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A Cu 12 Sb 3.6 Bi 0.4 S 10 Se 3 glass was prepared by melt spinning and crystallized by heat treatments at selected temperatures, the total preparation procedure taking less than one day. The sample characterization by powder X-ray diffraction, scanning and transmission electron microscopy complemented with EDS indicate the formation of compact materials, with a tetrahedrite relative weight fraction higher than 90% when treated at temperatures close to the crystallization peaks (∼200° C). Selenium enters the tetrahedrite structure, while bismuth precipitates in submicron and nanosized spherical shape phases depleted in copper and enriched in antimony, sulfur and selenium (when compared with the matrix composition). The characterization of electrical transport properties (electrical resistivity and Seebeck coefficient) indicate a behavior similar to that obtained by other methods on Cu 12 Sb 4 S 13 , with a maximum power factor of ∼400 μW/K 2 m at room temperature.

Anthelmintic resistance was explored by fecal egg count reduction test in a sheep flock from the French Pyrenees at the request of the veterinary practitioner after a poor response to anthelmintics was noted. The FECRT confirmed the suspicion with a mean percentage of reduction in egg excretions of 45% (CI 95%: - 40 to 78.5) and 0% (CI95%: - 162 to 49) within the ivermectin and the benzimidazole groups respectively. Haemonchus contortus was shown to be the IVM and BZ resistant species after morphological and molecular characterizations whereas Teladorsagia circumcincta was probably resistant to BZ only. The H. contortus population was still susceptible to moxidectin, closantel and levamisole. As this sheep flock is a transhumant flock, the spread of this multiple-resistant Haemonchus contortus population to the other sheep flocks sharing the same pastures in Pyrenean Mountains is highly likely. From the knowledge of the authors, this is the first report of multi-resistance to ivermectin and benzimidazole of a Haemonchus contortus population in mainland France.

Materials based on Cu12Sb4S13 tetrahedrites have been seen in recent years as promising materials for thermoelectric applications. However, the effect of small amounts of additional elements (used to tune the electrical transport properties) on the formation of the phases was not investigated. In this work we present such study, by means of powder X-ray diffraction, scanning electron microscopy complemented with energy-dispersive spectroscopy, and differential scanning calorimetry, using the Taguchi method to design the experiments. The effect of Ni, Bi and Se (i) in the volume percentage of tetrahedrite, (ii) in the temperature at which the Class III (tetrahedrite + chalcostibite + antimony → skinnerite) reaction occurs and (iii) in the final melting temperature of Cu12−xNixSb4−yBiyS13−zSez materials rapidly cooled from 950 °C was investigated. Se was observed to have a strong positive influence on the formation of tetrahedrite, while Ni and Bi were seen to promote the decrease of its volume percentage. A decrease of the Class III reaction and final melting temperatures was also observed after the introduction of Se, with Ni inducing the increase of the reaction and the decrease of the melting temperatures and Bi having only minor effects. The analysis of the microstructures indicate that high Ni concentrations lead to the first solidification of the NiS phase, while in the other compositions the (tetrahedrite/skinnerite) phase or mixtures of phases is first formed.

Copper nanopowders were sintered using Spark Plasma Sintering (SPS). Special attention was paid to the presence of natural surface oxide and reductive thermal treatments under H 2 atmosphere were carried out to remove it. The sintering mechanisms were investigated by the means of disrupted experiments at various temperatures to reach different shrinkage rates. Optimized experiments were also carried out to reach a maximum densification. The samples were characterized and compared using density measurement, X-ray diffraction, mechanical tests (tension and compression) and analysis of the fracture surfaces with scanning electron microscope. On the one hand, it results that during the SPS treatment, the raw powder undergoes a series of oxide transformations from CuO to Cu 2 O. On the other hand, reductive treatment drastically decreases the sintering temperature, from 650 °C to 260 °C, to reach 90% density without grain growth. Higher mechanical strength, up to 750 MPa, also shows better consolidation.

