De nouveaux stannures ternaires de rhodium et d'elements des terres rares : TR2Rh3Sn5 OU TR = Y,Gd, Tb,Dy, Ho. structure cristalline et proprietes electriques et magnetiques de Y2Rh3Sn5

New ternary stannides are reported : RE₂Rh₃Sn₅ (RE = Y, Gd, Tb, Dy, Ho). Y₂Rh₃Sn₅ has been studied by single - crystal X-ray diffraction analysis. Its structure is of a new type with space group Cmc2₁ and Z = 4 : a = 4,387(2), b = 26,212(4), $\text{c}\text{= 7,1550(8)}\text{A}\text{?}$, D_x = 8,71 Mgm^?3, μ(AgK_α) = 17 mm^?1, F(000) = 1851, R = 0,045 for 478 independant reflexions (R_w = 0,046). This structure is characterized by a tridimensionnal lattice of RhSn covalent bonds with two very different sites for yttrium. Y₂Rh₃Sn₅ is diamagnetic and semimetallic according to its electrical properties.     

Low energy inert gas ion scattering from GdF3, Gd2O3 and Gd2 (MoO4)3 surfaces: 1. Inelastic effects

Inelastic effects in the scattering of Ar-40, Ne-20 and He-4 ions from GdF₃ and Gd₂O₃ have been studied. Such effects give rise to the low energy ‘tail’ of the elastic peaks in ion surface scattering (ISS). Experimental data show that the extent of ‘tailing’ increases from Ar-40 to He-4. For each probe ion type, the background is significantly greater in GdF₃ than in Gd₂O₃. The significance of (1) surface structure, (2) the surface polarization model and ion surface scattering, and (3) electronic effects on this low energy background will be shown by discussing the present data as well as supplementary results on He-4 ion scattering from selected oxides and $\text{polar}$ surfaces of Gd₂ (MoO₄)₃.     

Energy transfer in crystalline Er,Yb:Sc2O3

The use of Yb³⁺ as a sensitizer for Er³⁺ doped laser materials is a common technique because of the high Yb³⁺ absorption cross sections. Energy transfer processes from Yb³⁺ to Er³⁺ in Sc₂O₃ are studied by two different methods. Transfer parameters describing the interactions between Er³⁺ and Yb³⁺ ions are obtained on the one hand from the ratio of emitted photons around 1.55 μm by Er³⁺ ions and around 1 μm by Yb³⁺ ions at cw excitation of Yb³⁺, on the other hand by lifetime measurements of Yb³⁺ ions in the codoped samples. Laser experiments are performed to study the suitability of Er³⁺,Yb³⁺:Sc₂O₃ as a laser material. Comparisons with energy transfer in Er³⁺,Yb³⁺:glass are made.     

Vingt nouveaux germaniures ternaires TR5T4Ge10 de metaux tr des terres rares et T = Co,Rh, Ir. Supraconductivite de Lu5Rh4Ge10 et Lu5Ir4Ge10

Twenty ternary germanides, which crystallize in the Sc₅Co₄Si₁₀ type, have been prepared in the RE-T-Ge systems where RE is a rare earth and T = Co, Rh, Ir: with Co, RE = Tm-Lu; with Rh, RE = Y, Gd-Lu; with Ir, RE = Gd-Lu. Lu₅Rh₄Ge₁₀ and Lu₅Ir₄Ge₁₀ show superconducting transitions at 2.2?1.6 K and 2.01?1.94 K respectively.     

Structure cristalline de Mn0, 4Er4, 6S7

The crystal structure of Mn₀, ₄Er₄, ₆S₇ ($\text{a}\text{= 12,573 (4)}\text{A}\text{?}$, $\text{b}\text{= 11,390 (4)}\text{A}\text{?}$, $\text{c}\text{= 3,777 (4)}\text{A}\text{?}$, γ = 105,45°, space group B2/m, Z = 2) has been refined by a least square method to a final R = 0,045, with 1431 independant reflections. The octahedral positions are occupied either by Er and Mn atoms or by Er atoms only and the prismatic sites by Er atoms.     

