allowed us to provide evidence of the corresponding structural relaxation phenomena. In contrast, in the case of the iron-containing compounds Cd1−xFexMoPO6, molybdenum remained pentavalent and catalytic activity was thus inhibited. The easier competitive oxidation of divalent iron into trivalent iron may be responsible for the inhibition of the MoV/MoVIredox couple.

An X-ray absorption spectroscopy study of the polycrystalline La1−xSrxCoO3(x=0, 0.25, 0.5) series at O K-edge was performed above and below the various magnetic transition temperatures. A crystal field analysis is proposed to explain the observed fine structure changes. Temperature-dependent O K-edge of LaCoO3shows evidence of smooth and continuous spin transition of Co3+from low to intermediate spin states. This result is confirmed by cobalt K-edge measurements. Upon strontium doping, O K-edges of the La1−xSrxCoO3(x=0, 0.25, 0.5) series suggested a mixed (LS–IS) Co3+/IS Co4+cobalt ion configuration. The fundamental mechanism governing the magnetotransport properties shown by the compounds is then discussed.

An investigation of the electronic structure and magnetic moments of Co2+and Ni2+cations in doped CMR manganites Pr0.5Ca0.5(Mn1−xBx)O3(B=Co with x=0.05 and B=Ni with x=0.04) was realized using soft X-ray Absorption Spectroscopy (sXAS) and soft X-ray Magnetic Circular Dichroism (sXMCD) at Co, Ni and Mn L2,3-edges. Compared to similar XAS experiments in Cr doped manganites, a smaller charge transfer character from Co or Ni 3d band to the oxygen 2p band is evidenced at low doping rate which suggest that Co and Ni ions would not participate directly in the double exchange phenomena contrary to Cr3+ions.

A new series of cobaltites (Bi0.4Sr0.45Co0.15)Sr2CoO5−δ(0.15≤δ≤0.55) related to the 1201-type structure, has been synthesized. The X-ray and neutron powder diffraction studies, coupled with transmission electron microscopy (TEM) observations, evidence an orthorhombic cell (Pnnn, a≈b≈2ap, c≈2c1201) for the lowest oxygenated phases, whereas a tetragonal cell (I4/mmm, a=b≈ap2, c≈2c1201) is observed for the highest ones. The main structural feature of this series deals with the ordering between Bi3+(Co3+) and Sr2+within the rocksalt layer [(Bi/Co,Sr)O]∞leading to the doubling of the c1201parameter. The structural transition, observed versus oxygen content, is correlated to a specific oxygen arrangement around cobalt species. The XANES investigations carried out for two limit oxygen contents, 4.53 and 4.85, show two distinct formal cobalt valences. These materials have a semi-conducting behavior with negative magnetoresistance properties which are sensitive to their oxygen content. In particular, for the tetragonal phase, a spin glass like behavior (Tcusp=38.5 K) has been observed.

Domain fluctuations at low temperature are evidenced in perovskite-type rare earth manganites by two local methods: X-ray absorption and Mössbauer spectroscopies. For the CMR compound La0.7Ca0.3MnO3, the thermal variations of the prepeak at the O K-edge, obtained by XAS measurements, show that the large prepeak observed at 300 K becomes a double peak below 200 K. These shape changes are very smooth and gradual around Tcand indicate the existence of FMMdomain fluctuations around the PMI–FMMtransition temperature. For Sm0.5Ca0.5MnO3doped with 1.5% 57Fe, the Mössbauer spectra evidence charge and magnetic ordering phenomena below Tco≈270 K. The magnetic transition, spread on a large temperature domain, is attributed to fluctuations in the antiferromagnetic state.

Abstract:: X-ray absorption spectroscopy (XAS) and soft-X-ray magnetic circular dichroism (SXMCD) at the Mn L2,3-, Cr L2,3- and O-K edges of Sm0.5Ca0.5Mn1-xCrxO3 () bulk polycrystalline samples have been performed at T=20 K below the ferromagnetic Curie temperature. We show the existence of a magnetic sublattice on each of the probed cations. Considering an electronically phase-separated system, results are compared with magnetization and resistivity measurements and a tentative correlation with magnetoresistance properties on such doped compounds is discussed.

