The crystal structures of the "hectoborides" NdB65 and ThB60 have been elucidated from single crystal X-ray structure determination supported by TEM-SAED analyses. Both compounds crystallize in a face-centred cubic lattice with space group Fm (3) over barc (No. 226) (a(NdB65) = 2.35385(4) nm, R-F = 0.0491; a(ThB60) = 2.35170(5) nm, R-F = 0.0489) isotypic with the aristo-type of hectoborides, namely YB66. With respect to the structure type of YB66 in its original version by Richards and Kaspar [2], we observe for both compounds, NdB65 and ThB60, a split position (total occupancies 0.5) for the metal atoms in site 48f as well as a second metal atom position in site 8a at a reduced occupancy; furthermore, we only arrive at seven B-sites 192j and 5 B-sites 96i, but did not find a B-atom (B13) in site 64g (x = 0.23, x, x). In contrast to the earlier structure determination of ThB66(O) [11] our WDX analysis did not present any hints for oxygen contamination, therefore site 8a (1/4,1/4,1/4) hosts a Th atom at low occupancy of 0.12(1) Th instead. Similarly, the 8a site is also partially occupied by 0.04(1) Nd in NdB65. Whereas the present investigation removes all doubts on the formation of NdB65 (YB66-type), our analysis did not reveal the formation of isotypic "PrB66". On the basis of our SEM data, revised phase relations for the three systems Nd-B, Pr-B and Th-B have been designed for the boron-rich part (>85 at.% B). Whereas at room temperature hardness of ThB60 (23.8 GPa) and for NdB65 (24.3 GPa) fit well among hardness data for the corresponding rare earths hectoborides, the by-product material ThB99 (beta B-type) with 42 GPa is a superhard material.

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Heat capacity data of U3Al2Si3 single crystal exhibit a maximum at 38 K connected with a transition to a magnetically ordered state. For a full description of the electron part we used y(0) = 145 mJ/mol K-2 and for the phonon part of the specific heat we used the harmonic approximation of the phonon spectrum including both the Debye model with T-D = 296 K and the Einstein model with T-E = 136, 249 and 438 K. The heat capacity data below the magnetic transition down to 2 K fit very well within the model introducing the energy gap Delta = 39 K in the dispersion relation of magnons. An upturn of the C/T(T) curve, found below T = 2 K, can not be fully attributed to the nuclear Schottky contribution. The electronic heat capacity coefficient (y approximate to 230 mJ/mol K-2 is enhanced and varies between 0.15 K and 12 K as the square root of T. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Publisher Summary This chapter discusses the phase equilibria in ternary and higher order systems with rare earth elements and silicon. The present status of information about phase equilibria and formation of ternary metal silicides with R elements (R = Sc, Y, and the lanthanides) is summarized. Phase equilibria have been investigated for only a small number of the possible ternary combinations R–M–Si, and for a larger number of ternary systems only a few compounds have been identified to date. Rare-earth-metal-silicon ternary phase diagrams are listed in alphabetical order of the chemical symbol of the rare earth element (Ce, Dr, Er,…,Yb). Under each rare earth the systems are listed alphabetically by the chemical symbol of the non-rare-earth element. Phase equilibria in the system Ce–Fe–Si were determined in two partial isothermal sections, at 800°C for the region 0 33 a/o Ce, and at 400°C for the region 33-100 a/o Ce, by means of X-ray and metallographic analysis of 125 alloys. The phase equilibria in the ternary system Ce-Gd-Si have been established by means of X-ray and metallographic analysis of 105 alloys prepared by arc melting and subsequent annealing in evacuated silica capsules for 800 h at 600°C.

AbstractDie aus den Elementen erhaltenen neuen ternären Metallboride EuOs4B4 und EuIr4B4 kristallisieren in einer Struktur vom NdCo4B4‐Typ.

New ternary metal borides with compositionR. E. T4B4 (R. E.=rare earth metal,T=transition metal) have been synthesized within the systems [La,Ce,Pr,Nd,Sm]−Os−B and [Y, La, Ce, Pr, Nd, Sm, Gd, Tb]−Ir−B. All compounds were found to be crystallizing with NdCo4B4-type structure. Magnetic measurements (80–300 K,Curie-Weiss behaviour, θ p ~ 16K and µeff=9.94µB for TbIr4B4) indicate Y andR. E. elements (except Ce) to be trivalent in these compounds. The crystal chemistry of the isotypic series [Y,R. E.] [Os,Ir]4B4 is discussed.