Perovskite-type lanthanum manganite (LaMnO3) was synthesized from Mn2O3 and La2O3 precursor powders using the Spark Plasma Sintering technique (SPS). The in situ reaction proceeds in a few minutes at 1000 °C under 50 MPa with a very high heating rate of 100 °C/min. The Rietveld refinement of the X-ray powder diffraction shows that LaMnO3 sample crystallizes in a perovskite structure of O′-type orthorhombic symmetry with Pbnm space group. After annealing at 1000 °C in air for 10 hrs, the symmetry changes to rhombohedral with R-3c space group. For the as prepared sample, two critical temperature points in the temperature dependence of the ZFC and FC magnetization occurring at 125 K and 145 K are observed. They are suggested to be related to A-type antiferromagnetic Neel temperature and ferromagnetic short range order, respectively. The ferromagnetic component in the annealed sample increases indicating the expected variation in the concentration of Mn3+ and Mn4+ ions, which was attributed to the oxygen stoichiometry effects.

International audience; The sintering of the 80GeSe2-20Ga2Se3 chalcogenide glass composition as well as the preparation of the corresponding glass-ceramics has been investigated using pulsed current electrical sintering also known as spark plasma sintering. Amorphous powder has been synthesized by mechanical alloying. Due to the electrical insulating property of this glass composition, powder is heated mostly through the heating of the graphite die. It was found that densification of glass powder occurs through a viscous flow mechanism prior to devitrification. A model has been successfully applied to determine the viscosity and activation energy of the glass. This model has been confirmed by ball penetration technique to determine the glass sample viscosity.

Laser evaporation of carbon-rich uranium/carbon alloys followed by atom reactions in a solid argon matrix and trapping at 8 K gives weak infrared absorptions for CUO at 852 and 804 cm(-1). A new band at 827 cm(-1) becomes a doublet with mixed carbon 12 and 13 isotopes and exhibits the 1.0381 isotopic frequency ratio, which is appropriate for the UC diatomic molecule, and another new band at 891 cm(-1) gives a three-band mixed isotopic spectrum with the 1.0366 isotopic frequency ratio, which is characteristic of the linear CUC molecule. CASPT2 calculations with dynamical correlation find the C[triple bond]U[triple bond]C ground state as linear 3Sigma(u)+ with 1.840 A bond length and molecular orbital occupancies for an effective bond order of 2.83. Similar calculations with spin-orbit coupling show that the U[triple bond]C diatomic molecule has a quintet (Lambda = 5, Omega = 3) ground state, a similar 1.855 A bond length, and a fully developed triple bond of 2.82 effective bond order.

The Ba8ZnxGe46−x−y◻y (4 ≤ x ≤ 8, ◻ = Ge vacancy) solid solution crystallizes in the clathrate type I structure as indicated by X-ray powder diffraction and transmission electron microscopy. The fraction of vacancies (y) derived from electron probe microanalysis varies like y = 3.3 − 0.54x for 0 ≤ x ≤ 6 and y = 0 for 6 < x ≤ 8. A simplified band picture can explain how the ratio (2−)/(4−) of formal oxidation numbers of zinc and of vacancy leads to the ∼1/2 slope of the y = f(x) relation. Hall effect measurements indicate that the Ba8ZnxGe46−x−y◻y definitely deviate from the Zintl rule when 0 ≤ x < 4, weakly deviate from the the Zintl rule when 4 ≤ x ≤ 6, and fulfill the Zintl rule when 6 < x ≤ 8. Resistivity versus temperature data for 4 ≤ x ≤ 8 are in line with a “bad metal” behavior (x ∼ 4) evolving toward a degenerate semiconducting behavior (x ∼ 8). The Seebeck coefficient increases with x in agreement with the charge carrier concentration variation and reaches −67.1 μV/K in Ba7.95Zn7.83Ge38.17 which a...

We report here our results showing the occurrence of magnetic order in the intermetallic compounds NdCu2Sn2 and PrCu2Sn2. For comparison, non-magnetic analogue, LaCu2Sn2, was also prepared. X-ray diffraction (XRD) result confirms that all the three compounds form in the tetragonal CaBe2Ge2-type structure. A cusp is observed at not, vert, similar3 K in the magnetic susceptibility of NdCu2Sn2 and PrCu2Sn2, which arises due to the antiferromagnetic ordering of the magnetic moments in these two compounds. The bulk nature of magnetic order in both the compounds is confirmed from the observation of peaks in the heat capacity at the magnetic transition temperature. X-ray absorption measurements at the LIII edge show that Pr ions are in the trivalent state in PrCu2Sn2., © Elsevier

