T:Toxic;13765-24-7Relevant articles and documents
EPR characterization of O- and trapped electrons in 20% SrF2/SmOF
Au, Chak-Tong,Zhou, Xiao-Ping
, p. 1793 - 1798 (1996)
An X-ray diffraction study of the 20% SrF2/SmOF catalyst has revealed the presence of cubic SrF2 and rhombohedral SmOF crystal phases. The lattice of the SrF2 crystal phase was distorted. Cationic and anionic exchanges may have occurred to cause such deformity. When the 20% SrF2/SmOF sample was treated in helium at 1073 K, EPR signals corresponding to O- centres were observed. Hydrogen or ethane treatment of the sample at 973 K or above resulted in the detection of superhyperfine structures corresponding to the presence of trapped electrons. No similar EPR signals were observed on the SmOF sample. We suggest that these EPR-detectable species were located in the SrF2 lattice and existed largely in the bulk. The trapped electrons were stable in oxygen up to 673 K while O- centres were stable in ethane or hydrogen up to a temperature as high as 873 K. We speculate that the migration of O- centres and trapped electrons is more arduous in fluoride than in oxide. Hence the temperature for the combination of O- centres and trapped electrons as well as for the migration of O- centres and trapped electrons from the bulk towards the surface is higher in the former than in the latter.
Activation of O2 over SrF2- and BaF2-promoted SmOF catalysts for the oxidative dehydrogenation of ethane
Au, Chak-Tong,Zhou, Xiaoping
, p. 485 - 491 (1997)
Promotion of rhombohedral SmOF by SrF2 or BaF2 led to significant gain in ethane conversion but little change in ethene selectivity in the oxidative dehydrogenation of ethane. At 893 K, C2H6 conversion and C2H4 selectivity over SmOF were, respectively, 38.8 and 71.2%. With 10% SrF2/SmOF and 20% BaF2/SmOF catalysts, C2H6 conversion became 69.7 and 68.4%, respectively, while C2H4 selectivity was 67.7%. X-Ray diffraction (XRD) studies revealed a small amount of cubic SrF2 but no crystal phase of BaF2 in the promoted catalysts. The SrF2 lattice contracted slightly and the SmOF lattices expanded slightly. We believe that such deformities resulted from ionic exchange/substitution occurring between/within the SrF2 and SmOF phases with creation of active centres. The Raman and O2 temperature programmed desorption (TPD) results, indicated that, above 973 K, dioxygen species on SmOF were converted completely to mono-oxygen species. With the promoted catalysts, such conversion was complete at around 573 K. Because Sm3+ is paramagnetic and owing to the effect of spin-spin interaction, we could not obtain any EPR signals of O2- or O- over SmOF. Over the promoted catalysts, however, EPR signals corresponding to O2- and O- located in the proximity of non-paramagnetic Sr2+ and Ba2+ ions were observed. The conversion of O2- to O- was confirmed and monitored by EPR spectroscopy. We conclude that the deformities generated in the promoted catalysts have facilitated the conversion of dioxygen species to O- species at lower temperature, resulting in better catalytic performance.
The new carbodiimide Li2Gd2Sr(CN2) 5 having a crystal structure related to that of Gd 2(CN2)3
Unverfehrt, Leonid,Stroebele, Markus,Meyer, H.-Juergen
, p. 84 - 88 (2013/03/28)
The new carbodiimide compounds Li2RE2Sr(CN 2)5 (RE = Sm, Gd, Eu, Tb) were prepared by a straight forward solid state metathesis reaction of REF3, SrF2, and Li2(CN2) at around 600 °C. The crystal structure of Li2Gd2Sr(CN2)5 was solved based on X-ray single-crystal diffraction data. Corresponding Li2RE 2Sr(CN2)5 compounds were analyzed by isotypic indexing of their powder patterns. The crystal structure of Li 2Gd2Sr(CN2)5 can be well related to that of Gd2(CN2)3, because both structures are based on layered structures composed of close packed layers of [N=C=N] 2- sticks, alternating with layers of metal ions. The crystal structure of Li2Gd2Sr(CN2)5 can be considered to contain an ABC layer sequence of [N = C=N]2- layers with the interlayer voids being occupied by (three) distinct types of cations. Copyright
Preparation of REFeAsO1-xFx (R E=Sm and Gd) superconductors at a relatively low temperature
Cui,Chen,Cheng,Yang,Wang,Li,Zhao
, p. 449 - 452 (2011/07/07)
A series of the SmFeAsO1-xFx and GdFeAsO 1-xFx (x=0.05, 0.1, 0.15, 0.2, 0.25) samples have been prepared using nano-scaled ReF3 as the fluorine resource at a relatively low temperature. The samples have been sintered at 1100 and 1120 °C for SmFeAsO1-xFx and GdFeAsO1-xF x, respectively. These temperatures are at least 5060° lower than other previous reports. All of the so-prepared samples possess a tetragonal ZrCuSiAs-type structure. Dramatically supression of the lattice parameters and increase in Tc proved that this low temperature process was more effective to introduce fluorine into REFeAsO. Superconducting transition appeared at 39.5 K for SmFeAsO1-xFx with x=0.05 and at 22 K for GdFeAsO1-xFx with x=0.1. The highest Tc was detected to be 54 K in SmFeAsO0.8F0.2 and 40.2 K in GdFeAsO0.75F0.25. The use of the nano-scaled ReF3 compounds has improved the efficiency of the present low temperature method in synthesizing the fluorine-doped iron-based superconductors.
