Crystal structure and physical properties of ternary compounds RPt3B, R=La, Pr, Nd

The crystal structure of a new series of ternary rare-earth platinum borides RPt₃B (R=La, Pr, Nd) has been studied by X-ray powder diffraction analyses from the ‘as-cast’ alloys. The tetragonal CePt₃B structure type, space group P4mm (No. 99), has been confirmed for all compounds. Rietveld refinements for the two compounds, PrPt₃B and NdPt₃B, were performed. LaPt₃B is a temperature-independent Pauli-type paramagnet from room temperature down to 4 K. PrPt₃B orders antiferromagnetically at T_N=15 K followed by a ferromagnetic spin flip at T_C=5 K, whereas NdPt₃B exhibits an antiferromagnetic spin alignment at a Néel temperature T_N=7 K. The temperature dependence of the electrical resistivity, ρ(T), reflects the metallic character of these compounds. Furthermore the characteristic changes of slope of ρ(T) plots prove the magnetic transitions.     

Crystal structures of R2Pd2Pb (R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) compounds

The crystal structures of the R₂Pd₂Pb (R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) compounds were determined using X-ray powder diffraction. The investigated compounds crystallize with Mo₂FeB₂ structure type (space group P4/mbm, Pearson code tP10). The importance of stabilization by polar intermetallic R–Pd bonding is underscored by a bonding analysis derived from electronic band structure calculations.     

The series LnSrVO4: synthesis, crystal structure, crystal chemistry and magnetic susceptibilities

The synthesis of several members of the series LnSrVO₄ can be achieved by hydrogen reduction of mixtures of Ln₂O₃, SrCO₃ and V₂O₅ or SrCO₃ and LnVO₄ at 1200 °C for 24 h. The series exists from lanthanum to terbium inclusive. The range of existence is discussed in terms of the ratio of radii of the structure fields and the large cation size mismatch ratios. Crystal structures were refined from powder neutron diffraction data for Ln La, Ce Pr and Nd. Cell constants are reported for all members from X-ray Guinier data. All compounds are isostructural with K₂NiF₄, I4/mmm. Magnetic susceptibility data from 4.2 K to 300 K are described. It is possible that a local moment of about 2.6 β per V³⁺ exists for Ln Ce, Pr and Nd but Ln La represents a different case.     

高温退火R0.67Mg0.33Ni3.0(R= La, Ce, Pr, Nd)贮氢合金电化学性能研究

采用Ce﹑Pr和Nd少量混合稀土部分替代La,采用感应熔炼及高温退火工艺制备(La0.7Ce0.1PrxNd0.2-x)0.67Mg0.33Ni3.0(x=0,0.1,0.2)系列贮氢合金。结果表明,与La0.67Mg0.33Ni3.0合金相比较,混合稀土元素加入后对合金的相组成没有本质影响,(La0.7Ce0.1PrxNd0.2-x)0.67Mg0.33Ni3.0(x=0,0.1,0.2)合金微观组织由主相PuNi3型结构与LaMgNi4第二相组成;随混合稀土加入和Pr含量x的增加,PuNi3型相晶体结构的晶胞体积和a轴减小,但c轴及轴比c/a增大。电化学性能测试结果表明,用混合稀土Ce﹑Pr和Nd少量替代La后均能明显改善合金的综合电化学性能,合金的电化学容量与La0.67Mg0.33Ni3.0合金(392.0mAh/g)比较虽略有下降,但随Pr含量x的增加,混合稀土合金电极容量有所提高(384mAh/g);经100次循环后,混合稀土合金电极容量保持率从La0.67Mg0.33Ni3.0合金时的64%提高到82%～83%,其高倍率放电性能则从78.4%提高到了89%～91%。     

Features of the HDDR process in R–Fe–B ferromagnetic alloys (R is a mixture of Nd, Pr, Ce, La, Dy and others)

Features of the conventional hydrogenation, disproportionation, desorption, recombination (HDDR) and solid-HDDR processes in some R–Fe–B (R is a mixture of Nd, Pr, Ce, La, Dy) ferromagnetic alloys were studied in the temperature range 20–990 °C and pressure range from 1×10⁻³ Pa to 0.1 MPa. This was carried out by means of differential thermal analysis (DTA), X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) methods. The hydride of the initial phase is formed by heating to 115 °C. The disproportionation of the alloys occurs in the temperature range from 320 to 800 °C. Φ-phase constitutes the base of the initial alloys. Among the disproportionation products, R-hydride, -Fe and two borides (Fe₂B and R_1.1Fe₄B₄) were revealed. The initial phase in all the alloys is recovered after heating in vacuum to a temperature of 990 °C. Full hydrogen desorption occurs in two temperature ranges with the peaks at 200–320 and 630–715 °C.     