Based on an analysis of the geometric crystallographic relations a general classification scheme is presented for intermetallides with four-coordinated networks isomorphous with hydrate clathrates. We prepared novel europium substituted clathrates, Eu 2-x (Sr,Ba) 6-x M y Si 46-y (M=Al, Ga), consistent with the standardized clathrate I-Ba 8 Al 16 Ge 30 type structure (space group Pm3n). Europium atoms in Ba compounds preferentially occupy the 2a position and thus form a new quaternary version of the Ba 8 Al 16 Ge 30 structure type. All clathrates studied are metals with low electrical conductivity. The negative Seebeck coefficients indicate transport processes dominated by electrons as carriers. Eu 2 Ba 6 Al 8 Si 36 and Eu 2 Ba 6 Ga 8 Si 36 exhibit long-range magnetic order below 32 and 38K of presumably ferromagnetic type. Magnetic susceptibilities indicate an Eu 2+ ground state, in fine agreement with L III absorption edge spectra.

Single crystals of the novel ternary compounds EuZn 2 Si 2 and EuZn 2 Ge 2 were grown from pure gallium, indium, or zinc metal used as a flux solvent. Crystal properties were characterized using X-ray single-crystal analyses via Gandolfi and Weissenberg film techniques and by four-circle X-ray single-crystal diffractometry. The new compounds crystallize with ternary derivative structures of BaAl 4 , i.e., EuZn 2 Si 2 with ThCr 2 Si 2 -type ( a =0.42607(2) nm, c =1.03956(5) nm, I 4/ mmm , R 1 =0.038) and EuZn 2 Ge 2 with CaBe 2 Ge 2 -type ( a =0.43095(2) nm, c =1.07926(6) nm, P 4/ nmm , R 1 =0.067). XAS and magnetic measurements on EuZn 2 Si 2 and EuZn 2 Ge 2 revealed in both compounds the presence of Eu 2+ ions carrying large magnetic moments, which order magnetically at low temperatures. The magnetic phase transition occurs at T N =16 and 7.5 K for the silicide and the germanide, respectively. In EuZn 2 Si 2 there occurs a spin reorientation at 13 K and furthermore some canting of antiferromagnetically ordered moments below about 10 K. In EuZn 2 Ge 2 a canted antiferromagnetic structure is formed just at T N .

The application of the cathodic protection, as well as the formation of the Ca, Mg deposit that results, are currently very defined but solely in marine environment exempt of bacteria, as the open ocean. The investigation in natural sea water, in presence of sulphogenic bacteria, achieved on long terms (two months) are infrequent. The calcareous deposit evolution is mainly function of different parametres : the cathodic protective potential, the application time of this one, the yield Mg/Ca of the middle, its microbial load and the organic matter presence dissolved. In artificial sea water, the deposit now presents some features known, so magnesium appears solely for very cathodic potentials, returning the pH favorable to its precipitation. As for the calcium, it can be formed down to weaker pH. However, for kinetics reasons, magnesium can appear earlier. In sea water to weak bacterial pollution, magnesium appears little for potentials cathodic since –800 mV/ECS. However, more the application time increases (until two months) more the quantity of calcium increases and cover magnesium. In sea water where the bacterial concentration (at least 108 Bacteria reducing sulphate and thiosulphate.ml-1) is important, the features of the deposit remain the same. Only the compactness and the density of the deposit are different : they increase in presence of bacteria. This survey shows that : the bacterial presence and more especially the bacteria sulfurogenes, the chemical composition of the sea water and the concentration in dissolved oxygen, are factors influencing the formation and the evolution of the deposit calcareous more or less.

It has been claimed earlier ( J. Alloys Comp. 186, 223 (1992)) that Ce 2 Ni 22 C 2.75 is ferromagnetic at room temperature. In this paper it is shown, with magnetic susceptibility and electrical resistivity measurements, that no ferromagnetic order exists in our Ce 2 Ni 22 C 2.75 sample down to 1.7 K. Moreover, the temperature dependencies of both magnetic susceptibility and electrical resistivity agree well with the existing theoretical models for intermediate valence fluctuating compounds. This agreement together with X-ray absorption spectroscopy data obtained at two fixed temperatures, 10 and 300 K, clearly give evidence for a nonintegral valence state of Ce in Ce 2 Ni 22 C 2.75 .

