A new polymorph of Ln polysulfides (Ln = Pr and Nd)

A new polymorph of rare earth polysulfides was synthesized under high temperature-pressure conditions. Its X-ray diffraction patterns were indexed on an orthorhombic unit cell with the lattice constants of a = 0.8025, b = 1.6152 and c = 0.4062 for PrS₂ and a = 0.7977, b = 1.6012 and c = 0.4027 nm, for NdS₂. The calculated densities of the orthorhombic polysulfides are nearly same as those of the allotropic phases with monoclinic symmetry. To compare the stability of the two polymorphs, the Madelung energies of the structures were calculated and that of the monoclinic phase, which is synthesized without applying pressures, was found to be lower than that of the orthorhombic phase.     

Thermal Properties of Ln0.7Ca0.3CoO3 (Ln = La, Pr, and Nd) Perovskites

In this article, a detailed investigation of the thermal properties of doped perovskite cobaltates Ln_0.7Ca_0.3CoO₃ (Ln = La, Pr, and Nd) at temperatures 0 ${{\rm K} \leq T \leq}$ 350 K using the modified rigid ion model (MRIM) is presented. Theoretically, MRIM provides arguably the most realistic interaction potential to treat these properties. The variation of the specific heat and volumetric thermal expansion coefficient for these cobaltates in the temperature range 0 ${{\rm K} \leq T \leq}$ 350 K is computed. The computed specific heat is in reasonably good agreement with available experimental data. Present investigations reaffirm the presence of strong electron?Cphonon interactions in these compounds. The dominant contribution to the specific heat is the phonon term that follows here the Debye-type solid. In addition, the results on the temperature dependence of the molecular force constant (f), the reststrahlen frequency (??), the Debye temperature (?? _D), and the Gruneisen parameter (?? ₀) are also discussed.     

Low-frequency and microwave dielectric properties of Ba2LnTaO6 (Ln = La, Pr, Sm, Dy, Ce, Gd, Nd, Tm, Tb) ceramics

Nine Ba₂LnTaO₆ compounds are synthesized, and their low-frequency and microwave dielectric properties are studied. The results are analyzed in relation to earlier structural data and the ionic radius of Ln. The highest permittivity values are offered by the tantalates with the strongest distortion of the perovskite cell and the largest ionic radius of the lanthanide.     

K_2Ln(NO_3)_5·2H_2O(Ln=La,Ce,Pr,Nd,Sm)的晶体生长和热重-差热分析研究

本文生长出了K2Ln（NO3）5.2H2O（Ln=La；Ce；Pr；Nd；Sm）的单晶，并对其进行了晶体结构及差热-热重分析研究．结果表明，K2Ln（NO3）5.2H2O（Ln=La；Ce；Pr；Nd）的晶体属正交晶系，Fdd2空间群．首次生长出KPrN单晶并用直接法解出其晶体结构．解得KPrN的晶胞参数为：a=11．2210（10）,b=21．411（3），c=12．208（2）,Z=6；R=0．0240．对KLnN加热，则依次出现脱水、熔化、不可逆相变和NO的分解过程（K2Ce（NO3）5·2H2O除外）K2Ln（NO3）5·2H2O（Ln＝La；Nd；Sm）的NO分三步分解，K2Ln（NO3）5·2H。O（Ln=Ce；Pr）的NO分两步分解·KNO3和Ln（NO3）3·nH2O的混合物在225℃左右生成K2Ln（NO3）5     

New rare-earth double-layered-perovskite oxyfluorides, RbLnTiNbO6F (Ln = La, Pr, Nd)

New Dion-Jacobson-type double-layered oxyfluoride perovskites, RbLnTiNbO₆F (Ln=La, Pr, Nd), have been synthesized. Rietveld refinement of X-ray powder diffraction data (space group P4/mmm) shows the compounds to be isostructural with RbSrNb₂O₆F. Curie-Weiss behavior is observed in the Pr, Nd compounds. This series further illuminates the substitutional variations, both cationic and anionic, that can be achieved within the RbLaNb₂O₇ structure type.     

Influence of lead oxide addition on LnTiTaO<Subscript>6</Subscript> (Ln = Ce,Pr and Nd) microwave ceramics

The effect of PbO addition on the structural, processing and microwave dielectric properties of LnTiTaO₆ (Ln = Ce, Pr and Nd) ceramics are reported. Conventional solid state ceramic route was used for the preparation of samples. Phase pure LnTiTaO₆ (Ln = Ce, Pr and Nd) ceramics are prepared at a calcination temperature of 1300°C. The samples are sintered at optimized temperatures. Addition of PbO reduces the sintering temperature. The crystal structure of the materials was analysed using X-ray diffraction techniques and the surface morphology of the sintered samples was analysed using scanning electron microscopy. The dielectric constant at microwave frequency range decreases for higher PbO addition for all the samples but the quality factor improves on small PbO addition. The thermal stability of resonant frequency was also improved with PbO addition on all the systems. A number of samples with improved microwave dielectric properties were obtained on all the systems suitable for practical applications.     

Preparation, characterization and dielectric properties of Ba3Ln3Ti5Nb5O30 (Ln=La, Nd) ceramics

Ba₃Ln₃Ti₅Nb₅O₃₀ (Ln=La, Nd) ceramics were prepared by the conventional solid-state ceramic route. The sintered samples were characterized by X-ray diffraction and scanning electron microscopy (SEM) methods. They have high dielectric constants, 141 and 203 at 13 MHz for La-based and Nd-based ceramics, respectively. The loss factor of the ceramics increases with frequency.     

