Weiguo Sun

Our study reveals the electronic structures and features of isotropically contracted Y ₂ O ₃ :Eu ³⁺ and anisotropically compressed Y ₂ O ₃ :Pr ³⁺ under pressure.

Ambient-pressure stable doped C ₄₈ fullerene combines mechanical robustness with flat-band induced electronic features, highlighting its potential as a platform for novel superconducting carbon-based systems.

Rare-earth ion (Pr³⁺, Nd³⁺, and Tm³⁺)-doped yttrium vanadate (YVO₄) crystals have aroused great research interest owing to their excellent laser performances. However, the microstructures, which underlie the optical properties of these crystals, are still unclear. In this paper, the stable crystal structures of the YVO₄:Re (Re = Pr, Nd, and Tm) systems are predicted by using the crystal structure analysis by the particle swarm optimization (CALYPSO) structure search method. The unique tetragonal structures with the P4̅m2 (no. 115) space group for the YVO₄:Re crystals are identified for the first time. It is found that the rare-earth ions (Pr³⁺, Nd³⁺, and Tm³⁺) can accurately occupy the Y³⁺ sites and successfully fuse into the YVO₄ host crystals. The simulated X-ray diffraction (XRD) patterns of the YVO₄ and YVO₄:Re (Re = Pr, Nd, and Tm) are consistent with the experimental measurements, demonstrating the possibility and rationality of the predicted structures. Furthermore, we are motivated to clarify the electronic properties of the pure YVO₄ and YVO₄:Re (Re = Pr, Nd, and Tm) crystals based on density functional theory (DFT). The calculated electronic band structures of YVO₄:Re (Re = Pr, Nd, and Tm) indicate reductions in the band gaps. With the increase in f-electrons, the energies of the f-electrons in the conduction bands decrease slightly. The calculated electron localization functions (ELF) of YVO₄:Re (Re = Pr, Nd, and Tm) show that the bonding characteristics of Y-O, Pr-O, Nd-O, and Tm-O are all ionic. These theoretical results could provide important information for further research on the rare-earth-doped laser materials.

Transition metal borides have garnered significant research interest due to their versatile properties, including superconductivity and exceptional hardness. This study examines the stable crystal structures of Rhodium-Boron (Rh-B) compounds under high pressure using first-principles structural searching. Beyond the previously known Rh₂B, RhB₂, and RhB₄ phases, three new boron-rich phases—C2/m-RhB₆, Amm2-RhB₆, and Cmca-RhB₈—are identified, each characterized by three-dimensional covalent bonding networks. Their mechanical and thermodynamic stability is validated through elastic property assessments and phonon dispersion calculations. Surprisingly, these phases exhibit low bulk and shear moduli, ruling them out as candidates for hard materials. The metallic character of these borides is evident from their electronic density of states, which exhibits a sharp peak at the E_F-a signature often associated with superconducting systems. Indeed, our calculations predict T_c values of 8.93 K and 9.36 K for Amm2-RhB₆ and Cmca-RhB₈, respectively, at 100 GPa.

Rare earth (RE) borides have garnered significant attention due to their high mechanical strength, superconductivity, and novel electronic properties. In this study, we systematically investigate the structural, electronic, and mechanical properties of RE neodymium borides across a wide range of pressures. Various stoichiometries of Nd–B compounds are predicted using the unbiased CALYPSO structure search method and density functional theory calculations. Our findings indicate that the newly predicted NdB₅, NdB₇, and NdB₈ compounds are thermodynamically and mechanically stable at high pressures. Detailed analyses of the electronic band structure and density of states reveal that all neodymium borides exhibit metallic behaviour. The hardness of the stable phases has been evaluated using an empirical model. Notably, NdB₅ compound could also be dynamically and mechanically stable at ambient pressure with an estimated hardness of approximately 24.82 GPa, suggesting that NdB₅ is a potential hard metal boride. Our results provide valuable insights into the structural, electronic, and mechanical properties of Nd–B compounds, enhancing our understanding of their potential applications in various fields.

Of particular interest is the serendipity of distinctive nonmetallic layered frameworks with the stoichiometry of 1:2 in the binary metallic compounds within inorganic chemistry and materials science. This not only gives rise to the unexpected properties, especially the distinguished superconductivity, as reflected in MgB2, MoB2, NaC2, LaP2 and CeP2, but also strengthens the cognition of the elemental contributions. Although various investigations on the superconducting performances in the alkali, alkaline-earth and rare-earth metal disilicides containing the silicon layers have been reported, the pursuit of superconductors with silicon-planar framework in transition metal disilicides remain unknown up to now. In the present work, crystal structure searches and first-principles calculations were thoroughly conducted in RuSi2 within the pressure range of 0-300 GPa to uncover the novel structures, incredible silicon building block and the amazing properties. The ground orthorhombic Cmca-RuSi2 phase at ambient pressure is a semiconductor with the band gap of 0.485 eV, whose hardness can reach 31.7 GPa. Even more intriguingly, the high-pressure orthorhombic Cmcm-RuSi2 configuration with the fabulous graphene-like silicon-layer, which can be theoretically stabilized with the transformation pressure of 50.97 GPa, can be unexpectedly recovered to ambient pressure. Electron-phonon coupling calculations unravels that it possesses the metallic trait with an estimated Tc value of 1.43 K at 75 GPa, which increases to 10.07 K under ambient pressure. The enhanced Tc stems from the increased density of states at the Fermi level and associated with the coupled vibrations between Ru and the planar Si layer. Meanwhile, the hardness value for Cmcm-RuSi2 is 26.8 GPa under ambient pressure, which further results from the three-dimensional covalent Ru-Si and Si-Si building blocks. The coexistence of superconductivity and high hardness in the Cmcm-RuSi2 configuration under ambient pressure will pave the way for delving into more binary transition-metal silicides and correlated ternary silicides with the profound silicon layers.