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.
Die ternären Calcium-Nickelboride CaNi4B, Ca3Ni7B2, Ca5Ni15B4 und CaNi15B6
The crystal structures of four calcium nickelborides were determined by means of Single crystal X-ray methods. CaNi^B [hexagonal, P6/ mmm, a = 5.066(1) Ä, c = 6.844(1) Ä, Z = 2] crystallizes with the CeCo4B type of structure [R = 0.054, 265 refl., 14 variables). CajNiyBj [trigonal, Rhm, a = 5.157(2) Ä, c = 21.433(7) Ä, Z = 3] is isotypic with CajAIvCuz {R = 0.036, 603 refl., 15 variables). Ca5Nii5B4 [hexagonal, PSilmmc, a = 5.115(2) Ä, c = 27.946(4) Ä, Z = 2] forms a new structure by block stacking of MgZnz-, CaCusand CeCojBz-type slabs (R = 0.073,615 refl., 34 variables). CaNiizBe [trigonal, Ä3m, a = 9.528(1) Ä, c = 7.407(1) Ä, Z = 3] is isotypic with SrNiizBg (R = 0.038, 414 refl., 21 variables).
Magnetic properties of the new NpGe2−x (ThSi2 type) binary compound
Abstract We have performed magnetic investigation of the new neptunium–germanium binary phase NpGe2−x (x=0.28) which crystallises with the defect tetragonal ThSi2 type of structure. The magnetisation measurements reveal the onset of ferromagnetic interactions below TC=121 K. The 237Np Mossbauer spectroscopy investigation indicates the occurrence of Np3+ ions carrying an average ordered moment of 2.17 μB.