Transport,magnetic and thermodynamic properties of REPd2Ga3, RE = Pr,Nd, Sm

We present various investigations on the transport, magnetic and thermodynamic properties of the new ternary compounds REPd₂Ga₃ with RE = Pr, Nd, Sm. While PrPd₂Ga₃ does not show long-range magnetic order down to about 0.3 K, both NdPd₂Ga₃ and SmPd₂Ga₃ order magnetically. The latter exhibits a ferromagnetic ground state with weak ordered moments below T _c = 16.9 K and the former orders antiferromagnetically below T _N = 6.5 K with ordered Nd moments of 1.99(4) μ_B at saturation in the basal plane oriented perpendicular to the propagation vector k = [1/2, 0, 0]. The possibility of a Kondo type interaction in PrPd₂Ga₃ is discussed.     

Crystal chemistry and physical properties of the ternary compounds RE5B4C5 (RE=Ce,Pr, Nd)

The ternary rare-earth metal boride carbides RE₅B₄C₅ (RE=Ce, Pr, Nd) were prepared by arc melting the mixtures of the pure elements and subsequent annealing at 1270 K. Their crystal structures were determined from single crystal X-ray diffraction data. They crystallize in the Ce₅B₄C₅ type of structure (space group Pna2₁, Z=8). Two new compounds were found, Pr₅B₄C₅: a=24.592(2) Å, b=8.4563(5) Å, c=8.4918(5) Å, R₁=0.043 (wR₂=0.076) for 2871 reflections with I_o?2σ(I_o)); for Nd₅B₄C₅: a=24.301(1) Å, b=8.3126(5) Å, c=8.3545(4) Å, R₁=0.035 (wR₂=0.069) for 3707 reflections with I_o?2σ(I_o)). Its structural arrangement consists of a three-dimensional framework of rare-earth atoms resulting from the stacking of slightly corrugated two-dimensional square nets, leading to voids filled with B₄C₄, B₃C₃, BC₂ finite chains and isolated carbon atoms. Ce₅B₄C₅ is an antiferromagnet at 5 K followed by a metamagnetic transition in elevated external fields. Pr₅B₄C₅ and Nd₅B₄C₅ are ferromagnets below T_C=12 and 15 K, respectively.     

Transport properties and mangetoresistance of (RE,Sr)2NiO4 (RE=Pr,Nd, Sm and Eu)

We report on the crystal growth and the measurements of resistivity, magnetoresistance and photoemission spectroscopy of (RE,Sr)₂NiO₄ in the heavily Sr-doped region. Although the in-plane resistivity of the heavily Sr-doped crystals was rather small at room temperature, it increased for several orders of magnitude with decreasing temperature. A large negative magnetoresistance was observed for NdSrNiO₄ at low temperature, while only small magnetoresistance was observed for the single crystals of RE=Pr, Sm and Eu. Photoemission spectroscopy measurements revealed a significant influence of the RE 4f states to the electronic structure at relatively low binding energies in PrSrNiO₄ and NdSrNiO₄.     

First-principles investigations of the physical properties of RCd (R=Ce,La, Pr,Nd)

The crystal structural, electronic, elastic and the thermodynamic properties of RCd are investigated by using the first-principles plane-wave pseudopotential density function theory within the generalized gradient approximation (GGA). The calculated equilibrium lattice parameters for RCd are in good agreement with the available experimental data. Furthermore, the optical properties, namely the dielectric function, refractive index and electron energy loss are reported for radiation up to 30 eV. Finally, the elastic properties, the bulk modulus and the Debye temperature of RCd are given for reference.     

富稀土元素合金中镧,铈,镨,钕,钐测定方法的研究

本文用美国Jarrell-Ash 9000型多道光量计,采用无基体匹配法对富稀土元素合金中镧、铈、镨、钕、钐进行了测定分析。对稀土元素较复杂的光谱干扰运用元素间干扰系数和自身干扰系数校正法进行校正。对其非光谱干扰采取加入内参比进行补偿。通过人工合成样分析和实际富稀土元素合金样品加标准回收实验,表明干扰系数内参比法是一种有前途的无基体匹配的定量分析法。     

119Sn Mössbauer spectra of RMnSn2 intermetallics (R = La,Ce, Pr,Nd, Sm)

The ternary stannide series of RMnSn₂ compounds crystallize in the defect orthorhombic CeNiSi₂-type structure. They order magnetically close to room temperature. Isomer shifts are approximately 1.9 and 2.8 mm/s at the two tin sites, and there are transferred hyperfine fields of 3–6 T at 15 K, which depend on the rare-earth partner, especially at Sn₂ sites. The magnitude of the transferred hyperfine field per manganese neighbour is 4T.     

