金属硼化物结构与性能

Souma S, Komatsu H, Takahashi T, et al. Electronic Band Structure and Fermi Surface of CaB6 Studied by Angle-Resolved Photoemission Spectroscopy[J]. Physical review letters. 2003, 90(2): 27202.
prepared by: luokan
Contents
• Structure of some typical metal borides • Properties and application of some metal borides
– MgB2 – ZrB2 – CaB6 …
• Conclusion
ZrB2
The finite DOS at the Fermi level highlights the metallic behavior of both materials while the sharp valley is accounted for by the excellent thermal and chemical resistance of these ultrahigh temperature ceramics.
MgB2
• Its superconductivity was discovered by the group of Akimitsu in 2001. Its critical temperature (Tc) of 39 K is the highest amongst conventional superconductors. This material was first synthesized and its structure confirmed in 1953 but its superconducting properties were not discovered until 2001. • Two types of doping to improve the superconductivity of MgB2
ZrB2
Passerone A, Muolo M L, Novakovic R, et al. Liquid metal/ceramic interactions in the (Cu, Ag, Au)/ZrB2 systems[J]. Journal of the European Ceramic Society. 2007, 27(10): 3277-3285.
Boron polymorphs
β-rhombohedral boron
Density(g/cm3)
α-boron β-boron 2.46 2.35 Vickers Hardness(GPa) 42 45 Bulk Modulus(GPa) 185 224
Bandgap(eV)
2 1.6
Liu G, Niu P, Yin L, et al. α-Sulfur Crystals as a Visible-Light-Active Photocatalyst[J]. Journal of the American Chemical Society. 2012, 134(22): 9070-9073.
– (Vajpayee A, Awana V P S, Balamurugan S, et al. Effect of PVA doping on flux pinning in bulk MgB2[J]. Physica C: Superconductivity. 2007, 466(1–2): 46-50.)
EuB6 nanowires
Xu J, Chen X, Zhao Y, et al. Self-catalyst growth of EuB6 nanowires and nanotubes[J]. Journal of Crystal Growth. 2007, 303(2): 466-471.
Metal Borides
• Boron is a chemical element with symbol B and atomic number 5 • Boron (B) naturally occurs in two isotopes, 10B and 11B, the latter of which makes up about 80% of natural boron • Boron can form a metal boride with almost all metals at high temperatures • Metal Borides(MmBn) tend to form interstitial compouds,
MB6 nanostructures
Scheme of a metal-catalyzed CVD process for the synthesis of MB6 nanostructures.
MB6 nanostructures
Scheme of a self-catalyzed CVD process for the synthesis of MB6 nanostructures
MgB2
The temperature dependences of the normalized resistivity ρ(T)/ρ(300 K)for the samples of MgB2, Mg0.98Ca0.02B2 and Mg0.92Ca0.08B2.
Sun Y, Yu D, Liu Z, et al. Structural and superconducting properties of Ca-doped MgB2 superconductors[J]. Superconductor Science and Technology. 2007, 20(3): 261.
Metal Borides
Metal Borides
Metal Borides
One single cell of YB66
Metal Borides
来自百度文库 MgB2
Magnesium diboride (MgB2) is a simple ionic binary compound that has proven to be an inexpensive and useful superconducting material. Density 2.57 g/cm3 Melting point 830℃
PrB6 nanowires
CaB6 nanowires
Xu J, Zhao Y, Zou C, et al. Self-catalyst growth of single-crystalline CaB6 nanostructures[J]. Journal of Solid State Chemistry. 2007, 180(9): 2577-2580.
• 20% Cu doping MgB2 raise Tc to 49K, and Tc0 = 45.6 K
– (Sun Y P, Song W H, Wen H H, et al. Superconductivity at 49 K in copper doping magnesium diboride[Z]. 2001.)
Metal Borides: Structure and Performance
Carenco S, Portehault D, Boissiè re C, et al. Nanoscaled Metal Borides and Phosphides: Recent Developments and Perspectives[J]. Chemical Reviews. 2013, 113(10): 7981-8065.
Density 2.45 g/cm3 Melting point 2235℃ Crystal structure Cubic Microhardness 27GPa
CaB6
Experimental band structure of CaB6 along the ΓX direction determined by ARPES. Bright areas correspond to bands. LDA and LDA＋GW band calculations are also shown by white and red lines, respectively, for comparison.
ZrB2
• Zirconium diboride (ZrB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure • ZrB2 is an ultra high temperature ceramic (UHTC) with a melting point of 3246 ℃ • A candidate material for high temperature aerospace applications such as hypersonic flight or rocket propulsion systems • High thermal and electrical conductivities, similar with isostructural titanium diboride(TiB2) and hafnium diboride(HfB2)
ZrB2
Diffusion barriers
ZrB2
• Lattice parameters and thermal expansion coefficients are close to AlN and GaN for instance • Crystalline ZrB2(0001) can be epitaxially grown on Si(111) by single source CVD above 900℃, could be a good buffer layer for “nitride over silicon” technologies • the as-grown 20−30 nm thick crystalline films are metallic with electrical conductivity close to bulk values and high reflectance in the visible to UV range,
– Mg1-xMxB2(Al, Be, Ca, Cu, Li, Na, Zn…) – MgB2-yXy(Be, C, N, O…)
MgB2
• Various means of doping MgB2 with carbon can improve the upper critical field and the maximum current density, 5% doping with carbon can raise Hc2 from 16 T to 36 T whilst lowering Tc only from 39 K to 34 K
CaB6
• • • • • • • Antioxidant Deoxidation agent High temperature material Wear resistant material Hot cathode material Neutron absorber A promising n-type thermoelectric materials