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排序方式: 共有339条查询结果,搜索用时 15 毫秒
71.
Svilen Bobev Eric D. Bauer John L. Sarrao Bernhard Eck 《Journal of solid state chemistry》2004,177(10):3545-3552
The Zintl compound EuGe2 crystallizes in the trigonal space group (No. 164) with the CeCd2-structure type. Its structure can be formally derived from the hexagonal AlB2-structure type by a strong puckering of the hexagonal layers. The chemical bonding in EuGe2 can be rationalized according to the Zintl concept as (Eu2+)(Ge1−)2, since the europium atoms are divalent and each germanium atom receives one additional valence electron. In that sense, EuGe2 is expected to be a closed-shell compound with semiconducting behavior. However, temperature dependent resistivity measurements show EuGe2 to be metallic. Subsequently, detailed crystallographic studies revealed the structure and the composition of EuGe2 to be free of defects and impurities, which, along with the confirmed divalent oxidation state of the europium atoms by means of magnetic measurements, make EuGe2 another example of a metallic Zintl phase. These results are in good agreement with the results of electronic structure calculations such as TB-LMTO-ASA (LDA) and FLAPW (GGA), which reveal non-zero DOS at the Fermi level. 相似文献
72.
《Current Applied Physics》2018,18(11):1205-1211
The frustrated magnet has been regarded as a system that could be a promising host material for the quantum spin liquid (QSL). However, it is difficult to determine the spin configuration and the corresponding mechanism in this system, because of its geometrical frustration (i.e., crystal structure and symmetry). Herein, we systematically investigate one of the geometrically frustrated magnets, the TbB4 compound. Using resonant soft x-ray scattering (RSXS), we explored its spin configuration, as well as Tb's quadrupole. Comprehensive evaluations of the temperature and photon energy/polarization dependences of the RSXS signals reveal the mechanism of spin reorientation upon cooling down, which is the sophisticated interplay between the Tb spin and the crystal symmetry rather than its orbit (quadrupole). Our results and their implications would further shed a light on the search for possible realization of QSL. 相似文献
73.
《Current Applied Physics》2015,15(12):1576-1579
Er3+/Yb3+-codoped SrMoO4 phosphors were prepared by a high-temperature solid-state reaction method. At room temperature, all the as-prepared samples exhibited strong upconversion properties and the emission intensity increased dramatically with the increase of Yb3+ ion concentration, reaching its maximum value when the concentration was 5 mol%. The dependence of emission intensity on the pump power suggested that the upconversion emission was a two-photon process. Furthermore, the optical temperature sensing properties based on green upconversion emissions of the SrMoO4:0.01Er3+/0.05Yb3+ phosphor were studied. It is found that the SrMoO4:0.01Er3+/0.05Yb3+ phosphor can be operated over a very wide temperature range of 93–773 K with a maximum sensitivity of ∼0.0128 K−1, indicating that low- and high-temperature thermometry can be simultaneously realized in this phosphor. 相似文献
74.
Rare-earth ammonium sulfate octahydrates of R2(SO4)3·(NH4)2SO4·8H2O (R=Pr, Nd, Sm, and Eu) were synthesized by a wet process, and the stable temperature region for the anhydrous R2(SO4)3·(NH4)2SO4 form was clarified by thermogravimetry/differential thermal analysis, infrared, Raman, and electrical conductivity measurements. Detailed characterization of these double salts demonstrated that the thermal stability of anhydrous R2(SO4)3·(NH4)2SO4 is different between the Pr, Nd salts and the Sm, Eu salts, and the thermal decomposition behavior of these salts was quite different from the previous reports. 相似文献
75.
R.K. Murakami H.R. Rechenberg A.C. Neiva F.P. Missell V. Villas-Boas 《Journal of magnetism and magnetic materials》2008,320(14):e65-e68
Effects of titanium carbide (TiC) addition on structural and magnetic properties of isotropic (Pr,Nd)–Fe-B nanocrystalline magnetic materials have been investigated. In this work, we investigate the effect of TiC addition on a (Pr,Nd)-poor and B-rich composition, as well as on a B-poor and (Nd,Pr)-rich composition. Rapidly solidified (Pr,Nd)–Fe–B alloys were prepared by melt-spinning. The compositions studied were (Pr1−xNdx)4Fe78B18 (x=0, 0.5, and 1) with addition of 3 at% TiC. Unlike the (PrxNd1−x)9.5Fe84.5B6 materials that present excellent values for coercive field and energy product, the (Pr,Nd)-poor and B-rich composition alloys with TiC addition present lower values. Rietveld analysis of X-ray data and Mössbauer spectroscopy revealed that samples are predominantly composed of Fe3B and -Fe. For the RE-rich compositions (PrxNd1−x)9.5Fe84.5B6 (x=0.1, 0.25, 0.5, 0.75, and 1) with the addition of 3 at% TiC, the highest coercive field and energy product (8.4 kOe and 14.4 MGOe, respectively) were obtained for the composition Pr9.5Fe84.5B6. 相似文献
76.