Structural and magnetic properties of RET2Sn2 compounds (RE=La,Ce, Sm; T=Ni,Cu)

The following compounds have been synthesized: LaCu₂Sn₂, CeCu₂Sn₂, SmCu₂Sn₂ and SmNi₂Sn₂. By means of X-ray diffraction their structure was determined to be primitive tetragonal of CaBe₂Ge₂-type (space group P4/nmm) and the lattice parameters were obtained.¹¹⁹Sn Mössbauer measurements were performed in a temperature range between 4.2 K and 300 K. The temperature dependence of the Lamb-Mössbauer factor reveals considerable softening of lattice vibration modes below 160 K. Only SmCu₂Sn₂ orders magnetically above 4.2 K.     

Electronic structure and magnetism of RPdIn compounds (R=La, Ce, Pr, Nd)

RPdIn (R = La-Nd) compounds were studied by means of magnetic susceptibility, specific heat and photoelectron spectroscopy measurements. The results prove that CePdIn is an antiferromagnetic Kondo lattice with T_N below 1.7 K. The Pr-based indide remains paramagnetic down to 1.7 K, and the lack of any magnetic ordering may be due to the presence of a singlet as the crystalline electric field ground state or/and strong hybridization between Pr 4f states and Pd 4d states. In turn, NdPdIn exhibits ferromagnetism below about 26 K. In contrast to CePdIn, for the Pr- and Nd-based compounds any significant enhancement of the electronic specific heat coefficient was observed.     

La、Ce、Pr-氟哌酸配合物的红外光谱研究

研究了镧、铈、镨与氟哌酸（NFA）形成的配合物的红外光谱，推测了配合物的结构。     

Growth and spectroscopic properties of RE, Mn:YAP (RE=Yb and Ce) photorefractive crystals

RE, Mn:YAP (RE=Yb and Ce) crystals with dimension of Φ 25×60 mm were successfully grown by the Czochralski method. The spectroscopic properties of RE, Mn:YAP (RE=Yb and Ce) crystals before and after γ-irradiation were investigated at room temperature. The results show that the content of Mn⁴⁺ ions was increased with the Yb³⁺ ions co-doping, but decreased by Ce³⁺ ions co-doping. Thermoluminescence (TL) spectra of the crystals indicate three steps of recombination, and the probable recombination processes were discussed.     

First-principles study on the crystal, electronic structure and mechanical properties of hexagonal Al3RE (RE = La, Ce, Pr, Nd, Sm, Gd) intermetallic compounds

The structural properties, elastic properties and electronic structures of hexagonal Al₃RE intermetallic compounds are calculated by using first-principles calculations based on density functional theory. Since there exists strong on-site Coulomb repulsion between the highly localized 4f electrons of RE atoms, we present a combination of the GGA and the LSDA+U approaches in order to obtain the appropriate results. The GGA calculated lattice constants for the hexagonal Al₃RE intermetallic compounds are in good agreement with available experimental values. The results of cohesive energy indicate that these compounds can be stable under absolute zero Kelvin and the stability of Al₃Gd is the strongest in all of the hexagonal Al₃RE compounds. The densities of states for GGA and LSDA+U approaches are also obtained for the Al₃RE intermetallic compounds. The mechanical properties are calculated from the GGA method in this paper. According to the computed single crystal elastic constants, Al₃La, Al₃Sm and Al₃Gd are mechanically unstable, while Al₃Ce, Al₃Pr and Al₃Nd are stable. The polycrystalline elastic modulus and Poisson’s ratio have been deduced by using Voigt-Reuss-Hill (VRH) approximations, and the calculated ratio of bulk modulus to shear modulus indicates that Al₃La compound is ductile material, but Al₃Ce, Al₃Pr, Al₃Nd, Al₃Sm and Al₃Gd are brittle materials.     

