Controllable synthesis of gadolinium tungstate nanoparticles with different surfactants by precipitation route

In this paper, gadolinium tungstate Gd₂(WO₄)₃ nanoparticles were synthesized via a new approach based on the reaction between gadolinium nitrate hexahydrate and Na₂WO₄.2H₂O in water.   Besides, three surfactants such as ethylene diaminetetraacetic acid (EDTA), sodium dodecyl sulfate (SDS), and polyvinylpyrrolidone (PVP) were used to investigate their effects on the morphology and particle size of Gd₂(WO₄)₃ nanoparticles. According to the vibrating sample magnetometer, gadolinium tungstate Gd₂(WO₄)₃ nanoparticles indicated a paramagnetic behavior at room temperature. The as-synthesized nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (UV–Vis), and energy dispersive X-ray microanalysis (EDX). To evaluate the catalytic properties of nanocrystalline gadolinium tungstate, the photocatalytic degradations of methyl orange under ultraviolet light irradiation were carried out.     

An electron microscope study of gadolinium iron garnet thin films prepared by the oxidation of vacuum evaporated metals

The oxidation of thin films of gadolinium, iron and Gd₃Fe₅ has been investigated by transmission electron microscopy and diffraction between 300 and 1200? C. The oxidation products for gadolinium and iron films are consistent with the oxidation mechanism proposed for bulk material. Thin films of Gd₃Fe₅ do not oxidize completely to give gadolinium iron garnet, high densities of garnet and orthoferrite inclusions are observed. An unusual form of grain growth is also observed in these films.     

Electrochemical preparation of metal cluster compounds

The electrochemical formation of low-valent cluster compounds is described. K₄Nb₆Cl₁₈ crystallizes on the cathode at 610°C, when an eutectic KiCl/KCl melt containing Nb₃Cl₈ is electrolysed with a niobium anode at 0.6 to 1.2 V cell voltage. Electrolysis of GdCl₃ at 770° yields h-GdCl both at the tantalum cathode and the gadolinium anode. Crystals of Gd₂Cl₃ form by the secondary reaction between GdCl and the GdCl₃ electrolyte upon slow cooling. The new cluster compound Gd₅Cl₉C₂ which contains interstitial C₂ units is formed, when a graphite crucible is serving as cathode.     

Enzyme-Triggered Transforming of Assembly Peptide-Modified Magnetic Resonance-Tuned Probe for Highly Sensitive Imaging of Bacterial Infection In Vivo

Confirming bacterial infection at an early stage and distinguishing between sterile inflammation and bacterial infection is still highly needed for efficient treatment. Here, in situ highly sensitive magnetic resonance imaging (MRI) bacterial infection in vivo based on a peptide-modified magnetic resonance tuning (MRET) probe (MPD-1) that responds to matrix metallopeptidase 2 (MMP-2) highly expressed in bacteria-infected microenvironments is achieved. MPD-1 is an assembly of magnetic nanoparticle (MNP) bearing with gadolinium ion (Gd³⁺) modified MMP-2-cleavable self-assembled peptide (P₁) and bacteria-targeting peptide (P), and it shows T₂-weighted signal due to the assemble of MNP and MRET ON phenomenon between MNP assembly and Gd³⁺. Once MPD-1 accumulates at the bacterially infected site, P₁ included in MPD-1 is cleaved explicitly by MMP-2, which triggers the T₂ contrast agent of MPD-1 to disassemble into the monomer of MNP, leading the recovery of T₁-weighted signal. Simultaneously, Gd³⁺ detaches from MNP, further enhancing the T₁-weighted signal due to MRET OFF. The sensitive MRI of Staphylococcus aureus (low to 10⁴ CFU) at the myositis site and accurate differentiation between sterile inflammation and bacterial infection based on the proposed MPD-1 probe suggests that this novel probe would be a promising candidate for efficiently detecting bacterial infection in vivo.     

Gadolinium doping of vanadate-tellurate glasses and glass ceramics

In order to further elucidate the local structure of ternary xGd₂O₃(100 − x)[0.7TeO₂ · 0.3V₂O₅] glasses with x = 0, 5, 10, 15, 20 mol%, FTIR spectroscopy, XRD diffraction and density measurement were performed. FTIR and density data show that by increasing the gadolinium ions content of the samples the excess of oxygen may be accommodated by the inter-conversion of some [VO₄] into [VO₅] structural units and of [TeO₃] into [TeO₄] units. The composition of the heat-treated glasses was found to consist mainly of the Te₂V₂O₉ crystalline phase. Varying x between 15 and 20 mol% Gd₂O₃ produces structural modification having as result an increase of the glass network polymerization degree. Accordingly, the gadolinium ions play a particular role related to the improvement of the homogeneity of the glasses and in accommodating the glass network with the excess of oxygen.     

