SUPERCONDUCTIVITY IN A TRANSITION METAL BORIDE
Discovery of superconductivity at 39K in MgB2
Jun Akimitsu of Aoyama-Gakuin University
in Tokyo and co-workers announced their discovery at the
Symposium on Transition Metal Oxides held in
Sendai in 10 January 2001.
TRANSITION METAL BORIDES
XB2
X= Mg, Al, Ag, Cr, Hf, Mo, Nb, Os, Pd, Ru, Sc, Ta, Ti, U, V, Zr
STRUCTURE
The compounds XB2 are exagonal, with a unimolecular cell. The structure is formally related to that of Cd(Oh)2, with atoms in the same special positions of
D3d3 (C
m):
X:
(1a)
000
B:
(2d)
1/2 2/3 u; 2/3 1/3
(Table of Space Group Symbols)
In XB2, however is ca. 1/2 instead of 1/4. This different parameter results in a grouping of alternate layers of aluminum and boron atoms normal to the C0 axis, each aluminum having 12 equidistant boron neighbors at 2.37 Å, six in the plane above and six in the plane below (Fig. below). In the boron planes each atom is surrounded by an equilateral triangle of atoms, with B-B = 1.73 Å.
The compound aluminum boride, AlB2, having the edges: a0 = 3.009 Å, c0 = 3.262 Å. Other borides and several intermetallic compounds with this atomic arrangement are given in the table below:
Superconductivity at 39 K in MgB2 (to be published)
J. Nagamatsu, N.Nakagawa,T.Muranaka,Y.Zenitani and J.Akimitsu
The structure of AlB2
Hoffmann and Jänicke
Naturwiss. 23, 851 (1935)
The structure of AlB2
Hoffmann and Jänicke
Z. Physik. Chem. 31 B, 214 (1936)
Neutron Diffraction Study of MnB2
E. Legrand and S. Neov
Solid State Communications 10, 883 (1972)
ELECTRONIC STRUCTURE
Band Structure and Density of States of Light-Metal Diborides
I.I. Tupitsyn
Sov. Phys Solid State 18, 1688 (1976)
SYNTHESIS
Synthesis of Transition Metal Borides and their Properties
E.A. Knyshev, V.M. Novgorodtsev, U.S. Plyshevski, V.A. Kobyakov, Z.G. Stepanova, V.V. Svistunov and A.R. Becketov
J. of the Less-Common Metals 47, 273 (1976)
The Preparation of AlB2
Felten
J. Am. Chem. Soc. 78, 5977
The crystallization and growth of AlB2 single crystal flakes in aluminum
C. Deppisch, G. Liu, A. Hall, Y. Xu, A. Zangvil, J.K. Shang and J. Economy
Journal of Materials Research 13, 3485 (1998)
Low-temperature sintering and elongated grain growth of 6H!=SiC powder with AlB2 and C additives
H. Tanaka and Y. Zhou
Journal of Materials Research 14, 518 (1999)
Structural Phase Transition of HoGa2 at High Pressure
Schwarz U, Brauninger S, Grin Y, Syassen K and Hanfland M
Journal of Alloys & Compounds. 268, 161(1998)
Combustion Synthesis of TiB2/Al Composites as a Grain Refiner of Aluminum Alloys
Experimental Analysis of the Intermediary Phases AlB2, AlB12
TiB2 in the Al-B and Minerals and Other Solids: Sulfides, Silicides, etc.
To buy MgB2 samples