High-pressure synthesis, electrical and magnetic properties of new filled skutterudites LnOs4P12 (Ln = Eu, Gd, Tb, Dy, Ho, Y)

New filled skutteudites LnOs₄P₁₂ (Ln: Eu, Gd, Tb, Dy, Ho and Y) have been prepared at high temperatures and at high pressures. X-ray diffraction of these compounds is studied at room temperature. The relationship between lattice constants and atomic numbers of lanthanide (including Y) is obtained for LnOs₄P₁₂ (Ln: lanthanide). Electrical and magnetic properties of the new filled skutterudites with heavier lanthanide have been investigated at low temperatures. EuOs₄P₁₂ and GdOs₄P₁₂ show ferromagnetic transitions at around 15 and 22 K, respectively. The valence states of both compounds are +2 for the Eu compound and +3 for the Gd compound. DyOs₄P₁₂ does not show the magnetic transition down to 2 K. However, a small electrical anomaly is found at around 10 K. YOs₄P₁₂ exhibits a superconducting transition at around 3 K. This compound is a new superconductor. Electrical and magnetic anomalies of new filled skutterudites with heavier lanthanide LnOs₄P₁₂ (Ln: Eu, Gd, Dy and Y) are discussed. We have also found the electrical anomaly based on the magnetic transition at around 22 K for GdFe₄P₁₂.     

RFe7Mn4Ti化合物的结构和磁性

利用真空电弧熔炼和真空热处理制备RFe7Mn4Ti(R=Y、Tb、Dy、Ho和Er)化合物样品。室温粉末样品的X射线衍射和热磁曲线测量表明：所有这些化合物都具有单ThMn12型结构．其晶格常数a、c和单胞体积V随着稀土元素的不同而变化。在DyFe7MmTi和HoFe7Mn4Ti化合物的热磁曲线上出现了明显的补偿特征．补偿温度分别约为123K和90K。本文还给出了这些化合物的居里温度和饱和磁化强度。     

De nouveaux isotypes lacunaires de CeNiSi2: Les germaniures RCoxGe2, R = Y, La-Sm, Gd-Lu, 0 < x 1

The new germanides RCo_xGe₂, R = Y, La-Sm, Gd-Lu, crystallize in the orthorhombic CeNiSi₂-type structure with cobalt vacancies. Their cobalt deficiency regularly increases through the series according to the lanthanide contraction: x vary from 1 to 0.34 between R = La and Lu. The structure of NdCo_0.83Ge₂ was refined from single-crystal data to a conventional R value of 0.034 for 210 independent reflections (R_w = 0.033). The La, Y and Lu compounds show Pauli paramagnetism and are not superconducting above 1.5 K.     

Growth and optical properties of Er,Yb:YAl3(BO3)4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl₃(BO₃)₄(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl₃(BO₃)₄ crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl₃(BO₃)₄ crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.     

Preparation and characterization of rare earth orthoborates, LnBO3 (Ln = Tb, La, Pr, Nd, Sm, Eu, Gd, Dy, Y) and LaBO3:Gd, Tb, Eu by metathesis reaction: ESR of LaBO3:Gd and luminescence of LaBO3:Tb, Eu

Lanthanide orthoborates of composition LnBO₃ (Ln = Tb, La, Pr, Nd, Sm, Eu, Gd, Dy, Y) and LaBO₃:Gd, Tb, Eu have been prepared by metathesis reaction. This method provides a convenient route for the synthesis of orthoborates and its solid solutions at low temperatures. Powder X-ray diffraction and FT-IR spectroscopy were used to characterize these borates. Rare earth borates, (LnBO₃) are isomorphous with different forms of CaCO₃ depending on the radius of rare earth ion. LaBO₃, LaBO₃:Gd, Tb, Eu, PrBO₃, NdBO₃ crystallized in aragonite structure, SmBO₃ crystallized in H-form and TbBO₃, EuBO₃, GdBO₃, DyBO₃, YBO₃ crystallized in vaterite structure. The structural analysis of TbBO₃ was carried out. The morphology of these borates was obtained from Scanning electron microscopy. Spin-Hamiltonian parameters for Gd³⁺ are deduced from room temperature electron spin resonance spectrum of LaBO₃:Gd. The luminescence of LaBO₃:Tb, Eu gave characteristics peaks corresponding to Tb³⁺, Eu³⁺ respectively.     

