Theoretical study of electronic structure and superconductivity in Nb1−xB2 alloys

Mechanical and electronic properties of diborides of transition 3d–5d metals from first principles: Toward search of novel ultra-incompressible and superhard materials

“…Next, investigation of non-stoichiometric effects on the properties of borides, in particular, the influence of metal deficiency, seems to be fundamentally important. This effect (metal deficiency) was established [255][256][257][258][259] and simulated [65,[260][261][262][263][264] for a series of diborides of s, p, and d metals: Nb 1Àx B 2 , Ta 1Àx B 2 , Al 1Àx B 2 , Mg 1Àx B 2 , etc., review [66]. Other interesting directions involve ab initio simulations of elastic properties of metal diborides under pressure [242,265], as well as numerical calculations of lattice dynamical properties (phonon spectra) and the temperature-dependent behavior of thermodynamical properties such as entropy, heat capacity, internal energy, and free energy of these materials [266].…”

Structural phase evolution and superconductivity in the non-stoichiometric intermetallic compound niobium diboride

“…Nevertheless some controversies still exist due to the lack of experimental results about the detailed electronic structure of non-stoichiometric Nb 1Àx B 2 samples, especially from single crystals [11][12][13][14][15]. Recently Farrell et al [16] suggested that the formation of substitutional boron dimers at Nb site rather than niobium vacancies would cause the raise of T c , and their calculations indicated a higher DOS at E F upon the formation of boron dimers than niobium vacancies.…”

NMR and Seebeck coefficient studies of the electronic band structure in Nb1−xB2

“…Remarkably, such a feature is in good agreement with the prediction from band structure calculations based on the existence of the Nb vacancies in the Nbdeficient Nb 1−x B 2 samples. 22,26 Those calculations indicated a notable pseudogap, about 1 eV below E F , which locates at the antibonding states for NbB 2 . By removing Nb from stoichiometry, E F will shift toward the low energy side accompanied by the decrease in N͑E F ͒.…”

“…Theoretical calculations indicated that the electronic Fermi level ͑E F ͒ DOS, N͑E F ͒, is reduced by introducing Nb vacancies in Nb 1−x B 2 . [21][22][23] On the other hand, Farrell et al 24 proposed that the formation of the substitutional B dimers at the Nb sites instead of the Nb vacancies would cause an increase in N͑E F ͒. Hence, the atomic picture of the Nb-deficient compositions Nb 1−x B 2 remains debatable.…”