Search

Magnetic nanoparticles (MNPs) are few of the nanoparticles used clinically. When MNPs are delivered into human body, they are ingested by macrophages. We evaluated the cellular response of macrophage after MNPs loading. In face of stimulation by lipopolysaccharide, a strong stimulant derived from bacterial cell wall, MNPs loaded macrophage exhibited decreased phagocytic activity and decreased generation of cytokines such as TNF-alpha, IL-1beta whereas increased nitric oxide generation was noticed. Although these changes might decrease bactiericidal activity, it also alleviates the risk of senses, a life threatening phenomenon in infection patients. The finding has significant implications on nanoparticle based targeted drug delivery.

Transport and magnetization of MgIn 2− x Mn x O 4 polycrystalline pellets (0 x 2 O 4 with Mn results in an increase in electrical resistivity and a decrease in electron concentration. The electrical resistivity increases with decreasing temperature throughout the temperature range and variable-range hopping is observed at low temperatures. The diamagnetic pure MgIn 2 O 4 changes to paramagnetic after doping. The paramagnetism of the doped samples obeys the Curie–Weiss law. The magnetic-field dependence of the magnetization of the doped samples can be well described by the Brillouin function.

The purpose of this work was to evaluate the efficacy of labeling human mesenchymal stem cells (hMSCs) by ionic superparamagnetic iron oxide (SPIO) without a transfection agent and verifying its capability to be detected with clinical 1.5 T magnetic resonance (MR) at the single-cell level. Human hMSCs were incubated for 24 h with an ionic SPIO, Ferucarbotran. The labeling efficiency of hMSCs was determined by iron content measurement spectrophotometrically, and the influence of labeling on cell behavior was ascertained by examination of cell viability using the trypan blue exclusion method, cell proliferation analysis using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, mitochondrial membrane potential (MMP) change, differentiation capacity, and reactive oxygen species (ROS) production measured by dichlorofluorescein diacetate (DCFDA) fluorescent probe. Labeled hMSCs were scanned under 1.5 T MRI with three-dimensional (3D) and two-dimensional (2D) T2-weighted gradient echo (GRE) pulse sequences. Human hMSC labeling without transfection agent was efficient. The iron content in hMSCs was 23.4 pg Fe/cell. No significant change was found in viability, proliferation, MMP change, ROS production, or differentiation capacity. About 45.2% of the hMSCs could be detected using 1.5 T MRI at the single cell level with 3D GRE and four repetitions. Magn Reson Med 58:717–724, 2007. © 2007 Wiley-Liss, Inc.

Relative stabilities and bulk moduli of monatomic structures with coordination numbers 4 (cubic diamond or cd), 6 (simple cubic or sc), 8 (body-centered cubic or bcc), and 12 (face-centered cubic or fcc) for elements B, C, N, and O were calculated based on the first-principles. The structure for each element may be stabilized by the geometrical matching between the coordinated positions and the orbital shape. Thus, all elements favor loosely packed cd structure at low pressures, and they prefer moderately packed sc structure at high pressures. However, denser phases with bcc and fcc structures may become more stable at much higher pressures. B has only three valence electrons that are insufficient to fill up all sp 3 orbitals in a cd structure. Moreover, these three p-electrons can only fill half of the three mutually perpendicular bonds in sc structure. As a result of reduced stabilities of cd and sc structures, relative stabilities of the four structures for B are less distinctive. C has four valence electrons that match perfectly with four tetrahedral coordinated atoms. Hence, its cd structure is greatly stabilized by the extensive overlap of bonded electrons. As a result of this expanded region of stability, the equilibrium pressure between cd and sc structures is pushed up substantially. Both N and O have sufficient p-electrons to align with octahedrally coordinated atoms. Hence, their sc structures are greatly stabilized and the equilibrium pressures between cd and sc structures for N and O are much reduced relative to that for B and C. The electron density maps of cd coordination for N and O suggest that these monatomic structures may be isotropic superconductors. Bulk modulus of a symmetric structure may be determined by the average concentration of electrons in overlapped orbitals. C has the smallest atomic volume of the four elements studied, so it is uniquely capable to form the cd structure with the highest bulk modulus (447 GPa) of all structures. Although C’s p-orbitals are not fully occupied for effective bonding in octahedral coordination, its small atoms still make the bulk modulus of the sc structure the second highest (337 GPa) among various phases of the four elements studied. Except for diamond, the structures discussed above are all hypothetical. However, they may be synthesized by the bombardment of collimated beams of atoms focussed to a common center. Moreover, the structures so formed, even though they may be metastable, can be studied by the laser spectroscope fired in femtosecond (10 −15 s) bursts. Such femtochemistry has been developed by Dr. Ahmed Zewail, the latest Nobel laureate.

