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We report a structural study of the stuffed pyrochlore series Ln2(Ti2−xLnx)O7−x/2 (Ln=Ho, Yb; 0?x?0.67). Electron microscopy and Rietveld refinements of neutron powder diffraction data for the x=0.67 end members, Ho2TiO5 and Yb2TiO5, reveal that small domains (∼50 Å or less) exist where the Ln and Ti/Ln sublattices are pyrochlore like, while the average structure is fluorite like. Both the Ho and Yb stuffed pyrochlore series for 0.1?x?0.5 are shown to be a composite of long- and short-range-ordered pyrochlore phases. The relative fraction of long-range vs. short-range pyrochlore order decreases with increasing Ln doping. An additional complex structural modulation of the pyrochlore structure is observed in electron diffraction and high-resolution electron microscopy images. 相似文献
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Rare earth orthovanadates, REVO4, having the zircon structure, form a series of materials interesting for magnetic, optical, sensor, and electronic applications. Enthalpies of formation of REVO4 compounds (RE=Sc, Y, Ce-Nd, Sm-Tm, Lu) were determined by oxide melt solution calorimetry in lead borate (2PbO·2B2O3) solvent at 1075 K. The enthalpies of formation from oxide components become more negative with increasing RE ionic radius. This trend is similar to that obtained for the rare earth phosphates. 相似文献
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采用共沉淀法和浸渍法在不同条件下制备了稀土-SO42-/ZrO2系列固体酸催化剂。使用废油脂与甲醇的酯交换反应评价了催化剂活性,并通过X射线衍射、红外光谱、比表面积测定表征方法考察了催化剂结构和性能的关系。结果表明,La摩尔掺杂量4%、焙烧温度600℃时制得的SO42-/ZrO2-La2O3催化剂活性最高,此时脂肪酸甲酯的产率为64.68%,且具有较好的重复使用性。稀土的引入使活性四方相ZrO2更加稳定,600℃焙烧使催化剂既具有较多活性四方相ZrO2,又具有较大比表面积,从而提高了催化剂活性。催化剂中形成了固体超强酸结构,且改性后酸强度增大,催化剂活性中心数目增加。 相似文献
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The on-line column preconcentration technique with inductively coupled plasma optical emission spectroscopy (ICP–OES) has been developed using a cartridge filled with octadecyl silica modified by l-(2-pyridylazo) 2-naphtol (PAN). The aim of this method was to determine some rare earth elements (REEs) (Ce, Dy, La, Sm, and Y) and uranium in water samples. Sample solutions were passed through the C18-modified column. The adsorbed cations were subsequently eluted from the column and transferred into the plasma with nitric acid solution for simultaneous determination of them. Sample pH, amount of PAN as a complexing agent, sampling and eluting flowrates and concentration of the eluent were optimized. Detection limits based on three times of standard deviations of blank by 10 replicates were in the range of 11 ng l−1 for Dy to 69 ng l−1 for U. Sample throughput was 10 samples h−1. The proposed method was applied to determine REEs in natural water samples. Recoveries of the REEs from natural water samples were between 95 and 106% with percent relative standard deviation (%R.S.D.) of 1.0–7.9%. 相似文献
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