Facile preparation of Gd3+ doped carbon quantum dots: Photoluminescence materials with magnetic resonance response as magnetic resonance/fluorescence bimodal probes

There are a few bimodal molecular imaging probes constructed by gadolinium (3+) ions in combination with carbon quantum dots (CQDs), and the reported ones show such obvious drawbacks as low luminous efficiency and weak MRI contrast. In the paper, a kind of CQDs photoluminescence materials with magnetic resonance response was prepared by hydrothermal method and employing gadopentetate monomeglumine (GdPM) as a precusor. Here, the GdPM plays a role of not only carbon source, but also gadolinium (3+) sources. When the GdPM aqueous solution with a concentration of 4 mg mL⁻¹ was pyrolyzed under 220 °C and 2.0 MPa for 8 h, an optimal CQDs was obtained which are doped with gadolinium (3+) ions in both chelates and Gd₂O₃ (named as Gd³⁺-CQDs). The average diameter of the Gd³⁺-CQDs is about 1.6 nm, which show a high photoluminescence quantum yield of 7.1%, as well as high longitudinal relaxivity (r₁) of 9.87 mM⁻¹ s⁻¹. And owing to the unconspicuous cell toxicity, the Gd³⁺-CQDs show big possibility for clinical application in magnetic resonance/fluorescence bimodal molecular imaging.     

Structural Defects in Tin-Doped Antimony Telluride Single Crystals

The structural perfection and homogeneity of Czochralski-grown Sb₂Te₃and Sb_1.96Sn_0.04Te₃crystals were characterized by transmission electron microscopy and electron probe x-ray microanalysis. The Sb, Sn, and Te core-level and valence-band x-ray photoelectron spectra were measured, and the corresponding binding energies were determined. The effect of Sn doping on the electronic structure and transport properties of the crystals was examined. The crystals were shown to be uniform in Sb : Te ratio and to have a relatively perfect structure. The dislocation density in the crystals was determined by electron microscopy and selective etching. The origin of the moiré patterns observed in electron micrographs was discussed. Sn doping of Sb₂Te₃was shown to produce no significant shifts of the core levels or changes in the electronic density of states in the valence band.     

Thermoelectric properties of Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> solid solutions prepared through melt solidification in liquids

Using scanning electron and optical microscopies, we have studied the morphology of fracture surfaces and microstructure of samples of an Sb₂Te₃–Bi₂Te₃ solid solution (p-type conductivity) prepared by hot pressing and extrusion of granules produced through melt solidification in liquids. All of the samples were found to contain an additional phase in the form of a tellurium-based eutectic, and their macroscopic structure was shown to depend on the granule comminution procedure. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the samples have been measured in the range 100–700 K. We have obtained materials with the highest dimensionless thermoelectric figure of merit ZT ~ 1.0 at temperatures from 300 to 440 K.     

Photoluminescence of Eu3+-activated GdTaO4 with both M type and M′ type structures

A series of Eu³⁺ doped M and M type gadolinium orthotantalate Gd_{1– x}Eu_xTaO₄ (x = 0–0.20) have been synthesized by high temperature solid state reaction. The emission and excitation spectra for M and M type gadolinium orthotantalate are studied in detail. The structural difference between M and M type structure obviously influences their luminescence properties. The main excitation bands in M type Gd_{1– x}Eu_xTaO₄ shift to shorter wavelength because of a shorter distance of Ta-O in comparison with M type. The strong evidence from excitation spectra, emission spectra and diffusive reflection spectra of these two system show Gd³⁺ can play an intermediate role of energy transfer in the process of luminescence. There is energy transfer from TaO₄ ^3– to Gd³⁺ and finally to Eu³⁺ via the charge transfer states and spectral overlap.     

Microstructure and phase transformations in a Ni<Subscript>50</Subscript>Mn<Subscript>29</Subscript>Ga<Subscript>16</Subscript>Gd<Subscript>5</Subscript> alloy with a high transformation temperature

A Heusler Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy with a high transformation temperature has been obtained by substituting 5 at% Gd for Ga in a ternary Ni₅₀Mn₂₉Ga₂₁ ferromagnetic shape memory alloy. The microstructure and phase transformations in the Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy have been investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. It is shown that the microstructure of the Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy consists of matrix and hexagonal Gd (Ni,Mn)₄Ga phase, which indicates a eutectic structure composed of these two phases. One-step thermoelastic martensitic transformation occurs in this quaternary alloy. Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy exhibits a martensite transformation start temperature up to 524 K, approximately 200 K higher than that of Ni₅₀Mn₂₉Ga₂₁ alloy. At room temperature, non-modulated martensite with twin substructure is observed in Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy.     

