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

Lue, Chin Shan; Lai, W. J.

doi:10.1002/pssb.200402136

Cited by 17 publications

(21 citation statements)

References 28 publications

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“…3, the Knight shifts of these borides are temperature independent, a typical response for ordinary metals. For ReB 2 , an extremely small Knight shift of about 10 ppm was found, similar to other transition metal borides 15 as well as MgB 2 ͑Refs. 13, 16, and 17͒.…”

Section: Resultssupporting

confidence: 78%

“…H hf orb represents the orbital hyperfine field per unit orbital angular momentum and can be evaluated using H hf orb =2 B ͗r −3 ͘ p , where ͗r −3 ͘ p is the average over the occupied p orbitals. Taking an estimated value of 1.65a B for the boron radius of p electrons in ReB 2 , 15 it yields ͗r −3 ͘ p = 1.35ϫ 10 25 cm −3 , corresponding to H hf orb = 2.5ϫ 10 5 G. With the above relationship and experimental NMR T 1 T, we can thus extract N p ͑E F ͒ = 0.24 states/ eV f.u.. This result is in good agreement with 0.2-0.3 states/eV obtained from band-structure calculations, 10,11 suggesting a reliable estimate for the present analysis.…”

Section: Resultsmentioning

confidence: 99%

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Comparative NMR investigation of the Re-based borides

Lue

Tao

2008

Phys. Rev. B

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We report a systematic study of the rhenium-based borides, ReB 2 , Re 7 B 3 , and Re 3 B, by means of the 11 B nuclear magnetic resonance ͑NMR͒ spectroscopy. While Re 7 B 3 and Re 3 B are superconductors, ReB 2 exhibits no superconducting signature but is of current interest due to its superhard mechanical property. Since the major focus of this investigation is their electronic characteristics in the normal states, we performed the measurements at temperatures between 77 and 295 K. For Re 7 B 3 and Re 3 B, s-character electrons were found to be responsible for the observed 11 B NMR Knight shift and spin-lattice relaxation rate ͑1 / T 1 ͒. From T 1 analysis, we thus deduce the partial B s Fermi-level density of states ͑DOS͒ of both borides. On the other hand, the relaxation rate of ReB 2 is mainly associated with p electrons, similar to the cases of OsB 2 and RuB 2 . In addition, the extracted B 2p Fermi-level DOS is in good agreement with the theoretical prediction from band-structure calculations.

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Section: Resultssupporting

confidence: 78%

Section: Resultsmentioning

confidence: 99%

Comparative NMR investigation of the Re-based borides

Lue

Tao

2008

Phys. Rev. B

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“…In fact, in other diborides, for example TaB 2 or NbB 2 , the Fermi level is shifted out of this valley, resulting in a deterioration of properties . These results are consistent with X‐ray photoelectron spectra and NMR results …”

Section: Electronic Structuresupporting

confidence: 87%

Ab Initio Computations of Electronic, Mechanical, and Thermal Properties of ZrB₂ and HfB₂

Lawson

Bauschlicher

Daw

2011

Journal of the American Ceramic Society

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A comprehensive ab initio analysis of the ultra high temperature ceramics ZrB 2 and HfB 2 is presented. Density functional theory (DFT) computations were performed for the electronic, mechanical, thermal, and point defect properties of these materials. Lattice constants and elastic constants were determined. Computations of the electronic density of states, band structure, electron localization function, etc. show the diverse bonding types that exist in these materials. They also suggest the connection between the electronic structure and the superior mechanical properties. Lattice dynamical effects were considered, including phonon dispersions, vibrational densities of states, and specific heat curves. Point defect (vacancies and antisites) structures and energetics are also presented. W.-Y. Ching-contributing editor Manuscript No. 29044.

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“…Transition metal based diborides, isostructural to the AlB 2 -type structure ͑space group P6 / mmm͒, have thus refocused interest. [2][3][4][5][6][7][8] Among these diborides, some systems have been observed to exhibit superconducting behavior with very low transition temperature ͑T c ͒, while a substantial T c enhancement has been achieved as deviating from ideal stoichiometry. The titled compound NbB 2 is a material of this prototype.…”

Section: Introductionmentioning

confidence: 99%

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

Lue

Kuo

2008

Journal of Applied Physics

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With the aim of providing experimental information for the Nb deficiency enhanced superconducting temperature (TC) in the Nb1−xB2 samples, we carried out a study on Nb1−xB2 (x=0, 0.13, 0.20, and 0.26) by means of nuclear magnetic resonance (NMR) and Seebeck coefficient (S) measurements. From the N93b NMR spin-lattice relaxation rates, we can deduce the Nb 4d partial Fermi level density of states (DOS) Nd(EF) for each individual composition. The result indicates that Nb0.74B2 and Nb0.80B2 possess large Nd(EF) while the lowest one appears in Nb0.87B2. The Seebeck coefficient also shows smaller absolute values in Nb0.74B2 and Nb0.80B2, associated with higher Fermi level DOS in both compounds. Interestingly, the temperature variation in S exhibits a broad minimum in Nb0.87B2, which is attributed to the presence of a pseudogap near the Fermi level. These observations were found to be in good agreement with the prediction from band structure calculations based on the appearance of the Nb vacancies in Nb1−xB2. In addition, the present study clearly reveals that the observed Tc enhancement by Nb deficiency has no direct relevance to their electronic Fermi level DOS.

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

Cited by 17 publications

References 28 publications

Comparative NMR investigation of the Re-based borides

Comparative NMR investigation of the Re-based borides

Ab Initio Computations of Electronic, Mechanical, and Thermal Properties of ZrB₂ and HfB₂

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

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

Cited by 17 publications

References 28 publications

Comparative NMR investigation of the Re-based borides

Comparative NMR investigation of the Re-based borides

Ab Initio Computations of Electronic, Mechanical, and Thermal Properties of ZrB2 and HfB2

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

Contact Info

Product

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Ab Initio Computations of Electronic, Mechanical, and Thermal Properties of ZrB₂ and HfB₂