The nanocrystalline Nb 3 Al is prepared by the gas condensation method. The nanocrystalline Nb 3 Al size with injected 0.1mbar helium pressure is about 15nm. During the gas condensation process, the superconductivity disappears at as-prepared NC Nb 3 Al with the mean particle size about 15 nm. After annealing the as-prepared NC Nb 3 Al at 500°C for 30 minutes, the mean particle size of NC Nb 3 Al is about 30 nm and the superconductivity appear with T c about 16K. The results show that superconductivity can be achieved in nanocrystals with a rather smaller size than the typical penetration length of magnetic field. Further study of the influence of gas condensation alloying at high magnetic fields is crucial to the understanding of the superconductivity properties of NC Nb 3 Al.

High-quality ferrimagnetic superlattices Fe 3 O 4 /Mn 3 O 4 were grown on MgO(0 0 1) substrates by molecular beam epitaxy. The modulation coherency and interface sharpness are characterized by reflection high-energy electron diffraction and X-ray diffraction. Magnetization as a function of the applied field (50 kOe) and temperature (20–300 K) was measured. The magnetic response shows strong dependence on the modulation wavelength. A combined single magnetic transition temperature is predicted to be ∼600 K for samples with modulation wavelength 3 O 4 .

Nanosized particles of iron oxide (NPIO) has been applied extensively as contrast medium for magnetic resonance imaging (MRI). Recently, micrometer sized particles of iron oxide (MPIO) has also been demonstrated the feasibility for cell labeling to monitor immune response. In this study, we compared the cellular labeling efficiencies of these two kinds of magnetic particles. The NPIO exhibit stronger saturation magnetization and produce more MRI signal change. On the contrary, MPIO revealed better particle uptake ability than NPIO in incubated cells. Microscopically, both MPIO and NPIO were located in the cytoplasm but not in the cell nucleus. On MRI examination, MPIO labeled cells showed more pronounced signal change compared to NPIO labeled cells. We conclude that MPIO is more efficacious in cell labeling than NPIO. Further development and improvement of MPIO for its magnetization will facilitate its MRI applications on stem cell trafficking, evaluation of transplantation rejection and monitoring immune responses.

Magnetic resonance (MR) imaging is capable of demonstrating human anatomy and pathological conditions. Iron oxide magnetic nanoparticles (MNPs) have been used in MR imaging as liver-specific contrast medium, cellular and molecular imaging probes. Because few studies focused on the MNPs other than iron oxides, we developed FeNi alloy MNPs coated with polyethylenimine (PEI). In this study, we demonstrated PEI-coated FeNi MNPs are able to label the cells, which could be detected in MR imaging. For labelling purpose, MNPs were incubated with mouse macrophage cell line (Raw 264.7) for 24 h and these PEI-labelled FeNi alloy MNPs can be uptaken by macrophages efficiently compared with Ferucarbotran, a commercialized superparamagnetic iron oxide (SPIO) under flow cytometry measurement. Besides, these cells labelled with MNPs could be imaged in MR with the identical potency as Ferucarbotran. Further investigation of the cells using Prussian blue staining revealed that FeNi alloy MNPs inside the cells is not oxidized. This phenomenon alleviated the consideration of potential risk of nickel toxicity. We conclude that PEI-coated FeNi MNPs could be candidate for MR contrast medium.

AC susceptibility of the Rb3C60 superconductor shows a weak dependence on ac magnetic-field frequency f. The temperature, Tp where χ″ is maximum, rises with increasing frequency and the effect is enhanced as the dc magnetic-field amplitude Hdc is increased. The temperature is found to obey a scaling law (1 − T p /T c ) 3 2 = 1.9 × 10 −4 H dc [ ln (f 0 /f) + 23] + 8 × 10 −5 [ ln (f 0 /f) + 23] , where f0 (≈ 1010 s−1) is a characteristic frequency and Hdc is in tesla. The scaling relationship is in good agreement with the predicted equation based on the model of thermally activated flux motion.