Synthesis and optical properties of non-stoichiometric lanthanide (Sm, Eu, Tm, Yb) fluorides
Ivanenko,Kompanichenko,Omelchuk,Zinchenko,Timukhin
, p. 841 - 847 (2010/09/17)
Nonstoichiometric samarium, europium, ytterbium, and thulium fluorides were prepared by reduction of the corresponding trifluorides with the same lanthanide metal or silicon. Crystal lattice type and lattice parameters of the compounds were determined by
Low temperature preparation and superconductivity of F-doped SmFeAsO
Chen,Cui,Cheng,Yang,Wang,Li,Zhang,Zhao
, p. 989 - 992 (2011/02/16)
A low temperature (1100 °C) process of preparing F-doped SmFeAsO samples has been developed using SmF3 with nanometer scale as the source of fluorine. A series of the SmFeAsO1 xFx (x = 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) samples have been prepared using the present method. Compared with previous reports, the present SmF3 is more effective to introduce F into SmFeAsO system in which a transition temperature of 39 K can be observed when x = 0.05. The superconductivity is definitely enhanced with the increasing F-doping level. All the samples presented to be layered structure and the crystal particle size is about three times larger with sintering time increasing from 36 h to 48 h. Except for the nanometer scale of SmF3, the flux effect of SmF3 is recognized to be another reason for the decrease of the sintering temperature. Further more, a relatively large amount of SmF3 was also employed in the raw materials to introduce excessive F and this has induced higher Tc (55 K) in SmFeAsO0.8F0.2+δ system.
The versatility of solid-state metathesis reactions: From rare earth fluorides to carboiimides
Unverfehrt, Leonid,Glaser, Jochen,Stroebele, Markus,Tragl, Sonja,Gibson, Katharina,Meyer, H.-Juergen
, p. 479 - 483 (2009/06/17)
The new carbodiimide compounds LaF(CN2) and LiPr 2F3(CN2)2 were obtained as crystalline powders by solid-state metathesis reactions from 1:1 molar ratios of REF3 (RE = rare earth) and Lisu
Synthesis and characterization of LnF(HF)(BF4)2 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy), and crystal structures of LnF(HF)(BF4)2 (Ln = Pr, Nd) and La(BF4) 3
Mazej, Zoran,Goreshnik, Evgeny,Hironaka, Kohei,Katayama, Yasushi,Hagiwara, Rika
, p. 2309 - 2315 (2010/03/30)
Rare earth trifluorides (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) react with boron trifluoride in anhydrous hydrogen fluoride (aHF) at room temperature. Products were found to be only sparingly soluble in aHF where the solubility decreases from lantha
Branched NaYF4 nanocrystals with luminescent properties
Liang, Xin,Wang, Xun,Zhuang, Jing,Peng, Qing,Li, Yadong
, p. 6050 - 6055 (2008/10/09)
In this article, branched NaYF4 nanocrystals have been successfully synthesized via a simple hydrothermal method. On the basis of the analysis of HRTEM and TEM images, the growth modes of the branched structure and further branching behavior have been proposed. The up- and down-conversion luminescence of branched NaYF4:Er3+/Yb3+ and NaYF4:Eu3+ have been characterized. Multiarmed NaYF 4 phosphors can be introduced into polystyrene to form composite luminescent polymers because of its special geometrical shape. In conclusion, the luminescent branched particles should be of wide potential application as building blocks in the future nanoscience and nanotechnology.
Synthesis and characterization of ternary NH4Ln 2F7 (Ln = Y, Ho, Er, Tm, Yb, Lu) nanocages
Liang, Xin,Wang, Xun,Wang, Leyu,Yan, Ruoxue,Peng, Qing,Li, Yadong
, p. 2186 - 2191 (2007/10/03)
In this paper, a new class of NH4Ln2F7 (Ln = Y, Ho, Er, Tm, Yb, Lu) inorganic nanocages that has been discovered will be presented. A facile template-free synthetic route was developed for one step, high yield, and large scale synthesis of ternary NH4Ln 2F7 (Ln = Y, Ho, Er, Tm, Yb, Lu) nanocages. On the basis of our studies, these nanocages are thermodynamically stable forms of this group of NH4Ln2F7 compounds. The tendency of NH 4Ln2F7 (Ln = Y, Ho, Er, Tm, Yb, Lu) to form these new-type nanostructures is believed to have a close relationship with their inherent layered structures, similar to that of inorganic fullerene-like nanoparticles. This new type of nanocage can be easily doped with other lanthanide ions, which may endow these nanocages with novel properties. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