Abstract: Hyperfine electric and magnetic interactions in Y1−z Ca z Ba2Cu3−x Fe x O6+y compounds have been studied for different rates of Fe and Ca substitution (x=0.09 and 0.24;z=0.24;y=0−1) by57Fe Mssbauer spectroscopy of powder samples obtained by different thermal treatments. Calculations of the Fe3+ EFG tensor have been performed for different coordination polyhedra in Cu1 and Cu2 sites. Variations of the direction, amplitude and of the sign of the principal component of the EFG are reported versus the iron displacement from the ideal Cu sites inside the pyramidal and tetrahedral coordination polyhedra. Calculated ΔE Q and η values are compared with the experimental ones. For the Cu2 site, faithfully probed in both oxygen-depleted and oxygen-saturated samples by fairly large fraction of residing iron atoms, the mutual orientations of the axes of the principal EFG component and that of easiest magnetization are deduced from interrelations between quadrupole parameters for paramagnetic quadrupolar and magnetic Zeeman Mssbauer spectra. In the desoxygenated samples, the coexistence of a long range 2D antiferromagnetic order and of a spin-glass order has been evidenced. For the oxygen-saturated samples, the two-dimensional spin-glass order is observed belowT f =10 K. The Mssbauer spectra under applied fields at 4.2 K show an easy polarization of the spins in the Cu2 sites.

To study the sputtering induced by the electronic stopping power dE/dx, single crystals of yttrium iron garnet Y3Fe5O12(or YIG) have been irradiated at room temperature with 195 MeV 86Kr, 400 MeV 181Ta and 150 MeV 238U ions beam. The number of sputtered iron and yttrium atoms collected upon aluminium foil placed in front of the target was measured using Rutherford backscattering spectrometry (RBS) with a 2 MeV 4He Beam. The experimental results show that the electronic stopping power threshold of sputtering Tsin this garnet is 16 ± 3keV. This value is four times higher than the electronic stopping power threshold damage creation Tein the same range of velocity ions. The sputtering yield increases linearly within the experimental errors with dE/dx. Moreover, the sputtering is non-stoichiometric.

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Study of the change induced by heavy ion irradiation in the magnetic properties of magnetite ceramics Fe3O4can be important for applications. In this work, we report on the effect of the high electronic excitation induced by lead ions on the magnetic properties of highly densified Fe3O4ceramics. The physical changes induced by irradiation have been investigated by magnetization measurements and Mössbauer spectroscopy, whereas the damage morphology has been observed by TEM. Variations of the saturation magnetization have shown original behaviour versus fluence: the magnetization starts to decrease at low fluence before recovering its initial value at higher fluence. TEM observations have shown the presence of extended spherical defects in the ion wakes. This damage morphology is very similar to that observed for krypton irradiation of the garnet Y3Fe5O12at low electronic stopping power, which is characterized by a very small amorphous volume. In agreement with this observation, Mössbauer spectroscopy, recorded below the Verwey transition, has shown the absence of a paramagnetic phase. Moreover, Mössbauer spectra exhibited an irradiation-induced anisotropy of the hyperfine magnetic field which revealed the presence of defect-induced anisotropy. Such a result led us to the hypothesis that magnetic domain walls could be pinned by the extended defects, at least for low fluences.

The synthesis of Tl2Ba2CaCu2O8(2212) films obtained byex situannealing of amorphous films, deposited at room temperature with a multitarget sputtering system, is described. The growth phenomenon of 2212 films has been extensively studied by annealing precursor thin films of variable thallium content under various O2partial pressures. The best single-phase 2212 films are obtained from stoichiometric amorphous precursor films. Such 2212 films, annealed under low oxygen pressure, exhibit a critical temperature for superconductivityTc(Resistivity = 0) at 110K with a critical current densityJc(77 K) > 106A/cm2. After annealing, the composition of these films, deduced from the backscattering spectra of4He+beam measurements, indicates a formula close to Tl:Ba:Ca:Cu = 2:2:1:2.

Magnetic garnet Y3Fe5O12 and magnetic ferrite BaFe12O19 have been irradiated at room temperature by Kr and Xe ions using the GANIL accelerator at Caen and by U ions using the Unilac accelerator at Darmstadt. These experiments allow to cover a wide range of electronic stopping power values (between 7 MeV/μm and 45 MeV/μm) using the ion beam at energy between 40 MeV/a.m.u. and 8 MeV/a.m.u. Transmission Mössbauer spectrometry has been used to determine the damage cross section A for the corresponding value of electronic stopping power. High resolution electron microscopy observations confirm the A determination for the highest value of dE/dx. The main feature is the appearance of a saturation in the damage efficiency ε = A/dE/dx above an electronic stoping power value TM. Using all the previous results, damage evolution and damage morphology description will be proposed and comparison with the chemical etching sensitivity of the magnetic garnet will be done.

