Structural and Physical Properties Diversity of New CaCu5-Type Related Europium Platinum Borides
Three novel europium platinum borides have been synthesized by arc melting of constituent elements and subsequent annealing. They were characterized by X-ray powder and single-crystal diffraction: EuPt4B, CeCo4B type, P6/mmm, a = 0.56167(2) nm, c = 0.74399(3) nm; Eu3Pt7B2, Ca3Al7Cu2 type as an ordered variant of PuNi3, R3̅m, a = 0.55477(2) nm, c = 2.2896(1) nm; and Eu5Pt18B6–x, a new unique structure type, Fmmm, a = 0.55813(3) nm, b = 0.95476(5) nm, c = 3.51578(2) nm. These compounds belong to the CaCu5 family of structures, revealing a stacking sequence of CaCu5-type slabs with different structural units: CaCu5 and CeCo3B2 type in EuPt4B; CeCo3B2 and Laves MgCu2 type in Eu3Pt7B2; and CaCu5-, CeCo3B2-, and site-exchange ThCr2Si2-type slabs in Eu5Pt18B6–x. The striking motif in the Eu5Pt18B6–x structure is the boron-centered Pt tetrahedron [BPt4], which build chains running along the a axis and plays a decisive role in the structure arrangement by linking the terminal fragments of repeating blocks of fused Eu polyhedra. Physical properties of two compounds, EuPt4B and Eu3Pt7B2, were studied. Both compounds were found to order magnetically at 36 and 57 K, respectively. For EuPt4B a mixed-valence state of the Eu atom was confirmed via magnetic and specific heat measurements. Moreover, the Sommerfeld value of the specific heat of Eu3Pt7B2 was found to be extraordinarily large, on the order of 0.2 J/mol K2.
ÜberSE-Metall—Kobaltboride
YbCo3B2, PrCo2B2 and HoCo2B2 have been prepared from the components. YbCo3B2 belongs to the ordered CaCu5-type structure, PrCo2B2 and HoCo2B2 crystallize with the ordered BaAl4-(ThCr2Si2)-type structure. The crystal chemistry of the isotypic series ofRECo3B2 as well as ofRECo2B2 compounds will be discussed.
Raumchemie der festen Stoffe
PROF. BILTZ is well known for his long series of researches on the physical chemistry of solids. In this book, which brings together much previously published material and also many determinations which have not otherwise been published, he attempts a systematic survey of the whole field, the primary object being the determination of the absolute volumes of the ions in crystals. The first part of the book consists of a number of detailed tables, in which the rich experimental material is collected in an easily appreciated form, and in the second part a detailed discussion of this quantitative material is presented.Raumchemie der festen Stoffe.Von Wilhelm Biltz. Pp. x + 338. (Leipzig: Leopold Voss, 1934.) 22.50 gold marks.