Synthesis of the LnNb7O12 (Ln = La, Ce, Pr) Discrete-cluster compounds

The new compounds CeNb₇O₁₂ and PrNb₇O₁₂, isostructural with LaNb₇O₁₂, have been synthesized and characterized by x-ray diffraction. The structures of the LnNb₇O₁₂ (Ln = La, Ce, Pr) compounds have space group P2₁/c (Z = 4), with lattice parameters a = 10.764(2), 10.743(2), 10.738(4) Å; b = 9.192(2), 9.146(2), 9.137(3) Å; c = 10.313(2), 10.304(2), 10.303(3) Å; and β = 104.25(2)°, 104.31(2)°, and 104.21(3)°, respectively. The reduction in the lattice parameters of LnNb₇O₁₂ in going from La to Pr correlates with the ionic radii of Ln: r(La³⁺) > r(Ce³⁺) > r(Pr³⁺). In the Nd(Sm)-Nb-O systems, phases of stoichiometry LnNb₇O₁₂ have not been obtained.     

Anion disorder in LnF<Subscript>3</Subscript> (Ln = La,Ce, Pr) crystals

The mechanism of lattice “melting” in tysonite-structure superionic trifluorides is analyzed in relation to the structure of LaF₃ crystals. The ion displacements within the unit cell are shown to correlate with the dynamics of the Raman scattering parameters of the crystals. The frequency and intensity of the lines at 370, 392 (LaF₃), 376, and 404 cm⁻¹ (PrF₃) show anomalous behavior in three temperature ranges: 160–180, 240–280, and 420–460 K. The anomalies in the two higher temperature ranges are due to lattice disordering in the superionic transition region. The scattering in the range 160–180 K is tentatively attributed to fluoride ion displacements in split sites with a few potential wells. It is shown based on a split-site model that the thermally activated formation of interstices comparable in size to the mobile fluoride ion is an inherent feature of the LnF₃ structure.     

复合氧化物Ln0.67Sr0.33MnO3（Ln=La,Pr,Nd,Sm）的制备,结构与电性

本语文通过共沉淀工艺合成了复合氧化物Ｌｎ０．６７Ｓｒ０．３３ＭｎＯ３（Ｌｎ＝Ｌａ、Ｐｒ、Ｎｄ、Ｓｍ）与传统陶瓷制备方法相比，成相温度降低约４５０℃，经Ｘ射线衍射分析表明，所得复合氧化物为立方钙钛矿结构，晶胞参数随稀土离子半径变化而呈规律性变化，样品的四极法电阻率测试结果表明；样品中的稀土离子Ｌｎ的离子半径对其本身的地电性起决定性的作用，应用双交换理论，样品中的稀土离子Ｌｎ的离子半径对其本身的导电性     

Lattice Effect on Magnetic and Electrical Properties of Ln2/3Pb1/3MnO3 （Ln=La,Pr, Nd） Films

Lattice effect on magnetic and electrical transport properties of Ln2/3Pb1/3MnO3 （Ln=La, Pr, Nd） films prepared by RF magnetron sputtering technique were investigated. With the decrease of the average ions radius 〈rA〉, the structure of Ln2/3Pb1/3MnO3 （Ln=La, Pr, Nd） targets transit from the rhombohedral phase to the orthorhombic phase, and the Curie temperature reduces rapidly with the decrease of 〈rA〉. The electrical properties show that films are the metallic state which can be fitted to the formula： ρ（T）=ρ0 ＋ ρ1T^2 ＋ ρ2T^4.5 at low temperatures. The temperature range of the ferromagnetic metallic state becomes narrow with the decrease of 〈rA〉. The phenomenon can be explained by the lattice effect.     

Preparation, characterization and dielectric properties of Sr5LnTi3Ta7O30 (Ln=La, Nd) ceramics

Sr₅LnTi₃Ta₇O₃₀ (Ln=La, Nd) ceramics were prepared by the conventional high temperature solid state reaction route. The sintered samples were characterized by X-ray diffraction and scanning electron microscopy methods. SLTT and SNTT belong to paraelectric phases of filled tetragonal TB structure at room temperature. SLTT and SNTT ceramics show high dielectric constant of 131 and 116 together with low dielectric loss 0.008 and 0.0036 at 1 MHz, respectively. In comparison with Ba-based ceramics with TB structure, the temperature coefficients of the dielectric constant () are significantly reduced.     

Preparation of sub-micrometer LnPO4 particles (Ln = La, Ce)

Sub-micrometer LnPO₄ particles (Ln = La, Ce) are prepared by heating of Ln(CH₃COO)₃ · 2H₂O and (NH₄)H₂PO₄ in diethylene glycol (DEG) at 180°C. Based on this so-called polyol method, spherical LnPO₄ particles 30 to 180 nm in size can be realised. According to X-ray powder diffraction patterns, the phosphates turn out to be highly crystalline right after preparation. The particle size is investigated with scanning electron microscopy in the powder state as well as with laser diffraction methods in the DEG suspension. Furthermore, the agglomeration behaviour of the phosphate particles in DEG suspension after mixing with water and the properties of re-suspended powder material in water is studied.