The samples of YBa3B9O18, LuBa3(BO3)3, α-YBa3(BO3)3 and LuBO3 powders have been synthesized by the solid-state reaction methods at high temperature and their X-ray excited luminescent properties were investigated. All the studied materials show a broad emission band in the wavelength range of 300-550 nm with the peak centers at about 385 nm for YBa3B9O18 and LuBa3(BO3)3, 415 nm for α-YBa3(BO3)3 and 360 nm for LuBO3 powders, respectively. Even though those compounds have the different atomic structures, they have the common structural feature of each yttrium or lutetium ion bonded to six separate BO3 groups, i.e., octahedral RE(BO3)6 (RE=Lu or Y) moiety. This octahedral RE(BO3)6(RE=Lu or Y) moiety seems to be an important structural element for efficient X-ray excited luminescence of those compounds, as are the edge-sharing octahedral TaO6 chains for tantalate emission. 相似文献
77.
稀土(Nd,Pr)(Ⅲ)双酞菁衍生物的合成,表征和气敏特性 总被引:3,自引:0,他引:3
合成了八-4-(四氢糖氧基)酞菁钕(Ⅲ)(A)、八-4-(β-萘氧基)酞菁钕(Ⅲ)(B)、八-4-(2,4-二叔戊基苯氧基)酞菁钕(Ⅲ)(C)和八-4-(2,4-二叔戊基苯氧基)酞菁镨(Ⅲ)(D)4种新的稀土(Nd、Pr)(Ⅲ)双酞菁衍生物,经元素分析、红外光谱、核磁共振谱表征。紫外可见光谱表明,它们在氯仿(10^-6mol/L)溶液中以单分子形式存在。热重分析证明配合物的热稳定性:B>C ̄D>A 相似文献
78.
Dominique Robert 《Journal of organometallic chemistry》2006,691(21):4393-4399
A series of yttrium and lutetium alkyl complexes [Ln(η5-C5Me4ZNR′-κN)(CH2SiMe3)(THF)n] (Ln = Y, Lu) was prepared by reacting the tris(trimethylsilylmethyl) precursor [Ln(CH2SiMe3)3(THF)2] with different linked amino-cyclopentadienes of the type (C5Me4H)ZNHR′ (Z = SiMe2, CH2SiMe2; R′ = tBu, Ph, C6H4-tBu-4, C6H4-nBu-4). The catalytic activity of these alkyl complexes in the hydrosilylation of 1-decene and styrene using PhSiH3 as reagent was examined under standard conditions. A significant influence of the ligand structure on the catalytic property (turnover frequency, regioselectivity) was observed with the yttrium complex [Y(η5-C5Me4CH2SiMe2NtBu-κN)(CH2SiMe3)(THF)] being the most active for 1-decene hydrosilylation. 相似文献
79.
Jens Niermann 《Journal of solid state chemistry》2004,177(7):2600-2609
The ternary aluminides R2Rh3Al9 (R=Y, La-Nd, Sm, Gd-Tm, Lu), R2Ir3Al9 (R=Y, La-Nd, Sm, Gd-Lu), and R2Pd3Al9 (R=Y, Gd-Tm) have been prepared by arc melting of the elemental components with an excess of aluminum and dissolving the aluminum-rich matrix in hydrochloric acid. They crystallize with Y2Co3Ga9-type structure: Cmcm, Z=4. The crystal structures of Ho2Rh3Al9 and Er2Ir3Al9 have been refined from single-crystal X-ray data; Ho2Rh3Al9: a=1316.8(3) pm, b=760.2(2) pm, c=933.7(2) pm, R=0.044 for 255 structure factors and 27 variables; Er2Ir3Al9: a=1313.8(2) pm, b=758.5(1) pm, c=933.8(2) pm, R=0.057 (392 F values, 27 variables). The structure may be viewed as consisting of atomic layers of the compositions A=R2Al3 and B=T3Al6 which alternate in the sequence ABAB along the z direction. Approximately 33% and 27% of the A layers were found to be misplaced in the crystals investigated for Ho2Rh3Al9 and Er2Ir3Al9, respectively. The magnetic properties of most iridium-containing compounds have been determined with a superconducting quantum interference device magnetometer. The yttrium and the lanthanum compounds show Pauli paramagnetism, others reflect the magnetic behavior of the rare-earth components. The magnetic ordering temperatures are all lower than 20 K. 相似文献
80.
A series of rare-earth iron borates having general formula LnFe3(BO3)4 (Ln=Y, La-Nd, Sm-Ho) were prepared and their magnetic properties have been investigated by the magnetic susceptibility, specific heat, and 57Fe Mössbauer spectrum measurements. These borates show antiferromagnetic transitions at low temperatures and their magnetic transition temperatures increase with decreasing Ln3+ ionic radius from 22 K for LaFe3(BO3)4 to 40 K for TbFe3(BO3)4. In addition, X-ray diffraction, specific heat, and differential thermal analysis (DTA) measurements indicate that the phase transition occurs for the LnFe3(BO3)4 compounds with Ln=Eu-Ho, Y, and its transition temperature increases remarkably with decreasing Ln3+ ionic radius from 88 K for Ln=Eu to 445 K for Ln=Y. 相似文献