Ce(Au,Sb)2 with UHg2 structure type, a new member of the AlB2 family

A new ternary compound Ce(Au,Sb)₂, with a homogeneity range has been observed from X-ray powder diffraction of as cast alloys, a = 4.743–4.712 Å, c = 3.567–3.768 Å. Its crystal structure was investigated by X-ray diffraction from Ce(Au_1−xSb_x)₂ (x = 0.266) single crystal: CAD-4 automatic diffractometer, Mo K radiation, a = 4.7256(6) Å, c = 3.6711(6) Å, P6/mmm space group, V = 70.997(17) Å³, Z = 1, ρ = 10.732 Mg/m³, μ = 76.369 mm⁻¹, R₁ = 0.0415, wR₂ = 0.0793 for 99 reflections with I > 2σ(I₀). The coordination polyhedron of X (X = 0.734Au + 0.266Sb) atom is a full-capped trigonal prism [XCe₆X₃X₂]. Ce atom is coordinated by 14 atoms: [CeX₁₂Ce₂]. The compound is isotypic with UHg₂ structure, a deformation derivative of AlB₂ structure type. It forms isostructural compounds with La and Pr.     

Magnetic and electrical properties of RCu5.1In6.9 compounds

Magnetic and electrical properties of the RCu_5.1In_6.9 compounds with R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er were investigated in the temperature range 4.2–300 K. Additionally, for the compounds of Gd, Tb and Dy exhibiting magnetic anomalies at low temperatures, the magnetization versus magnetic field up to 14 T was measured at 4.2 K. Investigated compounds follow the Curie–Weiss law with relatively small values of the paramagnetic Curie temperature and the values of effective magnetic moment being in fair agreement with the values for the free ions. The electrical resistivity exhibits metallic character. The results are discussed in terms of the differences and similarities with other rare earth intermetallics.     

稀土对La0.6R0.2Mg0.2（NiCoAlMn）3.3储氢合金相结构和电化学性能的影响

以La0.6R0.2Mg0.2Ni2.8Co0.2Al0.2Mn0.1(R=La、Ce、Pr、Nd、Y)合金为研究对象,研究稀土元素R部分替代La后对合金相结构和相组成及电化学性能的影响。X射线衍射(XRD)和显微电子探针(EPMA)方法分析结果表明,合金La0.8Mg0.2Ni2.8Co0.2Al0.2Mn0.1退火组织主要由Ce2Ni7型相(或Gd2Co7型)、PuNi3型相和CaCu5型相组成;Pr、Ce、Nd元素的替代对合金的相组成没有明显影响,而Y元素替代使合金中CaCu5型相明显减少,Ce2Ni7型(或Gd2Co7型)相显著增加,其相丰度达到79.03%。Y元素替代时合金中Gd2Co7型相基本消失。电化学测试和分析表明,稀土元素R替代La后对合金电极活化性能影响不大,其中Pr、Nd、Y部分替代La在一定程度上提高了合金的最大放电容量,而元素Y替代时合金电极容量最高达到392.6mAh/g;Y元素部分替代La使合金电极的循环稳定性得到明显提高,S100达到90.3%。     

Comparison of the spectroscopic behaviour of single crystals of lanthanide halides (X = Cl, Br)

