Comparative NMR investigation of the Re-based borides

Abstract

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.

Phase stability and mechanical properties of rhenium borides by first‐principles calculations

“…This indicates that they are thermodynamically stable and might be synthesized at ambient conditions. Among these structures, it is noted that Re 3 B, Re 7 B 3 , and ReB 2 were synthesized experimentally1, 2 and their properties were studied extensively by experiments 3–6, 8–12. On the other hand, the formation enthalpy of the experimentally observed ReB 3 is positive (2.92eV, in agreement with previous theoretical value of 3.08eV23), indicating that it is thermodynamically unstable at ambient conditions.…”

“…and 3.1–3.3 K,4, 5 respectively. For ReB 2 , early study indicates that it is a superconductor with transition temperature of 4.5–6.3 K depending on the boron compositions,3 while the later one shows that it exhibits no superconducting signature 5. Recently, there is a renewed interest on ReB 2 due to its superior mechanical properties.…”

“…194). The recent studies on the physical properties of Re 3 B and Re 7 B 3 indicate that they are superconductors with the transition temperatures 4.6–4.8 (Refs 3–54, 5 respectively.…”

“…The recent studies on the physical properties of Re 3 B and Re 7 B 3 indicate that they are superconductors with the transition temperatures 4.6–4.8 (Refs 3–54, 5 respectively. For ReB 2 , early study indicates that it is a superconductor with transition temperature of 4.5–6.3 K depending on the boron compositions,3 while the later one shows that it exhibits no superconducting signature 5.…”

Prediction of new high pressure phase of TaB3: First-principles

“…Where E B is calculated based on the structure of α-B 12 boron at low pressure [33]. The implication of this definition is that if the ΔH is negative, the considered compound is thermodynamically stable; while it is positive, the compound is thermodynamically unstable [34]. The calculated bulk modulus B and shear modulus G were from the Voigt-Reuss-Hill approximations [35][36][37].…”