Phase diagram and out-of-equilibrium properties of melts in the As1bTe system

The As1bTe phase diagram is reexamined from D.T.A. measurements and from micrography. It shows two eutectic points and no miscibility gap. The role of the composition on both the viscosity and the interfacial tension in the liquid state is analysed from supercooling results and from the morphology of the crystallized phases. These parameters vary nonmonotonically between pure Te and As₂Te₃ definite compound, with extrema for the tellurium-rich eutectic composition. On the other hand, a small excess of arsenic in As₂Te₃ modifies drastically the properties of the melt. The consequences for the preparation of homogeneous As1bTe glasses are discussed. Finally a method is described for pulling large-size As₂Te₃ single crystals.     

Thermal conductivity of Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Gd<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> solid solutions

We have measured the thermal conductivity of Bi₂Te₃-Sb₂Te₃-Gd₂Te₃ solid solutions at temperatures from ～80 to 300 K and have determined the electronic and lattice components of their total thermal conductivity and the contributions of Sb₂Te₃ and Gd₂Te₃ to their thermal resistance. The results indicate that heat in these materials is transported largely by phonons and that three-phonon processes play a key role in determining the lattice thermal conductivity of the solid solutions.     

The phase diagram of the system tellurium/arsenic

Thermal analysis, metallographic and X-ray procedures have been used to investigate the system tellurium/arsenic. As₂Te₃ is the only binary compound present. It melts at 381° C and forms a eutectic with tellurium at 18.5 wt % As/81.5 wt % Te and at a temperature of 363° C. The As₂Te₃ and As also produce a eutectic at 31.5 wt % As/68.5 wt % Te, with a melting point of 380°C. The solid solubilities at the As and Te ends of ths phase diagram are too small to detect by the methods used, and the compositional range of the As₂Te₃ is very restricted.     

The crystallization of Gd2 3 -Al2O3 glasses

Glasses of Gd₂O₃ · x Al₂O₃ compositions where x represents 5/3, 4 and 6, were prepared using a rapid quenching apparatus and a laser beam. The crystallization process of the glasses was studied by means of differential thermal analysis (DTA), X-ray diffraction analysis and electron microscopy. The crystallizations of Gd₂O₃ · 5/3Al₂O₃, Gd₂O₃ · 4Al₂O₃ and Gd₂O₃ · 6Al₂O₃ are complex and exhibit one, two and three exothermic peaks in DTA measurement with increasing Al₂O₃ concentration, respectively. The crystallization process of Gd₂O₃ · 5/3Al₂O₃ glass involved the direct formation of the gadolinium aluminium garnet, 3Gd₂O₃ · 5l_{2 3} (GdAG), which is not obtained by the ordinary solid phase reaction. After crystallization of Gd₂O₃ · 4Al₂O₃ and Gd₂O₃ · l_{2 3} glass, both phases become a mixture of Gd₂O₃ · Al₂O₃ (perovskite type) and -Al₂O₃.     

Changes in Gd2O3 films grown on Si(100) as a function of nitridation temperature and Zr incorporation

We investigated Gd₂O₃ and Zr-incorporated Gd₂O₃ films grown on Si (100) as a function of nitridation temperature under an NH₃ ambient and the incorporation of Zr into the film. The formation of a silicide layer at the interfacial region was suppressed in cases of Zr-incorporated or NH₃-nitried Gd₂O₃ films. The crystalline structure was affected when zirconium, with a relatively small ionic radius, was substituted with gadolinium. When the concentration of Zr atoms in a Gd₂O₃ film reaches a specific level (Gd_0.6Zr_1.9O_4.3), phase transition occurred from cubic Gd₂O₃ to monoclinic ZrO₂. However, the monoclinic phase disappeared after nitridation at 900 °C in an NH₃ ambient. The majority of the nitrogen atoms accumulated near the interface in the films and the concentration of incorporated N increased with increasing Zr content and NH₃ annealing temperature. Moreover, nitrogen atoms bonded to Zr-silicate at the interface, in preference to ZrO₂ in the film. These incorporation characteristics of nitrogen into Zr-incorporated Gd₂O₃ film have an effect on the thermal stability and crystalline structure of a film.     