As part of a program monitoring the contamination of Cetaceans by heavy metals on the French Mediterranean coast, the levels of cadmium, copper, mercury, nickel, lead and zinc in nine striped dolphins (Stenella coeruleoalba), stranded dead on the beach in 1996 and 1997, have been worked out. The results obtained were compared to those of a similar study carried out in 1990 and 1991 on the same species. A significant decrease in the concentrations of copper, mercury, nickel and lead was shown, as well as a slight decrease in the concentrations of cadmium. Contamination by zinc was not lower and remain rather high. These results are most likely the consequence of the efforts made to clean up the coast, inadequat as it may be. Indeed, the metallic contents of the most contaminated dolphins still remain high and pose a toxicological problem which is discussed, with emphasis on mercury. Cetacean are reliable biological indicators and irrefutable evidence of the chronical poisoning of the sea and of the danger ...

Background. Delayed graft function (DGF) has remained an important complication after renal transplantation. The exact causes of DGF remain to be clarified, particularly the impact of retrieval conditions and preservation factors. In the present investigation, 1HNMR spectroscopy of urine was assessed in order to detect the influence of retrieval condition on renal medulla damage. Methods. The isolated perfused pig kidney (IPK) was used to assess initial renal function from multiorgan donors (MOD) or single organ donors (SOD) after in situ cold flush and 24-h cold storage (CS) preservation with two standard preservation solutions: Euro-Collins (EC) and University of Wisconsin (UW) solutions. Kidneys flushed with cold heparinized saline and immediately perfused were used as the control group. Kidneys were perfused for 90 min at 37.5°C for functional evaluation. During reperfusion, renal perfusion flow rate (PF) was measured. Glomerular filtration rate (GFR), tubular reabsorption of Na+, and lactate dehydrogenase (LDH) and N-acetyl-β- d -glucosaminidase (NAG) excretions were determined. Ischemia–reperfusion impairment was also determined by histological techniques and 1HNMR spectroscopy. Results. PF, GFR, and tubular reabsorption of Na+ were significantly decreased in experimental groups when compared to the control group but there was no significant difference between experimental SOD groups. GFR was significantly greater in UW-MOD than in EC-MOD and tubular reabsorption of Na+ was significantly greater in UW-MOD than in EC-MOD after 45 min of reperfusion. The release of LDH in the effluent and the urinary excretion of NAG were not significantly different after 24-h CS in the various experimental groups. The most relevant resonances determined by 1HNMR spectroscopy were citrate, trimethylamine-N-oxide, lactate, acetate, and amino acids. Excretion of these markers was significantly different when compared to biochemical markers. A resonance (P) detected particularly in EC-MOD after 24-h CS was identified and well correlated to renal dysfunction. Histological study showed that ultrastructural damage and mitochondrial injury were more pronounced in the EC-MOD group. Conclusion. These results show that retrieval condition influences renal medullary damage. NMR spectroscopy, which is a noninvasive and nondestructive technique, is more efficient in assessing renal damage than conventional histology and biochemical analysis.

Compounds YbTGa2 with TNi, Pd, Pt and alloys YbPd1−xAgxGa2 have been synthesized by argon high frequency melting from metal ingots in tantalum crucibles followed by homogenization annealing at 600 or 400°C respectively. From X-ray powder diffraction data. Yb{Ni.Pd,Pt}Ga2 was found to be isotypic with MgCuAl2-type, with a small solid solubility for Ag in YbPdGa2 (0 ⩽ x ⩽ 0 2). At 600°C the solid solubility of Pd in βYbAgGa2 (βYbAgGa2-type) was 0.7 ⩽ x ⩽ 1.0. The YbTGa2 (T = Ni, Pd, Pt) compounds are paramagnets, where the ytterbium adopts the 2 F 7 2 ground state. The magnetic results of the solid solution YbPd1−xAgxGa2 are characterized by an intermediate or mixed valence behavior of the ytterbium atom (Yb2+a Yb3+), whereas XAS measurements establish a mixed valence system.

