Role of rare-earth element oxides in catalysts for the oxidative conversion of methane based on Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

It has been established that oxides of the rare-earth elements with moderate redox potentials (La₂O₃, CeO₂) increased the activity and working stability of Ni-Al₂O₃/cordierite catalysts in the reactions of deep and partial oxidation of methane. In the presence of the (NiO + La₂O₃ + Al₂O₃)/cordierite catalyst the process of carbon dioxide conversion of methane can be intensified by introduction of oxygen into the reaction gas mixture which decreases the temperature to achieve high conversion to 75–100 °C and has practically no effect on selectivity with respect to H₂. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 6, pp. 359–364, November–December, 2008.     

A Mixed‐Ligand Approach for a Gigantic and Hollow Heterometallic Cage {Ni64RE96} for Gas Separation and Magnetic Cooling Applications

Nanosized aggregations of metal ions shielded by organic ligands possessing both exquisite structural aesthetics and intriguing properties are fundamentally interesting. Three isostructural gigantic transition‐metal–rare‐earth heterometallic coordination cages are reported, abbreviated as {Ni₆₄RE₉₆} (RE=Gd, Dy, and Y) and obtained by a mixed‐ligand approach, each possessing a cuboidal framework made of 160 metal ions and a nanosized spherical cavity in the center. Along with the structural novelty, these hollow cages show highly selective adsorptions for CO₂ over CH₄ or N₂ at ambient temperatures. Moreover, the gadolinium analogue exhibits large magnetocaloric effect at ultralow temperatures.     

Cathodoluminescence of Eu2+ in EuGa2S4 and Ga2S3:Eu2O3

We present the results of an investigation of the cathodoluminescence of the Eu²⁺ ion in gallium chalcogenides (Ga₂S₃) and europium thiogallate (EuGa₂S₄). We show that the intense wide-band radiation of these compounds is due to the 4f-5d transitions of the Eu²⁺ ions. With increase in the Eu²⁺ percent composition from 0.1 to 5.0 mol.% the luminescence brightness increases and then decreases. Translated from Zhurnal Prikladnoi Spektrskopii, Vol. 67, No. 2, pp. 268–270, March–April, 2000.     

钙钛矿Mn基氧化物的电子顺磁共振行为的实验研究

借助电子顺磁共振技术,对Mn³⁺/Mn⁴⁺=2∶1和1∶1的两个典型体系 在居里温度T_C以上温区的顺磁行为进行了实验研究.实验表明,存在一特征温度 T_min,通过该温度将T_C以上的磁行为分成两个明显可区分的温区： 在T_min以上,共振谱由一对称的单线构成,Lande 因子g值与温度无关且接近 自由电子的值(～20023),线宽随温度呈线性变化等;而在T_{min关键词： 稀土锰氧化物 电子顺磁共振 交换变窄 自旋-自旋相互作用 自旋-晶格相互作用}     

新型复合功能晶体Cd4TbO(BO3)3结构与性能研究

为探索新型复合功能晶体材料,采用高温固相反应法合成了Cd4TbO(BO3)3多晶粉末,并以NaF-B2O3为助熔剂生长出了小晶体.结构分析表明,Cd4TbO(BO3)3晶体属于单斜晶系,Cm空间群,晶胞常数为a=7.982(1) (A)、b=15.806(3) (A)、c=3.487(7) (A)、α=90°、β=100.57°、γ=90°,晶体中的阴离子基团为[BO3].测量了TG-DSC曲线、紫外可见透过光谱、红外光谱、拉曼光谱,并计算了晶体单位体积Tb的含量.结果表明, Cd4TbO(BO3)3晶体在500~1500 nm范围内透过率大于70;.Cd4TbO(BO3)3晶体单位体积含Tb量为4.624×1021/cm3,是磁光晶体TGG单位体积含Tb量的0.3倍.综上表明Cd4TbO(BO3)3是一种有前途的复合功能晶体材料.     