Safety assessment of nanoparamagnetic contrast agents with different coatings for molecular MRI

Despite the wide application of gadolinium as a contrast agent for magnetic resonance imaging (MRI), there is a serious lack of information on its toxicity. Gadolinium and gadolinium oxide (Gd-oxide) are used as contrast agents for magnetic resonance imaging (MRI). There are methods for reducing toxicity of these materials, such as core nanoparticles coating or conjugating. Therefore, for toxicity evaluation, we compared the viability of commercial contrast agents in MRI (Gd-DTPA) and three nanoparticles with the same core Gd₂O₃ and small particulate gadolinium oxide or SPGO (< 40 nm) but different coatings of diethyleneglycol (DEG) as Gd₂O₃-DEG and methoxy polyethylene glycol-silane (mPEG-silane: 550 and 2000 Dalton) as SPGO-mPEG-silane550 and SPGO-mPEG-silane2000, respectively, in the SK-MEL3 cell line, by light microscopy, MTT assay using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide, and the LDH assay detecting lactate dehydrogenase activity. The viability values were not statistically different between the three nanoparticles and Gd-DTPA. The MTT and LDH assay results showed that Gd₂O₃-DEG nanoparticles were more toxic than Gd-DTPA and other nanoparticles. Also, SPGO-mPEG-silane2000 was more biocompatible than other nanoparticles. The obtained results did not show any significant increase in cytotoxicity of the nanoparticles and Gd-DTPA, neither dose-dependent nor time-dependent. Therefore, DEG and PEG, due to their considerable properties and irregular sizes (different molecular weights), were selected as the useful surface covering materials of nanomagnetic particles that could reveal noticeable relaxivity and biocompatibility characteristics.     

Effect of gadolinia addition on varistor characteristics of vanadium oxide–doped zinc oxide ceramics

The effect of gadolinia addition on microstructure, electrical and dielectric characteristics, and aging behavior of vanadium oxide–doped zinc oxide varistor ceramics was systematically investigated. The average grain size decreased from 5.6 to 5.2 μm with an increase in the amount of Gd₂O₃ up to 0.1 mol%, whereas a further increase caused it to increase to 5.7 μm at 0.25 mol%. The sintered densities decreased from 5.51 to 5.44 g/cm³ with an increase in the amount of Gd₂O₃. With increasing the amount of Gd₂O₃, the breakdown field increased from 4,800 to 5,365 V/cm up to 0.05 mol%, whereas a further increase decreased it to 4,781 V/cm at 0.25 mol%. The varistor ceramics modified with 0.05 mol% Gd₂O₃ exhibited excellent nonlinear properties, with 66.1 in the nonlinear coefficient, whereas a further increase caused it to decrease to 17.6 at 0.25 mol%. The gadolinium acted like a donor, based on the electron concentration increasing from 4.20 × 10¹⁷/cm³ to 7.38 × 10¹⁷/cm³ with an increase in the amount of Gd₂O₃.     

Investigation of Ti-doped Gd2O3 charge trapping layer with HfO2 blocking oxide for memory application

In this study, Ti-doped gadolinium oxide (Gd₂TiO₅) is investigated by X-ray diffraction, atomic force microscopy, and capacitance voltage curves (C-V) as the charge trapping layer in metal-oxide-high-k material-oxide-silicon structure memories. It was found that the Gd₂TiO₅ charge-trapping layer with an HfO₂ blocking layer annealed at 900 °C had a larger window of 4.8 V in the C-V hysteresis loop, a faster program/erase speed and good retention without significant drift up to 10⁴ cycles. This excellent performance was attributed to the well-crystallized Gd₂TiO₅ structure and the higher probability of charges being trapped in the deep trap energy level of the Gd₂TiO_5. This Gd₂TiO₅ memory device with post-annealing shows considerable promise for use in future flash memory applications.     

Preparation of the Bi8Sb32Te60 solid solution by mechanical alloying

Bi₂Te₃, Sb₂Te₃ and Bi₈Sb₃₂Te₆₀ thermoelectric materials have been prepared by mechanical alloying using a high energy planetary ball mill. The alloy formation was followed by X-ray diffraction (XRD), the morphology by scanning electron microscopy (SEM) and the composition by electron microprobe. The samples of Bi₈Sb₃₂Te₆₀ were prepared in a reasonable milling time (less than 8 h) by mechanical alloying of binary alloys (Bi₂Te₃ and Sb₂Te₃). The single phase Bi₈Sb₃₂Te₆₀ solid solution obtained presents convenient stoichiometry and good homogeneity in composition. This revised version was published online in November 2006 with corrections to the Cover Date.