The electronic structure and chemical stability of the AlB₂-type transition-metal diborides

Abstract

The electronic structures of the AlB2-type transition-metal diborides TMB2 (TM=Sc,Ti,V,Cr,Mn,Y,Zr,Nb,Mo,Hf,Ta) have been calculated by using the self-consistent LMTO-ASA method. The binding mechanism is discussed and the rigid-band model is shown to provide a fairly good description of their electronic structures. The existence of a pseudogap in the total density of states is found to be a common feature of these compounds. The variation of the chemical stabilities of these diborides is analysed and we find that the trends can be understood in terms of the band-filling concept of the bonding states. The results are compared with other theoretical and experimental work.

Effect of pressure on the magnetic properties of CrB2

“…4, and it is in a qualitative agreement with the results of KKR-ASA [7] and LMTO-ASA [8][9][10] In order to evaluate the bulk modulus value to be used in the analysis of the pressure effects in CrB 2 , the band structure calculations were performed for a number of lattice parameters close to the experimental ones (the ratio c/a was fixed at its experimental value 1.033). The equilibrium unit cell volume V th and the corresponding theoretical bulk modulus B LDA were determined from the calculated volume dependence of the total energy E V ( ) by using the well known Murnaghan equation [14], and appear to be V th = 21.79 C 3 and B LDA = 3.23 Mbar.…”

“…The electronic spin susceptibility of CrB 2 is also an order of magnitude higher than that of other diborides, demonstrating a large exchange-enhancement effect. The band structure calculations for CrB 2 [7][8][9][10] have shown that its Fermi level lies in a region of the high density of electronic states (DOS). Therefore the Stoner criterion is nearly fulfilled in CrB 2 , and the susceptibility enhancement factor, S ; 9, was estimated [7,9].…”

Debye Temperatures of Transition Metal Diborides TMB2 (TM= Ti, Zr, Os, Nb, Ru) Under Pressure

“…However, the fact that the B-B bond length in the diborides ranges from 1.7 to 1.8A˚, values typical of B-B single bonds, immediately suggests that there is an insignificant degree of p bonding between the B atoms. This conclusion is supported by recent electronic structure calculations and other data indicating that the metal-boron bonding is largely covalent in nature [8][9]. Although the structures of the diborides are unique, their physical properties are somewhat similar to those of nitrides and carbides; they are extremely hard and have very high melting points [10].…”

NMR study of B‐2p Fermi‐level density of states in the transition metal diborides

“…In addition, the F ( ) p N E values in the fourth group (TiB 2 , ZrB 2 , and HfB 2 ) are consistently smaller than those in the fifth group (VB 2 , NbB 2 , and TaB 2 ). This observation agrees with the picture within a rigid-band scenario: F E falls at the DOS minimum for TM = Ti, Zr, Hf, and shifts to Table. compound higher DOS with increasing d-electron counts [22,23,31]. Therefore, the present NMR investigation gives an experimental understanding for the electronic band characteristics of these diborides.…”