12230-32-9Relevant articles and documents
A reactivity study in the Mg-B system reaching for an improved synthesis of pure MgB2
Schmitt, Ruth,Glaser, Jochen,Wenzel, Thomas,Nickel, Klaus G.,Meyer, H.-Jürgen
, p. 38 - 42 (2006)
The binary Mg-B system was studied with respect to the existing phases MgB2, MgB4, MgB7, and MgB12 and their transformations into each other. As a result of these studies, a new synthesis route is reported for MgB2 by reacting MgB4 and Mg with each other. The obtained MgB2 was characterized by Rietveld refinement of the powder XRD pattern (RBragg = 3.56%, Rwp = 10.6%), magnetic measurements, and by electron probe microanalysis (EPMA). With this new synthesis route, a better phase homogeneity is obtained when compared with MgB2 samples prepared from the elements.
Synthesis, Crystal Structure, and Properties of MgxB 50C8 or Mgx(B12)4(CBC) 2(C2)2 (x = 2.4-4)
Adasch, Volker,Schroeder, Melanie,Kotzott, Dominik,Ludwig, Thilo,Vojteer, Natascha,Hillebrecht, Harald
, p. 13723 - 13732 (2010)
Single crystals of a new magnesium boride carbide MgxB 50C8 (x = 2.4-4) were synthesized from the elements in a metallic melt using tantalum ampules. Crystals were characterized by single crystal X-ray diffraction and electron microprobe analysis. The variation of the Mg content results from different reaction conditions. The composition Mg ～3B50C8 is by far the most favored. It fulfills the electron counting rules of Wade and Longuet-Higgins and thus explains the light-green to yellow transparent color. The structure of Mg ～3B50C8 (C2/m, Z = 1, a = 8.9384(12) A, b = 5.6514(9) A, c = 9.6021(13) A, β = 105.86(1)°) consists of B12 icosahedra. The icosahedra are interconnected by four exohedral B-B bonds to layers. The layers are connected to a three-dimensional covalent network by C2 and CBC units and further exohedral B-B bonds. The Mg sites are partially occupied. Different site occupation factors cause the various compositions and colors (Mg 2.4B50C8, brown; Mg4B 50C8, black). The vibrational spectra show the modes of B12 icosahedra and C2 and CBC units as well. Measurements of the microhardness according to Vickers and Knoop revealed remarkably high values of HV = 3286 (32.0 GPa) and HK = 3165 (31.5 GPa), which exceed the values of B4C. Optical spectra reveal a band gap of 2.7 eV for Mg～3B50C8, in agreement to the observed color. This justifies an ionic description, and the formula can be written as (Mg2+)3(B122-) 4(CBC+)2(C2)2.
Synthesis and crystal structure of MgB12
Adasch, Volker,Hess, Kai-Uwe,Ludwig, Thilo,Vojteer, Natascha,Hillebrecht, Harald
, p. 2916 - 2926 (2006)
Single crystals of MgB12 were synthesized from the elements in a Mg/Cu melt at 1600 °C. MgB12 crystallizes orthorhombic in space group Pnma with a = 16.632 (3) A, b = 17.803 (4) A and c = 10.396 (2) A. The crystal structure (Z = 30, 5796 reflections, 510 variables, R1 (F) = 0.049, w R2 (I) = 0.134) consists of a three dimensional net of B12 icosahedra and B21 units in a ratio 2:1. The B21 units are observed for the first time in a solid compound. Mg is on positions with partial occupation. The summation reveals the composition MgB12.35 or Mg0.97B12, respectively. This is in good agreement with the value of MgB11.25 as expected by electronic reasons to stabilize the boron polyhedra B122 - and B214 -.