Halides belong to large band gap matrices that have the perspective of wide applications when doped by optical active ions. This paper presents the results of spectroscopic studies of single crystals of halides (Cl, Br) of Ce, Pr and Nd. Their spectroscopic behaviour: electron–phonon coupling, ion pair interactions and the effect of covalency, is compared. Absorption, emission and emission excitation spectra of single crystals of LnCl₃·yH₂O (Ln = Nd, Pr, Ce; y=6, 7) were recorded at room temperatures and low temperatures down to 4.2 K. The intensities of the electronic lines and the Judd–Ofelt parameters were calculated (Nd, Pr) and compared to those of LnBr₃·yH₂O presented earlier by us. The relationship between the hypersensitivity and covalency was discussed. With increasing soft character of the halides (Br⁻ > Cl⁻), the covalent character of Ln–ligand bond increases and the hypersensitive bands become more intense. The Judd–Ofelt intensity analysis resulted in a set of τ_λ parameters evaluated with quite low standard deviations. The temperature dependences of the intensities have been found and the vibronic coupling in the f–f transitions were analysed. At the low temperature (4.2 K), strong vibronic components occur in the electronic lines of the Nd(III) and Pr(III) ions, mainly with the Ln–X vibrations. The modes, which are in resonance with the splitting of the ground state multiplet, mediate in the cooperative transitions.

Vibrational studies of the compounds under test were performed at the ambient temperature using IR and Raman spectroscopy. The assignment of the bands was done on the basis of the factor group analysis. The spectral features below 300 cm⁻¹ point at the differences between the spectra of the bromides and chlorides of Nd and Pr. Although the spectral features within the FIR region are complex, the bands of the praseodymium monocrystals originated by halogen bridges are clearly visible.     

Preparation and characterization of bis(dimolybdo-nonatungstogermanate)lanthanates of potassium

The heteropoly complexes K12[Ln(GeW9Mo2O39)2] · nH2O (Ln = La, Ce, Pr, Nd, and Sm) were prepared for the first time and characterized by chemical analysis, infrared (IR) spectrum, ultraviolet (UV) spectrum, X-ray powder diffraction, and thermal analysis. IR, UV spectra, and X-ray powder diffraction studies show that the structure of the heteropoly complexes is a square antiprism consisting of eight oxygen atoms of two GeW9Mo2O398-, heteropolyanions and a lanthanide ion. The thermostability of heteropoly complexes is lower than that of saturated Keggin structure dodecatungstogermanate.     

The magnetic structures of RMgSn compounds (R = Ce, Pr, Nd, Tb)

The synthesis of the new compounds RMgSn (R = La-Nd, Sm, Gd-Tm, Lu and Y) has been recently reported. The compounds formed by La and Ce crystallise in the TiNiSi structure type (oP12, Pnma), while from Nd they adopt the CeScSi-type (tI12, I4/mmm); PrMgSn is dimorphic: its high-temperature form (HT) is TiNiSi-type while the low-temperature one (LT) is CeScSi-type.In this paper we now report the results of a neutron diffraction investigation which has been performed in order to refine the crystal as well as the magnetic structures for the RMgSn compounds with R = Ce, Pr, Nd and Tb. All these compounds see at low temperature the establishment of long range magnetic ordering with a predominantly antiferromagnetic interaction; only PrMgSn-HT orders ferromagnetically. These results agree with those from magnetic measurements recently reported.The magnetic structure of CeMgSn is of the amplitude-modulated type, the value of the magnetic propagation vector refined at 2 K is τ = [0, 0.1886(4), 0.3384(8)]. The PrMgSn-HT phase below T = 52 K adopts first a purely ferromagnetic structure, then at about T = 15 K a second magnetic coupling leads to a spin-canted magnetic structure. Both PrMgSn-LT and NdMgSn have the same antiferromagnetic commensurate magnetic structure. The TbMgSn compound below T_N = 35 K orders antiferromagnetically with an equal moment cycloidal structure; however a second magnetic transition at a temperature corresponding to T_N2 = 65 K is likely also present.     

Magnetic and electronic properties of RCoxGe2 (R = Pr, Nd) compounds

Magnetization, magnetic susceptibility, neutron diffraction and X-ray photoemission spectroscopy measurements were performed on polycrystalline samples: PrCo_0.85Ge₂ and NdCo_0.82Ge₂, crystallizing in an orthorhombic structure of the CeNiSi₂-type. The magnetometric data indicate that both compounds are antiferromagnetic at low temperatures, PrCo_0.85Ge₂ below 5 K and NdCo_0.82Ge₂ below 2.1 K. The neutron diffraction data indicate an antiferromagnetic structure in PrCo_0.85Ge₂ at 1.5 K and give no evidence of any magnetic ordering in NdCo_0.82Ge₂. The X-ray photoemission data indicate that the valence bands are formed predominantly by R 4f5d6s and Co 3d bands. The spin-orbit splitting values determined from the Pr and Nd, 3d_5/2 and 3d_3/2 XPS spectra are equal to 20.9 eV for the Pr compound and 23.0 eV for the Nd compound. The analysis of these spectra performed on the basis of the Gunnarsson–Schönhammer model revealed a small hybridization between 4f-electrons of the rare earths with the conduction band which implies rather good stability of the f shell in these compounds.     