Ternary compounds CeMSb2 and CeM′Bi2 have been synthesized by arc melting followed by a heat treatment at 400, 600 or 800°C for 300 h. Bismuth-containing compounds have been observed for the first time. From X-ray powder diffractometry all compounds were found to be isotypic with ZrCuSi2-type. In CeMn0.9Sb2, the manganese sublattice orders ferromagnetically at T∼130 K, and the cerium sublattice shows additional ordering at ∼20 K. CeMSb2 (M=Fe, Ni, Pd, Cu, Ag, Au, Zn) are antiferromagnets below T=12 K. In the paramagnetic regime, the cerium atom adopts the Ce- 2 F 5 2 tripositive groundstate. CeCu0.9Bi2 is also an antiferromagnet, whereas for Ce(Ag,Zn)Bi2 no magnetic order was encountered. X-Ray absorption spectroscopy shows that Ce in all compounds CeMSb2 and CeMBi2 is in the trivalent, or nearly trivalent, state.

This paper reviews the semiconducting glasses for thermoelectric applications. Several examples of tellurium-based glasses, with high Seebeck coefficients, very low thermal conductivities and tunable electrical conductivities, are presented, pointing this family of glasses as a good candidate for high-performance thermoelectric materials.

Recently we reported superconductivity in Y-Ni-B-C system, the first known quaternary superconducting system. One of the superconducting materials reported by us had the nominal chemical composition YNi4BC0.2. We examine, in this paper, effect of replacing nickel by palladium which is an obvious and natural step for us since we believe that the d-electrons are carriers of superconductivity in these materials. Our samples with the nominal composition YPd4BC(x) (0.2 < x < 1) have a superconducting minority phase with transition onset temperature as high as 22 K. Some of the samples show another superconducting transition at approximately 10 K, indicating one more superconducting phase in this sytem. We have also investigated LuPd4BC0.2, (Lu being the end member of the rare earth series) which also shows existence of a superconducting phase with T(c) approximately 10 K.

Fukuhara et al. reported SmRuSn3 to be the first Sm-based valence-fluctuating (VF) ternary compound which also orders magnetically. We report here our results of X-ray diffraction, microprobe analysis and L(III)-edge X-ray absorption measurements. We argue that Sm ions are VF at only one crystallographic site (2a); Sm ions at the other site (6d) are in a stable trivalent state. This assignment of the valence state is consistent with our magnetic-susceptibility and specific-heat measurements.

We have observed a superconducting transition at 12 K in the system Y-Ni-B (nominal composition: YNi4B). Sharp drop in resistivity (it does not go to zero) and a diamagnetic susceptibility below 12 K clearly indicate a superconducting transition. Possibility of a magnetic phase transition at this temperature is ruled out by our specific heat measurements. Superconducting fraction of our samples, as estimated from Meissner effect measurements, is about 2%.

Various structural aspects of two well-known varieties of MnO2: the pyrolusite (and its synthetic equivalent β-MnO2) and the ramsdellite are re-examined by studying the long-range order from previous X-ray diffraction results and the short-range order using EXAFS. From both, it is concluded that, in EXAFS fitting procedure, local Mn neighbors must include two Mn shells and two oxygen shells. These studies are extended to a third variety, the γ-MnO2, whose structure is supposed to be based on intergrowth domains of the two previous varieties. The two types CMD and EMD of γ-MnO2 used in commercial batteries are investigated. EXAFS is shown to be a powerful technique to define exactly structural aspects on those poorly crystallized materials.

We report here the changes in the europium valence in Eu 1−x Ln x Pd 2 Si 2 (LnLa, Y, Yb; 0 x - III absorption edge spectroscopy. On the basis of the simple unit-cell volume considerations and from the fact that the unit-cell volume of EuPd 2 Si 2 is intermediate between that of LaPd 2 Si 2 and Y(Yb)Pd 2 Si 2 , one expects the europium valence to vary in both cases as a function of x , with the variation taking place in the opposite directions in the two pseudoternaries Eu 1−x La x Pd 2 Si 2 and Eu 1−x Y(Yb) x Pd 2 Si 2 . However, we find that the valence does not change as a consequence of lanthanum substitution and increases with the addition of yttrium (ytterbium). These results are discussed in terms of the local environment of europium atoms in these systems.