Nano-cluster Ni particles with average particle size from 12–100 nm were successfully prepared by the evaporation technique. For samples with an average particle size below roughly 50 nm, we observed a nonsymmetric magnetic hysteresis loop and a deviation between the zero field cooling (ZFC) and the field cooling (FC) magnetizations at temperatures below a critical temperature Tx. Tx is a function of the applied magnetic field and the size of the nickel particles which is in general inversely proportional to the saturation magnetization of the nickel particles. This can be explained by the effect of exchange anisotropy interaction between the interfaces of the ferromagnetic region of Ni nano-clusters and the layers of antiferromagnetic NiO on the surface of the nano-cluster Ni particles. A slope variation in magnetization below a special temperature TS (roughly 50 K) for nano-cluster Ni particles with average particle sizes roughly below 50 nm has been observed. This is explained by a spin flip behaviour near the interfaces between the nano-cluster Ni particles and the layers of NiO on the surface of the Ni particles.

The (Hg0.7Bi0.3)Sr2(Ca1−xPrx)Cu2O6+δ system for 1.0 ≧ x ≧ 0.25 has been prepared. The transition temperature Tc always decreases as the rare-earth substitution parameter x increases. We observed the maximal Tc around x = 0.25 with 91 K. From the viewpoint of doping the ionic size and analytic results of the Pr valence in the x = 1.0 sample, we think that Pr exhibits the trivalent state in this system. No anomalous rare-earth Pr antiferromagnetic (AFM) ordering was observed in the temperature dependence of the susceptibility down to 5 K for the Ca free sample.

We studied the structure and magnetic properties of molecular-beam epitaxy grown 300 A thick Fe/Pt multilayers with different bilayer thickness and annealing temperature. The Fe/Pt multilayers were deposited on 100 A thick Pt buffer layers at 100 °C on Al2O3 (0001) substrates. The structure of as-deposited Fe/Pt films was fcc(111). While the postannealing temperature ⩾400 °C, an additional FePt(100) orientation was observed. A large coercivity range, namely, 200–16 000 Oe can be tuned by varying the bilayer thickness and annealing temperature.

We report on the synthesis of iron phosphide nanowires by thermal decomposition of (η4-cyclohexadiene)iron tricarbonyl in the presence of TOP (tri-n-octylphosphine) and characterization of the products.

Temperature-dependent magnetization and magnetic-hysteresis curves for the zero-field cooled and the field-cooled processes of Rb 3 C 60 superconducting fullerene with T c of 30.5±0.1 K were measured between 5 and 30 K in magnetic fields up to 1 T. Small field-cooled diamagnetism and flux jumps were observed at low temperatures and in low fields. Both results strongly suggest the existence of a rather large pinning strength in our sample. This suggestion is further confirmed by the field-cooled hysteresis curve and high critical current densities, J c ( H , T ), at low temperatures. Based on the major hysteresis loops and the Bean critical-state model, the J c at T = 5 K are 2.1 × 10 6 A/cm 2 for H = 0 T and 5.2 × 10 5 A/cm 2 for H = 0.9 T. These J c values are larger than other powdered superconductors with comparable sample sizes, except for YBa 2 Cu 3 O y . For T >10 K, J c versus H agrees well with the expression: J c ( H , T )= k 1 /(1+ H / H 01 ) n . On the other hand, for T J c ( H , T ) may be expressed as J c ( H , T )= k 2 exp(− H / H 02 ). Here k 1 , k 2 , H 01 , H 02 and n are temperature-dependent parameters. The dependence of J c on temperature thus obeys the empirical scaling relation, J c ( H , T )= J c0 ( H )(1− T / T c ) m , where J c0 and m are field-dependent parameters. For 0.4 T H m equals about 2.

We report the magnetic J c ( T ) in K 3 C 60 and Rb 3 C 60 powder samples for temperatures from 5 K to T c . J c near T c was obtained from AC measurements whereas J c at low temperatures was obtained from DC measurements. In the AC measurements, two χ″ peaks were observed on some of the samples. This is attributed to weak links in granular superconductors. The intragranular J c is much larger than the intergranular J c . The J c ( T ) data are fitted by J c ( T ) = J c (0)(1 − T / T c ) γ , with J c (0) and γ as fitting parameters. In the DC measurements on Rb 3 C 60 , J c depends approximately linearly on temperature. Extrapolating the zero-field DC data to 0 K yields J c (0) = 3.1 × 10 6 A/cm 2 . This is a rather large J c for a powdered superconductor, suggesting strong pinning in these materials. Finally, the values of γ for the intergranular and intragranular components are compared with the predictions of theories.