In order to study the charge transfers in the mercury HTC superconductors, the valence states of heavy cations (Bi, Hg) and copper have been investigated by X-ray absorption spectroscopy. Two new mercury single-layer cuprates have been chosen: one exhibiting the “1201” type structure, Bi0.5Hg0.5Sr1.5La0.5CuO5−δ, and the second, Bi0.5Hg0.5Sr2Ca0.75Nd0.25Cu2O7−δ, of the “1212” type structure. By a quantitative analysis of the Cu K-edge, the copper formal charge has been evaluated between +2.2 and +2.25 in the [CuO2]∞planes in agreement with the superconducting properties of the compounds. At the Bi L3edge, the formal charge of bismuth has been found around +4 which is the result of a mixture of Bi3+and Bi5+in the [(Bi, Hg)O]∞planes. The Hg L3edges of some reference compounds, Hg2Cl2, HgO and CaHgO2, and of the superconductors show that mercury remains in the +2 formal charge in the latter compounds, the variation of the pre-peak (2p3/2→ 5d) intensity being due to the density of oxygen vacancies in the [(Bi, Hg)O]∞planes perpendicular to the dumbbell axis of the mercury environment.

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Y3Fe5O12 garnets have been irradiated by Mo and Xe ion beams at 2.3 and 3.3 GeV respectively. High-resolution electron microscopy (HREM), channelling Rutherford backscattering (RBS) and Mössbauer spectrometry have been used to determine the variation of the radius of latent damage track induced along the ion path as a function of the electronic stopping powers between 34 and 56 MeV cm2 mg-1. On comparing the results obtained by different experimental methods it is found that the disorder characterized by channelling RBS measurements extends over the same cylindrical volume as the paramagnetic state observed by Mössbauer spectrometry. A direct HREM measurement of the radii shows a larger cylindrical volume than both the other measurements, indicating the existence of a distorted shell around the disordered core.

The copper and cobalt valence states in the 112-phase YBa (Co2-xCux)O5have been determined from a XANES analysis: copper is mainly in the Cu(II) state whereas cobalt appears in a mixed valent state Co(II)/Co(III) in agreement with the oxygen stoichiometry. The magnetic behavior of cobalt and copper in the structure of these compounds has been determined by magnetic susceptibility measurements and by powder neutron diffraction. The evolution of inverse molar susceptibility versus temperature shows that these phases are antiferromagnetic with TNranging from 395 to 515 K. At low temperature (T< TN), one observes a second magnetic transition for 0.75 < x< 1.0 compositions. The temperature T2 corresponding to this transition increases when xdecreases. The nuclear and magnetic structures of three compositions, x= 0.4, 0.8, and 0.9, have been investigated by neutron diffraction at 1.4 K. At this temperature, the nuclear structure of these phases has the space group P4/mmmand lattice parameters a0= apand c0= 2ap. The magnetic cell is related to the nuclear cell by the relationships: a = a02, c = c0for x = 0.4 and a = a02, c = 2c0for x = 0.8 and 0.9. For the x= 0.4 compound, the magnetic moments lie in the abplane; on the other hand, the spins exhibit another component along c for x= 0.8 and 0.9 phases. The study of the magnetic structure of the x= 0.8 oxide versus temperature shows that their spins switch along the caxis as the temperature approaches T2. The values of the magnetic moment determined in this study for these phases agree with the t52ge1gconfiguration of the Co(III) ion.

Abstract:: The XAS study at Cr, Co, Ni and Mn K-edges was performed for the doped CMR manganites Ln0.5Ca0.5Mn1-xBxO3 with Ln=La, Nd, Sm and B= Cr, Co, Ni ($$(0 \le x \le 0.10)$$), on the samples that were studied previously for their ferromagnetic-metallic to antiferromagnetic-insulator transition. We observed that the formal charges of the doping elements are Ni2+, Co2+ and Cr3+. It is also evidenced that the average formal charge of the manganese is increased after doping, in agreement with the charge compensation keeping “O3” stoichiometry. These results suggest that the doping elements participate directly to the band structure.