Full-profile fitting of emission spectrum to determine transition intensity parameters of Yb~(3+):GdTaO_4

The Judd-Ofelt theoretic transition intensity parameters A_(tp)~k of luminescence of rare-earth ions in solids are important for the quantitative analysis of luminescence.It is very difficult to determine them with emission or absorption spectra for a long time.A "full profile fitting" method to obtain A_(tp)~k in solids with its emission spectrum is proposed,in which the contribution of a radiative transition to the emission spectrum is expressed as the product of transition probability,line profile function,instrument measurement constant and transition center frequency or wavelength,and the whole experimental emission spectrum is the sum of all transitions.In this way,the emission spectrum is expressed as a function with the independent variables intensity parameters A_(tp)~k,full width at half maximum(FWHM) of profile functions,instrument measurement constant,wavelength,and the Huang-Rhys factor S if the lattice vibronic peaks in the emission spectrum should be considered.The ratios of the experimental to the calculated energy lifetimes are incorporated into the fitting function to remove the arbitrariness during fitting A_(tp)~k and other parameters.Employing this method obviates measurement of the absolute emission spectrum intensity.It also eliminates dependence upon the number of emission transition peaks.Every experiment point in emission spectra,which usually have at least hundreds of data points,is the function with variables A_(tp)~k and other parameters,so it is usually viable to determine A_(tp)~k and other parameters using a large number of experimental values.We applied this method to determine twenty-five A_(tp)~k of Yb~(3+) in GdTaO_4.The calculated and experiment energy lifetimes,experimental and calculated emission spectrum are very consistent,indicating that it is viable to obtain the transition intensity parameters of rare-earth ions in solids by a full profile fitting to the ions' emission spectrum.The calculated emission cross sections of Yb~(3+):GdTaO_4 also indicate that the F-L formula gives larger values in the wavelength range with reabsorption.     

Interplay of iron and rare-earth magnetic order in rare-earth iron pnictide superconductors under magnetic field

The magnetic properties of iron pnictide superconductors with magnetic rare-earth ions under strong magnetic field are investigated based on the cluster self-consistent field method. Starting from an effective Heisenberg model, we present the evolution of magnetic structures on magnetic field in RFeAsO(R = Ce, Pr, Nd, Sm, Gd, and Tb) and RFe_2As_2(R =Eu) compounds. It is found that spin-flop transition occurs in both rare-earth and iron layers under magnetic field, in good agreement with the experimental results. The interplay between rare-earth and iron spins plays a key role in the magneticfield-driven magnetic phase transition, which suggests that the rare-earth layers can modulate the magnetic behaviors of iron layers. In addition, the factors that affect the critical magnetic field for spin-flop transition are also discussed.     

稀土原子与离子的自然辐射寿命测量

概述了当前自由原子和离子的激发态自然辐射寿命测量技术的进展。以LaⅠ和PrⅡ为例,系统介绍了几种稀土元素自由原子和离子激发态寿命测量技术并分析了它们的优缺点;以SmⅡ为例,详细介绍了激光烧蚀产生自由原子(离子)技术及结合激光诱导荧光时间分辨光谱技术进行激发态寿命测量的优缺点。最后,探讨了改进上述技术局限性的解决思路,以期进一步提高辐射寿命测量的精确度。     

某些稀土氧化物的高温高压合成及其结构稳定性研究

 首次用高压高温方法，在3.2~4.0 GPa，1 000~1 300 ℃下，对CeO₂-R₂O₃（R=Eu，Gd），CeO₂-Tb₄O₁₁，Pr₆O₁₁-Tb₄O₇稀土氧化物进行合成实验，得到具有F型结构的CeEuO_3.5，CeGdO_3.5，CeTbO_3.5；B型结构的CeEuO₃，CeGdO₃，CeTbO₃，PrTbO₃和P型结构的PrTbO₃。PrTbO₃是迄今自然界尚未发现，文献未见报导过的新物质。对上面的产物和NdYbO₃、PrTmO₃，利用高、低温X射线衍射实验，检测了其结构的稳定性，结果指出：从300 ℃直到1 000 ℃，发生由B型CeRO_x向F型CeRO_x（R=Eu，Gd，Tb）、B型PrTbO₃向C型PrTbO₃的结构转变。F型CeRO_x属于氧缺位萤石型结构。