Structural, mechanical, and electronic properties of Rh2B and RhB2: first-principles calculations

A new pressure-densified orthogonal hard superconducting phase of RhB4

A new hard superconducting phase of RhB4 with the space group Cmca is predicted, and the phase transition and mechanical and superconducting properties of RhB4 under 300 GPa are studied using first principles. We predict a new high-pressure phase of RhB4 by substituting the most stable Cmca structure of OsB4, known for its excellent mechanical properties. The calculated enthalpy shows that above 112.6 GPa, Cmca is superior to Pmmn as was previously predicted by particle swarm optimization. The stability of the predicted phase is checked using formation enthalpy, elastic constant and phonon dispersion. Additionally, the convex hull of the Rh-B system confirms that the phase is expected to be synthesized experimentally. The Cmca phase is an incompressible hard material with a hardness of 23.75 GPa at 300 GPa attributed to strong intralayer covalent B-B bonds. Furthermore, the phase is a relatively pressure-insensitive superconductor, with a Tc of 8.6 K at 112.6 GPa and a pressure-dependent coefficient of -0.03 K GPa-1. The finding reveals a superconducting hard material that is well-suited for extreme high-pressure environments.

A first-principles study on the phase stability and physical properties of a B-site ordered Nd2CrFeO6 double perovskite

Here, the first-principles predictions on the structural stability, magnetic behavior and electronic structure of B-site ordered double perovskite Nd₂CrFeO₆ have been reported. Initially, the ground state of the parent single perovskites NdCrO₃ and NdFeO₃ has been studied to determine the relevant Hubbard U parameter to investigate the properties of Nd₂CrFeO₆. The thermodynamic, mechanical, and dynamic stability analyses suggest the possibility of the synthesis of the Nd₂CrFeO₆ double perovskite at ambient pressure. The compound shows a ferrimagnetic nature with 2 μ_B net magnetic moment and the magnetic ordering temperature has been estimated to be ∼265 K. The electronic structure indicates a higher probability of direct photon transition over the indirect transition with a band gap of ∼1.85 eV. Additional effects of Nd (4f) spin and spin-orbit coupling on the band edges have been found to be negligible for this 4f-3d-3d spin system. This first-principles investigation predicts that due to the ferrimagnetic nature and a significantly lower band gap compared to those of its antiferromagnetic parent single perovskites, the B-site ordered Nd₂CrFeO₆ double perovskite could be a promising material for spintronic and visible-light driven energy applications.

A first-principles investigation of a new hard multi-layered MnB2 structure

A novel high-pressure phase of multi-layers Immm-MnB₂ is confirmed on the convex hull diagram of the Mn-B systems at 50 GPa (b).

Unexpected superhard phases of niobium triborides: first-principles calculations

Using an unbiased structure search method based on particle-swarm optimization algorithms in combination with density functional theory calculations, we investigate the phase stability and electronic properties of NbB₃ under high pressures.