We have performed XANES measurements at the Pr L III -edge (∼5950–5980 eV) in Y 0.8 Pr 0.2 Ba 2 Cu 3 O 6.95 , PrBa 2 Cu 3 O 6.94 and in PrBa 2 Cu 3− x Co x O y ( x =0.2, 0.3, 0.4, 0.5, 1.0 and y =6.99, 7.0, 7.01, 7.05, 7.29, respectively). By comparing these spectra with those of praseodymium oxides (PrO z , z =1.5, 1.71, 1.8, 1.83, 2) we derived the valence ( v ) of Pr in these compounds. In Y 0.8 Pr 0.2 Ba 2 Cu 3 O 6.95 v =3.4 (±0.1) and in PrBa 2 Cu 3 O 6.94 v =3.18 (±0.05). Upon doping with Co, v decreases progressively to v =3.0 for x ∼0.4–0.5 and remains constant for x >0.5.

We report here preliminary investigation of the effect of hydrogen absorption on superconductivity in the borocarbide superconductors YNi 2 B 2 C. Our experiments show that hydrogen is absorbed to a low molar concentration of ∼ 0.2 and that hydrogen has no significant effect on the lattice parameter and superconducting transition temperature. These results are the first report on effect of hydrogen in quaternary borocarbides.

The series Gd(Mn1−xInx)2 was investigated with particular attention to the influence of In/Mn substitution on structure and physical properties. X-ray diffraction patterns show the formation of solid solutions crystallising with Laves-type structures in the sequence of cF24-MgCu2 (0

We report here our discovery of bulk superconductivity at rather high ${\mathit{T}}_{\mathit{c}}$ in samples having nominal compositions ${\mathrm{YNi}}_{4}$${\mathrm{BO}}_{0.2}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}12.5 K) and ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{3}$${\mathrm{O}}_{0.2}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}13.5 K). While ${\mathrm{YNi}}_{4}$${\mathrm{BC}}_{0.2}$ seems to be a single phase material, ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{3}$${\mathrm{C}}_{0.2}$ is a multiphase system. Our experimental results show that the two materials are distinct superconductors. Discovery of superconductivity in these materials is of significance since not only is their ${\mathit{T}}_{\mathit{c}}$ high (g10 K) but they also have nickel in large proportions. No nickel-based ternary superconductor was previously known.

SmRuSn3 is a unique compound among the known Sm‐based valence fluctuation (VF) systems. Its crystallographic structure has two inequivalent Sm sites and Sm ions at only one of them are in VF state while the Sm ions in the other site orders magnetically. Our 119Mossbauer studies show a quadrupolar splitting at the Sn site, consistent with the noncubic symmetry of the Sn site. A broadening of the Mossbauer spectrum is seen due to magnetic ordering of the material. The transferred hyperfine field at Sn site at 4.2 K is small.

Homogeneous single crystals of EuO, Eu rich EuO and Gd doped EuO have been obtained and characterized by X-ray, microprobe analysis ; Mossbauer, infrared spectroscopy and resistivity measurements versus temperature. Photoconductivity, Hall effect, optical and magnetic measurements are reported. They are interpreted within a simple model taking into account Coulomb, kinetic and exchange energies and considering the degree of compensation of the donor level due to oxygen vacancies or Gd atoms.

Studies of the transition from black semiconductor (B) to gold metal (M) in Sm1−xGdxS (x = 0.14, 0.18) were performed on both sides of the critical concentration (xc ≈ 0.16). Measurements of the lattice parameter versus the temperature (12–300 K) for Sm0.82Gd0.18S showed that the limits of the temperature region in which the M and B phases coexisted depended on the direction of the temperature cycles but not on the number of cycles (up to three). LIII absorption edge measurements were used to determine the valence state of samarium at temperatures in the range 20–300 K. The extended X-ray absorption fine structure (EXAFS) spectra are very different for the two compounds. The EXAFS data for the first nearest-neighbour sulphur atoms of each samarium ion can be fitted to one mean distance and an [Sm 2+ ] [Sm 3+ ] ratio which corresponds to the valence deduced from the LIII edge and two energy thresholds. This distance changes as the lattice collapses at the B → M transition. To fit the data for the sample with x = 0.14 some disorder effects must be added in the high temperature phase.