Reactions of hydrogen with R3Ni8Al intermetallides (R = Y,Pr, Nd,Gd, Tb,Dy, Ho,Er) with the Ce3Co8Si type of structure

Summary X-ray phase analysis, DTA, and volumetry have been applied to the reactions with hydrogen shown by R₃Ni₈Al compounds with structures of Ce₃Co₈Si type, where R = Y, Pr, Nd, Gd, Tb, Dy, Ho and Er. The R₃Ni₈Al react with hydrogen at room temperature and pressures below 0.1 MPa. Hydrides of composition R₃Ni₈AlH_x are obtained, where x=9.3 for Y, 10.3 for Pr, 11.4 for Nd, 8.7 for Gd, 6.9 for Tb, 5.7 for Dy, 5.4 for Ho, and 2.7 for Er. Hydride formation is accompanied by an increase in unit-cell volume by 5.7–18.2% without change in the initial hexagonal symmetry. Most of the hydrides decompose on heating at moderate temperatures up to 470 K. The main interest among these hydrides is in the Y₃Ni₅AlH_8.3, which can be recommended as a low-pressure hydrogen absorber.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 3, pp. 37–44, May–June, 1992.     

Properties of Gd2O3:Eu, Tb nanopowders obtained by sol-gel process

A significant practical application for nanostructured materials is X-ray medical imagery, because it is necessary to use dense materials in order to enable absorption of high energy photons. An important requirement of these materials is UV-vis range emission produced by X-ray excitation, which can be influenced by the particle size. Europium doped gadolinium oxide is a well known red phosphor. Moreover, nanophosphors of Gd₂O₃ codoped with Tb³⁺, Eu³⁺ increase their light yield by energy transfer between Tb³⁺ and Eu³⁺. In this study, Gd₂O₃ nanopowders codoped with Eu³⁺ and Tb³⁺ (2.5 at.% Eu³⁺, and 0.005 and 0.01 at.% Tb³⁺) were obtained via a sol-gel process using gadolinium pentanedionate as precursor and europium and terbium nitrates as doping sources. In this paper, we report the influence of annealing temperature on the structure, morphology and luminescent properties of Gd₂O₃:Eu³⁺, Tb³⁺ by means of TGA, XRD, TEM and X-ray emission measurements.     

White light upconversion of nanocrystalline Er/Tm/Yb doped tetragonal Gd4O3F6

Er³⁺, Tm³⁺ and Yb³⁺ codoped gadolinium oxyfluoride nanoparticles were prepared in aqueous solution by a simple coprecipitation method, under alkaline conditions. After a suitable heat treatment at 500 °C, the nanocrystalline powders were found to be single phase tetragonal Gd₄O₃F₆ after a structural characterization using X-ray powder diffraction. Transmission electron microscopy images showed that the average size of the nanoparticles was approximately 50 nm. Following appropriate lanthanide ion doping, the nanocrystals show bright white light upconversion upon excitation at 980 nm using a diode laser as the excitation source.     

Crystal growth and characterization of YAl3(BO3)4 doped with Sc, Ga, Pr, Ho, Tm, Yb

New data on flux growth of mixed crystals (Y,R)(Al,M)₃(BO₃)₄ (R=Pr, Ho, Yb, Tm; M=Sc, Ga) have been obtained. The average R distribution coefficients were found to be 0.53–1.02 for different rare earth elements as well as for scandium and gallium. Two morphological types of (Tm,Y)Al₃(BO₃)₄ crystals were characterized. The visible luminescence spectra of (Pr,Y)Al₃(BO₃)₄ and PrAl₃(BO₃)₄ at 10 K and room temperature were measured.     

Fluoride glasses in the system ZrF4 BaF2 RF3 (R = Gd,Yb)

The synthesis and properties of fluoride glasses in the system ZrF₄BaF₂GdF₃ (or YbF₃) are reported. Addition of fluorides of other elements, such as AlF₃, PbF₂, LaF₃ improve glass formation and prevent crystallization. Optical measurements show that these glasses transmit wavelengths up to 8 μm. Doping with PbF₂ increases the refractive index from 1.513 to 1.536.     

Etude structurale des phases Sc5,5Nb1,5O12 et Sc5,5Ta1,5O12. Ordre des cations dans les composes (A,B)7O12 de type Y6UO12

New phases Sc_5,5Nb_1,5O₁₂ and Sc_5,5Ta_1,5O₁₂ were prepared. Their structure is rhombohedral (space group R3, Z = 1) ($\text{a}\text{= 6,080}\text{A}\text{?}\text{α = 99°16}$ (niobate), $\text{a}\text{= 6,084}\text{A}\text{?}\text{α = 99°18}$ (tantalate). Many (A,B)₇O₁₂ ternary oxides have the same fluorite-related structure, the distortion from the cubic lattice depending upon ordering of cations on non-equivalent atomic positions. A sensitive influence of the degree of ordering is observed in the vibrational spectra of those phases.