Crystal structure and its stability in CeCuAl3 single crystal

We present the crystal structure investigation of CeCuAl₃ compound. Our X-ray diffraction study confirms unambiguously BaNiSn₃-type structure as the crystal structure of CeCuAl₃ in whole temperature range. Moreover, phase transition around 300 °C was found by our high-temperature powder X-ray diffraction measurement. This transition preserves BaNiSn₃-type structure, only structural parameters change during the transition. The study is provided on single crystalline and polycrystalline samples as well as on La counterpart to compare mainly high-temperature behavior of these compounds.     

Structural investigation of ternary RIr3B2 compounds (R=Ce and Pr)

Structural studies were performed for the ternary RIr₃B₂ compounds (R=Ce and Pr) from as cast samples. The crystal structure of the ternary boride CeIr₃B₂ (CeCo₃B₂ structure type, space group P6/mmm, a=5.520(3) Å, c=3.066(2) Å, Z=1, V=80.91 ų, ρ_x=15.154 g cm⁻³) was refined to R₁=0.0470, wR₂=0.1240 from single-crystal X-ray diffraction data. The new ternary boride PrIr₃B₂ was found to be isostructural with the CeIr₃B₂ compound. Its lattice parameters a=5.5105(2) Å, c=3.1031(1) Å were obtained from a Rietveld refinement of X-ray powder diffraction data.     

Paramagnetic susceptibility simulations from crystal field effects on rare earth antimonates R3Sb5O12

The magnetic susceptibilities of polycrystalline rare earth antimonates R₃Sb₅O₁₂ (R=rare earth), with cubic structure, space group I43m (No. 217), where the point site symmetry of R is S₄, have been measured from 4.2 to 800 K. Using the wave functions and energy levels derived from standard free ion and crystal field parameters deduced from the analysis of the optical spectra of pure and/or doped Pr, Nd, Eu and Er compounds, the calculation of the temperature dependent paramagnetic susceptibility has been carried out according to the Van Vleck formalism. The same calculation through crystal field parameters resulting from the ab initio simple overlap model over the entire R₃Sb₅O₁₂ series has been performed. Curves of both kinds were very similar for each configuration, with the exception of those for the Pr compound. Very good agreements with experimental data are found, especially below around 400 K, even when the approximate D_2d (near S₄) potential is considered. The standard crystal field treatment of 4f^N configurations is shown to explain the magnetic properties of these compounds with no need to consider any sort of magnetic interaction between the magnetic ions.     

Preparation, thermal stability, and magnetic properties of Fe---Co---Zr---Mo---W---B bulk metallic glass

A bulk metallic glass (BMG) cylinder of Fe₆₀Co₈Zr₁₀Mo₅W₂B₁₅ with a diameter of 1.5 mm was prepared by copper mould casting of industrial raw materials. The amorphous state and the crystallization behavior were investigated by X-ray diffraction (XRD). The thermal stability parameters, such as glass transition temperature (T_g), crystallization temperature (T_x), supercooled liquid region (ΔT_x) between T_g and T_x, and reduced glass transition temperature T_rg (T_g/T_m) were measured by differential scanning calorimetry (DSC) to be 891, 950, 59 K, and 0.62, respectively. The crystallization process took place through a single stage, and involved crystallization of the phases -Fe, ZrFe₂, Fe₃B, MoB₂, Mo₂FeB₂, and an unknown phase, as determined by X-ray analysis of the sample annealed for 1.5 ks at 1023 K, 50 K above the DSC peak temperature of crystallization. Mössbauer spectroscopy was studied for this alloy. The spectra exhibit a broadened and asymmetric doublet-like structure that indicated paramagnetic behavior and a fully amorphous structure. -Fe was found in the amorphous matrix for a cylinder with a diameter of 2.5 mm. The success of synthesis of the Fe-based bulk metallic glass from industrial materials is important for the future progress in research and practical application of new bulk metallic glasses.     