Abstract: The irradiation damage created by the high energy heavy ions of GANIL in two ferrimagnetic oxides (BaFe12O19 and Y3Fe5O12) have been observed by Mssbauer spectroscopy. The Mssbauer spectra confirmed the paramagnetic state of the amorphous phase observed by electron microscopy. In the low energy range (E<0.9 GeV), a smooth transition to a frustrated magnetic order has been observed by decreasing the temperature down to 4.2K. In the high energy range (E>0.9 GeV), the contribution of electronic processes could explain the rate of amorphization of Y3Fe5O12.

Electronic stopping power threshold of damage creation in yttrium iron garnet (YIG) has been determined by extrapolation using the known model for nuclear and electronic damage creation calibrated by 2 MeV alpha and 510 MeV argon irradiations respectively. This value is equal 4.5$1.0 keV/nm and its is three times lower than the dE/dx value at which chemical etching appears indicating that electronic stopping power damage can exist at very low value of dE/dx for non radiolytic insulating materials.

Single crystals of Al2O3samples were irradiated at GANIL with 4.32 MeV/amu 208Pb ions to fluences of 4 × 1011and 8 × 1011ions cm−2and with 2.78 MeV/amu 238U ions to fluences of 1.2 × 1012and 2.1 × 1012ions cm−2at a temperature of 77 K. Before irradiation the samples were implanted with 101657Fe ions cm−2at 110 keV and annealed at 1673 K for 1 hour in order to introduce a local probe in very low concentration in the substitutional alumina sites. A conversion electron Mössbauer spectroscopy study (CEMS) was carried out so as to measure the effects of the high electronic energy losses. These results are discussed in comparison with those obtained by Rutherford backscattering spectrometry in channeling position. It should be pointed out that two specific iron sites appear after irradiation.

Single crystals of Si-doped yttrium iron garnet (YIG: Si) have been irradiated with 6 GeV 208Pb ions at 80 K and 300 K. The amorphization cross section, for a mean electronic stopping power of 35 MeV μm−1, was determined from the 300 K 57Fe Mössbauer spectra. When going from the crystalline to the amorphous phase, the 300 K dc conductivity was found to decrease versus fluence. This is interpreted by the lowering of the carrier mobility caused by disorder. Furthermore, the 300 K ac conductivity of amorphous YIG:Si exhibited above 10 kHz an ωαlaw, with α ⋍ 0.8, characteristic of hopping conduction. These results are discussed with respect to undoped YIG irradiated with GeV heavy ions. No significant effects neither of the irradiation temperature, nor of the electrical conductivity are observed on the damage cross section.

Damage induced in several oxide materials by swift heavy ions is presented. The discussion is based on results obtained on the following materials [Y3Fe5O12, AFe12O19(A = Ba, Sr), BFe2O4(B = Ni, Mg, Zn), ZrSi2O4, SiO2quartz, Al2O3, high Tcsuperconductors (YBa2Cu3O7 − δand Bi2Sr2CaCu2O8)] which have been irradiated by ions with atomic number ranging between 6 (12C) and 92 (238U) and energies between 0.05 GeV and 6 GeV. The damage cross section Ahas been deduced using several physical characterisations like Mössbauer spectrometry, saturation magnetisation measurements, channeling Rutherford backscattering, infrared absorption and electrical resistance measurements. Depending on the material and on the value of the electronic stopping power (dE/dx) the damage cross section varies between 10−17and 10−12cm2. Using medium and high resolution transmission electron microscopy and chemical etching of the latent track, an electronic stopping power evolution of the damage morphology has been observed leading to the definition of an effective radius Reof the latent track which can be linked to the damage (amorphous) cross section Aby the relation Re= √A/π. Moreover there is a direct correlation between these values and the damage morphology: for Re> 3 nm the latent tracks are long and cylindrical, conversely for Re< 3 nm the damage is inhomogeneous along the latent track. The effect of the irradiation temperature, of the crystallographic orientation, of the initial electrical resistivity and of the oxygen stoichiometry will be presented. In opposition to what has been usually believed it will be shown that alumina (Al2O3) is indeed sensitive to the electronic stopping power. Moreover the velocity of the incident ion has a direct influence on the damage production: the lower the velocity, the higher the damage.