Ultra-fine Ni particles with average particle sizes from 12 to 100 nm were prepared by the evaporation technique. The calorimetric effects of nanocrystalline Ni as well as the NiO and Ni bulk samples were measured between 300 and 800 K. Both an exothermal effect between 380 and 480 K and an endothermal peak near 560 K were observed for ultrafine Ni; only endothermal peak was observed for both NiO near 520 K and bulk Ni near 630 K. A shifted magnetic hysteresis loop and a slope change in saturation magnetization were observed below roughly 50 K for ultra-fine Ni particles with average particle sizes roughly below 50 nm. This is explained by the effect of exchange anisotropy interaction between the interfaces of the ferromagnetic region and the layers of antiferromagnetic NO on the surface of the nanocrystalline Ni particles.

The magnetic properties and scaling behaviors in both series La 1− x Pb x MnO 3 and La 0.7 (Ba 1− x Pb x ) 0.3 CoO 3 with x =0.0–0.5 were studied. All samples crystallize in a rhombohedral R 3 C space group with a ∼0.54 nm and c ∼1.33 nm. The Pb 2+ substitution for La 3+ in the (La 1− x Pb x )MnO 3 system induces a mixed-valence state of Mn ions. The ferromagnetic transition temperature T C increases with increasing Pb content from 225 K for x =0 to 355 K for x =0.5 in the (La 1− x Pb x )MnO 3 series. For La 0.7 (Ba 1− x Pb x ) 0.3 CoO 3 samples the magnetic transition temperature is not significantly affected by the replacement of Pb ions for Ba 2+ ion and keep at about 200 K due to the constant ratio of Co 4+ /Co 3+ . All the samples exhibit the canonical spin-glass behaviors as well as the scaling behaviors.

Compositions with the rhombohedral structure have been successfully synthesized in the La 0.7 Pb 0.3 Mn 1-x Co x O 3 system. DC magnetization and AC susceptibility measurements were carried out for the entire series. The Curie temperature T c decreases with increasing x from 306 K (x = 0.0) down to 60 K (x = 0.9). The antiferromagnetic state was found near the Co-rich side (x = 1.0). Co doping tends to destroy the double exchange in Mn 4+ -O-Mn 3+ and broadens the coexistence region of the cluster-glass and ferromagnetic states.

We report the transition-metal (Mn and Co) K-edge X-ray absorption spectroscopy (XAS) study of a series of La0.7Ba0.3Mn1−xCoxO3 ( 0⩽x⩽1 ) samples. Systematic chemical shifts to higher energy with the Co content ( x ) are observed in both Mn and Co K-edge spectra. The chemical shift to higher energy in Mn K-edge spectra is caused by the decreased Mn3+/Mn4+ ratio due to Co substitution of Mn. The Co K-edge spectra show that the Co valence is between 2+ and 3+, which also increases with x . The effect of electronic structures on the physical properties are briefly discussed.

The effects of chemical size and valence on the crystal structure, magnetoresistance and magnetic properties were investigated in a perovskite-like (La 0.7 Ba 0.3 )(Mn 1 -xCox)O3 system with x = 0 - 1.0. The samples with x ≤ 0.3 and x ≥ 0.9 are of a cubic phase, but an orthorhombic phase is observed in the samples with 0.4 ≤ x ≤ 0.8. The lattice parameter, a, based on the cubic phase, at first decreases with increasing x up to 0.7, then slightly varies as x ≥ 0.8. The metal-insulator transition shows up in the compositions for x ≤ 0.2, and subsequently disappears as x ≥ 0.3. All samples exhibit ferromagnetism at low temperatures, but the long-range magnetic ordering in pure manganate (x = 0) becomes a cluster glass-type (short-range) ferromagnetic order due to the introduction of Co. The saturation magnetization decreases with increasing Co content for x ≤ 0.7, then increases as x ≥ 0.7. Our recent study using an X-ray absorption spectroscope has revealed that Co 2+ /Co 3+ and Mn 3+ /Mn 4+ , but no Co 4+ or Mn 2+ ions were observed in this entire series. The magnetotransport and magnetic properties are closely related to the average valences of Mn and Co ions.