UCo2Sn, UCo4Sn and UCo5Sn: a crystallographic and magnetic investigation

In our investigation of Co-rich alloys in the ternary U–Co–Sn system, we have identified three intermetallic compounds with composition UCo₂Sn, UCo₄Sn and UCo₅Sn, respectively. The existence and the crystal structure of the first compound, already known in the literature, have been confirmed, while the latter two compounds have been identified for the first time. The crystal structure of these compounds was determined by X-ray diffraction methods, performed both on powders (all samples) and single crystals (UCo₄Sn and UCo₅Sn). The crystal data are as follows (lattice constants from Guinier powder patterns): UCo₂Sn [UPd₂Sn-type, orthorhombic, oP16-Pnma, a = 9.402(3), b = 4.321(1), c = 6.615(2) Å], UCo₄Sn [MgCu₄Sn-type, cubic, , a = 6.992(2) Å] and UCo₅Sn [CeCu_4.38In_1.62-type, orthorhombic, oP56-Pnnm, a = 10.250(1), b = 16.012(2), c = 4.837(1) Å]. The physical properties of the compounds have been studied by electric transport (1.5–300 K), heat capacity (1.8–40 K) and magnetic measurements (1.8–300 K). The magnetisation data reveal weakly paramagnetic behaviour (with weak low temperature upturn due to parasitic impurity phases) in all the three alloys and absence of long-range magnetic ordering, despite the presence of uranium and a substantially high concentration of cobalt. The results for UCo₂Sn are in agreement with earlier reports in the literature. The magnitudes of the coefficients of the linear term in the heat capacity and the T² term in the low temperature resistivity track the room temperature magnetisation.     

Crystal structure and Rietveld refinement of the new ternary compound Al14Nd5Si

The new ternary compound Al14Nd5Si has been studied by means of the X-ray powder diffraction technique and the Rietveld method. The ternary compound Al14Nd5Si has a hexagonal Ni3Sn-type structure with space group P63/mmc (No.194), the lattice parameters are a = 0.64470 (2) nm and c = 0.45926 (1) nm. The Smith and Snyder figure of merit for the index, FN, is F30 = 97.8 (30). The X-ray diffraction data indicated that the crystal structure of the compound Al14Nd5Si has been successfully refined by the Rietveld method. The R-factors of Riet- veld refinement are Rp = 0.088 and Rwp = 0.120, respectively. The thermal dependence of magnetization for the compound was measured by a vibrating sample magnetometer. The experimentally determined magnetic effective paramagnetic moment is μeff = 3.60 μB per Nd atom. The paramagnetic Currie temperature θp = -33.7 K was also obtained from the Currie-Weiss law.     

A contribution to the crystallochemistry of ternary 1:1:1 and 1:1:2 rare earth intermetallic phases with Pb and Pd

The ternary alloys of the rare earths with lead and palladium were studied for the stoichiometric ratios 1:1:1 and 1:1:2 with respect to the structure of these alloys and their existence field. RPbPd (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb) compounds have a hexagonal structure, hP9 Fe₂P type, while RPbPd₂ (R = Pr, Sm, Gd, Tb, Dy, Ho, Er, Yb) alloys have the cubic AlCu₂Mn-type structure (cF16, BiF₃ superstructure).     

Crystallographic and magnetic properties of HfFe6Ge6-type REFe6Sn4Ge2 compounds (RE = Y, Gd–Er)

The REFe₆Sn₄Ge₂ (RE = Y, Gd–Er) compounds have been synthesized and studied by powder X-ray diffraction and magnetisation measurements. These compounds crystallize in the hexagonal HfFe₆Ge₆ structure although the parent ternary compounds REFe₆X₆ (X = Ge, Sn) display more complicated orthorhombic crystal structure. This evolution is discussed and interpreted on the basis of the relaxation of some RE–X contacts in the quaternary compounds. The iron sublattice order antiferromagnetically above room temperature (554 ≤ T_N ≤ 560 K) while the paramagnetic RE compounds display a second transition at low temperature (7.3 ≤ T_t ≤ 42.7 K). The magnetisation versus field curves display a metamagnetic behaviour at 4.2 K. The corresponding value of the magnetisation suggests a non-collinear ordering of the RE sublattice.