We have developed a synthetic route that uses sodium for the production of intermetallic Pt5Ce nanoparticles (ca. 6 nm average diameter) supported on carbon powder. Sodium melt was demonstrated to reduce a powder mixture of PtCl2 and CeCl3 to form submicrometer Pt5Ce particles with the simultaneous formation of NaCl. The NaCl–CeCl3 melt mixture and Na melt were formed during heating, which led to a
cubic C15 (MgCu 2 type) structure orders antiferromagnetically at 1.8 K. Single crystalline samples of Ce 1− x Pb x Pt 2 (0x . 5) have been prepared by the self-flux method. It is found that Pb atoms replace preferentially the Ce atoms in the face-center-cubic sublattice, forming a superlattice structure of the cubic C15b (MgSnCu 4 type). We have measured the specific heat, magnetic susceptibility, and
摘要 Laves 相化合物 CePt 2 以立方 C15(MgCu 2 型)结构结晶,在 1.8 K 下呈反铁磁性有序排列。通过自熔制备了 Ce 1− x Pb x Pt 2 (0 x . 5) 单晶样品方法。发现Pb原子优先取代面心立方亚晶格中的Ce原子,形成立方C15b(MgSnCu 4 型)的超晶格结构。我们测量了比热、磁化率和电阻率。结果表明,Ce 价数在 Ce 1− x Pb x Pt 2 ( x ⩽ 0.43) 中保持三价,但超晶格的形成抑制了 x = 0.43 时反铁磁有序温度低于 0.35 K。
Kristallstrukturen aus CaBe2Ge2- und CeMg2Si2-analogen Blöcken: Die PhosphideLnPt2P2−x (Ln: La, Sm)
作者:Anette Imre、Andrea Hellmann、Albrecht Mewis
DOI:10.1002/zaac.200700227
日期:2007.11
Crystal Structures of CaBe2Ge2 and CeMg2Si2 analogous Units: The Phosphides LnPt2P2−x (Ln: La, Sm) Single crystals of LaPt2P1.44 (a = 4.174(1), c = 19.212(5) A) were grown by reaction of vaporous phosphorus with LaPt2 at 1050 °C during two weeks, whereas SmPt2P1.50 (a = 4.131(1), c = 19.086(4) A) was synthesized by heating mixtures of the elements at 900 and 1100 °C (60 h) and annealing at 1050 °C
CaBe2Ge2 和 CeMg2Si2 类似单元的晶体结构: 磷化物 LnPt2P2-x (Ln: La, Sm) LaPt2P1.44 单晶 (a = 4.174(1), c = 19.212(5) A) 通过气相磷反应生长LaPt2 在 1050 °C 下持续两周,而 SmPt2P1.50 (a = 4.131(1), c = 19.086(4) A) 是通过在 900 和 1100 °C (60 h) 下加热元素混合物并退火合成的在 1050 °C (300 小时)。两种磷化物均通过单晶 X 射线方法进行研究。它们的晶体结构 (I4/mmm; Z = 4) 由 CaBe2Ge2 和 CeMg2Si2 类似单元沿 [001] 相互交替组成。P1 原子的位置被不完全占据,导致偏离 1:2:2 化学计量。通过 X 射线粉末衍射研究了另一种化合物 LnPt2P2-x,得到以下晶格常数:a =
Hydrogen absorbing characteristics of R–M (R=La, Ce; M=Co, Rh, Ir, Ni, Pd, Pt) binary systems
The capacity, rate and reversibility of the hydrogen absorbing/desorbing reaction have been measured for the binary systems composed of rare earth metal, R (La or Ce), and transition metal, M (Co, Rh, Ir, Ni, Pd or Pt), by Sieverts' method. These experimental results were discussed by comparing with the theoretical ones; density of states, cohesive energy and energy fluctuation, which were calculated by the extended Huckel method. Major results obtained are as follows. (1) The capacity of hydrogen absorption decreases almost linearly with increasing M components in R-M systems and it is explained in terms of the density of states. (2) The rate of hydrogen-absorbing reaction in La-M systems are larger than that of Ce-M systems. The larger absorption rate corresponds to the larger energy fluctuation. (3) The reversibility of the hydrogen absorbing/desorbing reaction is closely related with the cohesive energy of these systems. When the cohesive energy of the hydrogen absorbed system is large, a reverse (i.e. desorbing) reaction hardly occurs. (c) 2005 Elsevier B.V. All rights reserved.
Structure and magnetism in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">CePt</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>
作者:J. M. Lawrence、Y.-C. Chen、G. H. Kwei、M. F. Hundley、J. D. Thompson
DOI:10.1103/physrevb.56.5
日期:——
Neutron diffraction results for CePt2+x alloys with 0 less than or equal to x less than or equal to 1, combined with low resolution room temperature x-ray diffraction and electron microscopy, confirm that the alloys are single phase. The data dan be fit for all x with nearly equal agreement factors by structural refinements in either the C15 (MgCu2) phase br the C15b (AuBe5) structure. Observation of small peaks in the diffraction pattern for CePt, that are forbidden in C15 suggest that C15b is the correct structure for this composition (and possibly for the other alloy compositions); and application of Hamilton's test indicates that the C15b structure is preferred over the C15 to the 95% confidence level. Magnetic susceptibility and specific heat measurements indicate that the cerium is essentially localized and trivalent for all x. The antiferromagnetism observed for CePt, may be absent in the alloys, which behave as typical nonmagnetic cerium heavy fermion compounds with Kondo temperature T-K approximate to 2 K.