Single crystals of Gd doped EuO have been grown with an initial Gd concen­ tration of 1.5%. The lattice parameter has been determined by X-ray analysis and is smaller that of pure EuO. Measurements of resistivity under hydrostatic pressure have heen performed up to 5 Kbar in the temperature range 50 K - 200 K. The carrier concentration has been determined at high and low temperature by Hall effect measu­ rements. The Curie temperature has been determined by magnetization measurements. The main points of interest of this work are : i) the resistivity decreases under pressure while it increases in samples of Eu doped EuO ; ii) the resistivity peak is shi­ fted by pressure towards high temperature at a rate of 0.8 K/kbar while the inflexion point of the p-vs-T curve is shifted at a rate of 0.7 K/kbar. The negative pressure coefficient of resistivity measured for this sample has been explained by the mixing of 6 s and 5 d bands ; so that the variations of resistivity under pressure are due to mobility variations because the sample remains degenerated at high and low tem­ perature.

The lattice parameters of tetragonal CeRh2Si2 are anomalous compared with those of the other members of the series CeM2Si2 (M ≡ Ru, Rh, Pd and Ag). Measurements of the susceptibility of CeRh2Si2 as a function of temperature in the range 15–300 K reveal interesting features. At high temperatures the susceptibility obeys a Curie-Weiss law with an effective moment per cerium ion that is 20% higher than that of the free Ce3+ ion. There is a cusp-like peak at about 37 K and a relatively smaller peak at 5.2 K. The lattice parameters a and c show a slight decrease between 300 and 40 K and a rather small increase between 40 and 12 K. The LIII absorption edge and the extended X-ray absorption fine structure spectra are unchanged between 20 and 300 K. This clearly indicates that the valence of the cerium ion does not change and that the first-nearest-neighbour environment (eight rhodium atoms and eight silicon atoms) of the cerium ion is not affected by the transition at 37 K.

Lattice parameter measurements in the temperature range 12 to 300 K and LIII edge measurements in the range 4.2 to 300 K are performed on the compounds CeM2Si2 (M Mn, Fe, Co, Ni, Cu) to study the valence changes. Magnetic measurements (1.6 to 600 K) for fields up to 1 T confirm antiferromagnetism of CeMn2Si2 (TN ≈ 370 K) and show enhanced Pauli paramagnetism of mixed valence compounds with M Fe, Co, Ni with spin fluctuation temperatures around 150 K with Co, Ni. Transport properties measurements show that the compounds with M Co, Ni, Fe do not become superconducting down at 18 mK and that a Fermi liquid behaviour exists in the range 40 to 70 K. Des mesures de parametres de maille dans l'intervalle de temperature (12 a 300 K) et de seuils d'absorption LIII ont ete realisees sur les composes CeM2Si2 (M Mn, Fe, Co, Ni, Cu) pour en etudier les changements de valence. Les mesures magnetiques (1,6 a 600 K) et pour des champs atteignant 1 T confirment l'antiferromagnetisme de CeMn2Si2 (TN ≈ 370 K) et montrent le paramagnetisme de Pauli renfore des composes a valence intermediaire dans CeM2Si2 (M Fe, Co, Ni) avec des temperatures de fluctuations de spins d'environ 150 K dans les cas du Co et du Ni. Les mesures de transport (M Co, Ni, Fe) montrent que les composes ne devienent pas supra conducteurs a 18 mK et qu'un comportement liquide de Fermi existe dans l'intervalle 40 a 70 K.

The authors report new materials R 2 M 3 X 5 compounds mainly based on possible anomalous rare earths: Ce, Eu and actinide U. Lattice parameters, susceptibility and L III absorption edge versus temperature measurements have been performed on Ce, Eu based materials. Mossbauer experiments versus temperature are also reported on Eu 2 Ni 3 Si 5 . Magnetism is observed on Ce 2 Ir 3 Ge 5 , Eu 2 M 3 Si 5 (M=Cu, Pd) and U 2 Rh 3 Si 5 . New intermediate valence materials have been obtained in Ce 2 M 3 Si 5 (M=Rh, Ir), with a rather small deviation from the trivalent state of Ce ion. Eu 2 Ni 3 Si 5 is an intermediate valence compound. From Isomer Shift measurements and L III absorption edge measurements versus temperature the valence of Eu changes from #2.6 at 300K to #2.7 at 4.2K.