Glass formation and microstructure evolution in Al–Ni–RE (RE = La,Ce, Pr,Nd and misch metal) ternary systems

Glass formation has been systematically studied in melt-spun Al-rich Al–Ni–RE (RE?=?La, Ce, Pr, Nd and Mm; Mm?=?misch metal) alloys by navigating the compositions following the observation of microstructure evolution in the resulting ribbons. The optimum glass-forming regions are similarly located around Al₈₅Ni₁₀RE₅ and found in the centre of the composites with primary phase α-Al, Al₁₁RE₃ and Al₃Ni. The similarities in the critical cross-section below which a component is fully amorphous and the optimum compositions in these Al–Ni–RE systems are interpreted in terms of their competing crystalline phases and thermodynamic properties. Interestingly, it is indicated that Ni content is markedly higher than RE content in the best glass-forming alloys, which may be associated with strong interaction between Ni–Al atom pairs and the dense packing due to Ni-centred clusters.     

Quadrupole effects in the NMR spectra of 27Al in disordered mixed compounds CaREAlO4 (RE=La, Pr, Eu, Y)

The NMR spectra of ²⁷Al are measured in several disordered rare-earth aluminates CaREAlO₄. A change in the shape of the resonance line of the transition 1/2↔−1/2 in the transverse orientation in the rare-earth series RE=La, Pr, Eu, Y is observed, from a narrow (∼16 kHz), structureless line in the La compound to a wide (∼130 kHz), three-component line in the Y compound. This is attributed to a nonuniform distribution of the electric field gradient tensor at the ²⁷Al site. The electric field gradient tensor at the ²⁷Al site in a cluster (AlO₆)⁻⁹ is calculated by a nonempirical method (MO LCAO SCF) in the “deformable oxygen octahedron” model. The results are found to be in satisfactory agreement with the experimental values of 〈V _zz〉 and can be used to obtain the experimental splitting of the resonance line in the Y compounds for reasonable values of the parameters of the local deformations of the AlO₆ octahedron. The nature of the strong axial correlations in the distribution of the Ca and Y atoms in CaYAlO₄ is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 618–623 (April 1997)     

Superconductivity of F-substituted LnOBiS2 (Ln=La,Ce, Pr,Nd, Yb) compounds

Polycrystalline samples of F-substituted LnOBiS₂ (Ln?=?La, Ce, Pr, Nd, Yb) compounds were synthesized by solid-state reaction. The samples were characterized by X-ray diffraction measurements and found to have the ZrCuSiAs crystal structure. Electrical resistivity and magnetic susceptibility measurements were performed on all of the samples and specific heat measurements were made on those with Ln?=?La, Ce, and Yb. All of these compounds exhibit superconductivity in the range 1.9?K–5.4?K, which has not previously been reported for the compounds based on Ce, Pr, and Yb. The YbO_0.5F_0.5BiS₂ compound was also found to exhibit magnetic order at ～2.7?K that apparently coexists with superconductivity below 5.4?K.     

Dielectric and optical properties of Ln0.8Lu0.2TiNbO6 (Ln = Ce,Pr, Nd & Sm) ceramics

Ln_0.8Lu_0.2TiNbO₆ (Ln = Ce, Pr, Nd & Sm) are synthesized through conventional solid state ceramic route. The XRD, FT Raman and FT IR studies revealed that the samples have aeschynite orthorhombic symmetry. The samples are sintered at 1230 ^∘C. Using SEM technique, microstructure of the sintered samples is analyzed. The dielectric properties of all the samples in the radio as well as microwave frequencies are studied. UV spectra of the samples are recorded and the optical band gap is estimated from the Tauc's plots. The samples are found to be photoluminescent materials with emissions at violet and green regions.     

(REO)3BO3(RE=La、Gd、Y)中Pr3+的光致发光

研究了紫外光激发下,（ＲＥＯ）３ＢＯ３（ＲＥ＝Ｌa、Ｇd、Ｙ）基质中Ｐr＾３＋的光 谱性质;探讨了基质晶格、阳离子半径、Ｐr＾３＋－Ｏ＾２－键的共价性等因素对光谱性 质的影响;分析了Ｐr＾３＋的发光强度随组成变化的规律性及Ｐr＾３＋的＾３Ｐ１→＾３Ｆ２跃迁发射的自身浓度猝灭机理。