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 (Cm):

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

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