In this investigation, we synthesize FeNi alloy magnetic nanoparticles (MNPs) by using both chemical precipitation and combustion methods. The FeNi MNPs prepared by combustion method have a rather high saturation magnetization Ms of ∼180 emu/g and a coercivity field Hc of near zero. The functionalized FeNi MNPs which were coated with biocompatible polyethyleneimine (PEI) polymer have also been synthesized. We demonstrated that the PEI coated FeNi MNPs can enter the mammalian cells in vitro and can be used as a magnetic resonance imagine (MRI) contrast agent. The results demonstrated that FeNi MNPs potentially could be applied in the biomedical field. To prepare a higher quality and well controlled Fe-Ni MNPs, we also developed a thermal reflux chemical precipitation method to synthesize FeNi3 alloy MNPs. The precursor chemicals of Fe(acac)3 and Ni(acac)2 in a molecular ratio of 1:3 reacted in octyl ether solvent at the boiling point of solvent (∼300°C) by the thermal reflux process. The 1,2-hexadecandiol and tri-n-octylphosphine oxide (TOPO) were used as reducer and surfactant, respectively. The chemically precipitated FeNi3 MNPs are well dispensed and have well-controlled particle sizes around 10–20 nm with a very narrow size distribution (± 1.2 nm). The highly monodispersive FeNi3 NPs present good uniformity in particle shape and crystallinity on particle surfaces. The MNPs exhibit well soft magnetism with saturation magnetization of ∼61 emu/g and Hc ∼ 0. The functionalized magnetic beads with biocompatible polymer coated on MNPs are also generated completed for biomedical applications.Copyright © 2006 by ASME

During the past few decades, the density of magnetic storage has been improved considerably. To increase the storage capacity, it is necessary to reduce the size of magnetic grains. However, as the domain size decreases, their thermal stability will also decrease, which results in the loss of magnetization. To overcome the limit imposed by such superparamagnetic behavior, lots of recent research attentions have been focused on the patterned magnetic media. To maximize the storage density, it is preferable to create periodical magnetic patterns, in which single-domain magnetic dots are well separated from each other. In this experiment, we have utilized nanosphere lithography to create large-area well-ordered two dimension arrays of permalloy (Ni80Fe20) nanoparticles. Nanosphere lithography is an inexpensive, simple, parallel, and high throughput fabrication technique. We have employed monodisperse polystyrene beads with diameter of 650, 560, 440, 350, 280 nm to fabricate triangle-shaped permalloy (Ni80Fe20) nano-arrays with lateral dimension in the region of 170∼90 nm, and thickness in the region of 10∼50 nm. The magnetic behavior of these triangle-shaped nanomagnet arrays have been investigated by longitudinal magnetic optic Kerr effect (LMOKE) and magnetic force microscopy (MFM). It was found that the coercivity of the permalloy nanoparticle arrays increases with decreasing the thickness of the nanoparticle. This can be attributed to the interface effect between the arrays and the substrate.

We investigated the crystallographic, transport and magnetic properties of a strongly electron correlated La0.7(Ba1−xPbx)0.3MnO3+δ series with x=0–1.0. All our samples are in a rhombohedral R 3 c structure of lattice parameters a∼0.550 nm and c∼1.338 nm . We found that the addition of the larger Pb ion in La0.7(Ba1−xPbx)0.3MnO3+δ system does not apparently affect on the metal-insulating and magnetic ordering temperatures as well as the magnetoresistance (MR) ratio. However, it reduces the sintered temperature and improves the electric conductivity. The MR ratios are monotonically linear decreasing with temperature from ∼25% at 5 K down to ∼6% at 300 K for all samples. The chemical disorder effect of the Pb2+ substitution does not change the magnetic properties at low temperatures. It can be contributed to exhibiting the constant hole concentration due to the same ratios of [Ba2+]+[Pb2+]/[La3+] and [Mn4+]/[Mn3+] in these Pb doping manganese oxides. The cluster glass behavior was apparently observed, even for the parent sample of x=0.

Paramagnetic and superparamagnetic substances are used to trace stem cell in living organisms under magnetic resonance imaging (MRI). We compared paramagnetic and superparamagnetic substance for their labeling efficiency by using clinically widely used gadolinium chelates and iron oxide nanoparticles. Without the aid of transfection agent, human mesenchymal stem cells were labeled with each agent separately in different concentration and the optimized concentration was determined by maintaining same cell viability as unlabeled cells. Iron oxide nanoparticle labeling has a detecting threshold of 12 500 cells in vitro, while gadolinium chelates labeling could be detected for at least 50 000 cells. In life animal study, we found there is an eightfold sensitivity in cells labeled with iron oxide superparamagnetic nanoparticles; however, the magnetic susceptibility artifact would obscure the detail of adjacent anatomical structures. We conclude that labeling stem cells with superparamagnetic substance is more ...