Effects of chemical substitution in CeRu2Si2, a well-studied heavy fermion system and YbPd2Si2 have been investigated through magnetic susceptibility and x-ray diffraction in the systems CeRu x Si2, CeRu2−x Os x Si2, CeRu2Si2−x Ge x and YbPd2Si2−x Ge x . Replacing silicon by germanium generates normal chemical pressure effect, namely, Ce and Yb atoms in CeRu2Si2 and YbPd2Si2 became more and less magnetic respectively. With increasing Ge concentration, CeRu2Si2−x Ge x exhibits larger susceptibility at low temperature, goes to an antiferromagnetic state and finally becomes ferromagnetic. In YbPd2Si2−x Ge x , increasing Ge concentration drives Yb atoms to more divalent state. Electronic effects are more pronounced in CeRu2−x Os x Si2 though CeRu2Si2 and CeOs2Si2 have very nearly the same lattice parameters. It is conjectured that CeRu2Si2−x Ge x may be the first Ce-based heavy fermion having a magnetic ground state.

Magnetic behaviour of the four new Ce-based intermetallics, viz., Ce 2 T 3 X 5 ( T = Rh , Ir ; X = Si , Ge ) having orthorhombic U 2 Co 3 Si 5 -type structure has been studied as a function of temperature. Though Ce-ions in Ce 2 Rh 3 Si 5 are ‘trivalent’ as inferred from the cell constants, the magnetic susceptibility measurements, however, strongly suggest a nonmagnetic ground state (of Ce-ions) in this system. μ eff /Ce-ion and θ p as determined from high temperature Curie-Weiss behaviour, are 1.80μ B and 60K for Ce 2 Ir 3 Si 5 and 1.90μ B and 75K for Ce 2 Rh 3 Ge 5 . Ce 2 Ir 3 Ge 5 undergoes an antiferromagnetic ordering with T N = 10 K .

The superconducting and magnetic properties of La0.95Gd0.05Ru3Si2 have been investigated as a function of temperature and applied magnetic field. From measurements, the coexistence of spin glass freezing and superconductivity has been inferred below 6 K.

In earlier studies1 of the Kondo lattice antiferromagnets CeT2Si2 (T = Ag, Au, Pd, Rh) we observed the interplay between Kondo and RKKY interactions as their relative strengths were modified by pressure. In those cases (Pd or Rh) in which TK > TN, pressure strongly depressed due to Kondo spin compensation of the cerium local moments. On the other hand, when was small relative to TN (Ag or Au), magnetic order was only weakly affected by pressure. These findings correlated qualitatively with Doniach’s model2 for the magnetic phase diagram of a Kondo “necklace,” provided the effect of unit cell volumes, i.e. chemical pressure, of the CeT2Si2 were considered.

Many ternary compounds with the general formula YbM2X2 (M = transition metal, X = Si and Ge) have been prepared and studied [1,2]. In these compounds, Yb can be 2+, 3+ or intermediate valence (IV) depending on the chemical composition of the alloy [3–5]. Intermediate valence in YbPd2Si2 was first reported using x-ray photoemission spectroscopy and LIII-edge absorption [3]. The magnetic susceptibility [6] and Mossbauer [7] measurements confirmed that Yb is IV but close to 3+ valence state. Recent results on the other IV system, CeRu2Si2, showed that the Ge substitution on the Si site creates chemical pressure effects and pushes the valence of Ce closer to 3+ [8]. The Ge substitution should lead to a decrease in the valence of Yb in YbPd2Si2. However, with small concentrations of Ge introduced in the matrix, one may except an increase in the spin fluctuation temperature, (TSF). In such a case, one should see the scaling behaviour of X4f: i.e., the Yb derived 4f susceptibility X4f(T) should scale with T/TSF as X4f∼f(T/TSF) where f is a universal function.

CeRh2Si2 undergoes an antiferromagnetic phase transition at 37K which is unusually high for in Ce-based system. It is known that at moderate pressures, magnetic ordering in CeRh2Si2 is completely suppressed. Substituting Ge for Si, which is equivalent to applying a negative pressure to the system, gives rise to a very interesting effect: TN of the pseudo-ternary system CeRh2Si2-x Gex first increases (TN=38.5K for x = 0.125) and then decreases as x increases. The slope dTN(x)dx is largest at x = 1. X-ray measurements confirm that the system crystallizes in ThCr2Si2-structure for the entire range of x (0 x 2) and there is no anomaly in lattice constants. Magnetic susceptibility measurements carried out in the temperature interval 4.2K T 300K show that cerium atoms are in trivalent valence state. We argue that these observations can be understood on the basis of Doniach's Kondo-necklace model.