Using a combination of microscopy, powder X-ray diffraction, and model building, we recently reported evidence for the first misfit layer oxide, Tl0.41(Sr0.9O)1.12CoO2 (Boullay et al. Chem. Mater. 1996, 8, 1482). In this work, we present a more detailed structural characterization from an additional high-resolution electron microscopy (HREM) study as well as extended X-ray absorption fine structures (EXAFS) from the Co K edge and the Tl LIII edge. We find a structural picture largely consistent with the one originally proposed, but much more quantitative. The work has been extended over a structural family, obtained by replacing Sr by Ca to obtain the title misfit phases. The evolution of composition and lattice parameters, as well as the magnetic and electrical transport properties of representative members of the misfit oxide family, are studied.

Bi_2-xPb_xSr₂Ca_1-xY₃Cu₂O_8+δ (0 ≤ x ≤ 1) of structural type Bi(2212) is a very interesting solid solution since we are able to adjust the critical temperature over a large range of x by mean of a mere formal exchange of charge between cations which do not belong to the essential [CuO₂]∞ planes. X-ray absorption spectroscopy was performed at bismuth, lead, and copper L₃-edges on the Bi_2-xPb_xSr₂Ca_1-x Y_xCu₂O_8+δ (0 ≤ x ≤ 1) solid solution in order to investigate the formal valence states of the elements and the correlation between hole density on the [CuO₂]∞ planes and superconducting properties. It is shown that lead substitution does affect the role of the [BiO]∞ planes which exchange electrons (holes) with the [CuO₂]∞ planes. The decrease of the hole density in the [CuO₂]∞ planes with increasing x has been correlated to the decrease of T_c's, whereas the rapid decrease of the diamagnetic volume for 0.3 ≤ x ≤ 0.7 has been understood on the basis of a segregation between bismuth- and lead-rich phases. Copyright 1993, 1999 Academic Press

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Tcoptimization of as-synthesized Tl 2212 thin films can be obtained through post-annealing treatments at low temperatures (180 and 220°C). In this paper, the optimization process was controlled by ac magnetic susceptibility measurements for theTc's and by polarized X-ray absorption spectroscopy measurements for the doping hole densities. The latter technique allows a direct insight into the hole density only in the (a,b) plane of the Tl 2212 structure. All the studied thin films are overdoped with respect to the optimum of 0.12 doping holes per copper defined previously.Tcincreases up to 6 K were observed after post-annealing treatments under an argon atmosphere and were correlated with significant reduction of the doping hole density. In contrast to what has been observed on sintered samples, a post-annealing treatment at 220°C resulted in an insufficient doping hole density, below the optimum, probably resulting from the small sample thickness.

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The magnetic ordering in the orthorhombic phases LnSr2Cu2Ga1-xFexO7(Ln= Y, Ho; 0.03 ≤ x≤ 0.95) has been investigated by 57Fe Mössbauer spectroscopy. Iron occupies the Ga site (Cu(1) site) for small doping rates (x≈ 0.03), but occupies the Cu(1) and Cu(2) sites for iron-rich compositions (0.5 ≤ x≤ 0.95). For x= 0.9, the magnetic ordering takes place below TN≈ 420 K in both the Cu(1) and Cu(2) sites. The down concave curve of the temperature dependence of the hyperfine field in the Cu(1) site suggests a rather weak coupling between the Cu(1) and Cu(2) sites. The principal EFG axis VZZis directed in both sites along the longest axis of the orthorhombic cell, i.e., perpendicular to the alternating sheets. The sign of VZZis positive for the Cu(2) sites (ΔEQ= 0.6 mm/sec) and negative for the Cu(1) sites (ΔEQ= -1.9 mm/sec). In the distorted tetrahedral site, the EFG tensor is non-axial, however, its asymmetry is small (η < 0.4). The magnetic hyperfine field is perpendicular to the VZZaxis for both sites; i.e., H lies in the plane of the shortest axes. A structural analysis by electron microscopy reveals the presence of a large number of defects in the (Fe, Ga)O chain ordering as well as in the basic structure. The presence and the abundance of these defects is in agreement with the Mössbauer observations.

A new silver molybdenum phosphate, AgMo3P2O14, involving a mixed molybdenum valency, was found to play a role in mild propane oxidation (6% propane conversion, 70% propene selectivity, 6% acrolein selectivity at 733 K). Comparisons with results obtained with other molybdenum phosphates showed that silver presented a positive influence when it was able to migrate inside the MoPO host lattice. Characterizations of this catalyst, by XRD, X-ray absorption spectroscopy, and XPS, performed before and after catalytic tests, emphasized the importance of the redox couple MoV/MoVI. Moreover, the ability of the framework to allow the establishment of a correct MoV/MoVIbalance of 2/1 was found to be a determining factor.