The problems of making phase-pure (Hg0.7Bi0.3)Sr2(Ca1-xLax)Cu2O6+σ system for 1.0≧x≧0.0 are discussed in detail. This system with the tetragonal HgBa2CaCu2O6-type (1212) structure was found only for x=0.25, 0.5 and 0.75. The a and c lattice parameters increase with the increasing La concentration due to the decreasing in oxidation state of Cu and the replacement of smaller Ca+2 ions (1.12 A) by larger La3+ ions (1.16 A). The transition temperature Tc decreases as the La substitution parameter x increase. We observed the maximal Tc at x=0.25 with 87K and 72K for x=0.5.

Hydrogen (H) absorption by YBa 2 Cu 3 O 7− δ (YBCO) was carried out by exposing the superconducting powders to rf-generated H plasma. We find that both the field-cooled (FC) and zero-field-cooled (ZFC) susceptibilities increase after hydrogenation. The largest enhancement is about 24% for the FC susceptibility at 5K.

The high quality Pr(Ba 2−x Sr x )Cu 3 O y (0 ≤ x ≤ 0.6) crystals with isostructural to R Ba 2 Cu 3 O y (R =Y or rare earth) compounds have been successfully prepared using a stoichiometrically melting growth method without flux. The x-ray diffraction patterns and rocking curves showed the well c-axis-oriented single-crystal nature of these specimens. The lattice parameter, degree of orientation, and crystallinity decrease with the substitution of Sr for Ba. No magnetic ordering was apparently observed in the series (x ≤ 0.6) by the all magnetization data between 5 K to 200 K and within ± 1 T. The χ ab −1 ( T ) with the applied field normal to c -axis have been fitted by simple Curie-Weiss law without considering the crystal field effect and shown the effective moments μ eff of 3.537 μ B for x = 0 and 3.572 μ B for x = 0.2, which is closely the Curie-Weiss moment value of free ion Pr 3+ .

Superconducting Bi-Pb-Ca-Sr-Cu-O oxides have been produced by the rapid thermal melt quenching method. The T c (ϱ mid· ) and T co (ϱ=0) of the as-melted glass sample sintered at 855°C for 24 hours in air were 110 K and 105 K, respectively. The specimen has a large diamagnetic shielding effect and high intragrain critical current density [J c (5K) ≈ 10 7 A/cm 2 at low field] compared with the conventional ceramic-sintered materials. The de Almeida-Thouless phase line (irreversibility line) H∗(T) is obtained by hysteresis curves.

(Tl0.5Pb0.5)Ca2Sr2Cu3Oy compound with Tco = 113 K has been achieved. The intragranular critical current density Jc at Ha = 1 T is estimated to be about 6 × 106 A/cm2 at 5 K and has a logarithmic temperature dependence below 40 K. An anomalous dimpling behavior occurs near the origin of the loop for powder sample. This Jc decreases slightly with magnetic field at low temperature and reaches a stable value at high field. The flux pinning centers may be considered as coming from the grain boundaries by the observation of the strong shielding effect and large hysteresis curves in bulk specimen compared with those in powder specimen.

Powder X-ray diffraction, low temperature electrical resistivity and magnetic susceptibility measurements have been made on new ternary cerium transition metal borides CeT 6 B 4 (≡ Ce 0.5 T 3 B 2 ) with the La 1- x Rh 3 B 2 -type structure, where T can be Ru, Rh or Ir. No isostructural compounds were found for T = Fe, Co, Ni, Os, Pd or Pt. Structural effect (disorder/vacancy) on valence fluctuations in these cerium compounds is discussed. These results, together with other results from ternary rare earth rhodium compounds RE 0.5 Rh 3 B 2 (RE = La to Lu, Y, Th), show interesting interplay among structural chemistry, valence fluctuations and long range magnetic order.

Copper 2P core level X-ray photoelectron spectra on several high Tc superconductors La1.85Ba0.15CuO4, Y1.2Ba0.8CuO4−δ and Y0.4B0.6CuO4−δ oxides have been measured. The results indicate the coexistence of Cu2+ and Cu3+ in these compounds.

We report the results of resistivity measurements in Y x Ba 1- x CuO 3-δ ( x = 0.3, 0.4, 0.5, 0.6). The x = 0.4 sample shows a superconducting transition at 96.7 K with a width of 1.6 K. Our X-ray analysis on the X = 0.4 sample indicates that the material exhibiting superconductivity is an orthorhombic perovskite phase with a = 3.894(1) A, b = 3.894(1) A, c = 11.682(2) A.