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MgB 2 has a wide range of applications as a crucial superconducting material in fields such as electronics and communications, but its weak mechanical properties limit its use in extreme environments such as high pressure. Therefore, this article explores the enhancement mechanism of the mechanical properties for MgB 2 by substituting Mg sites with Nb element based on first principles. After substitution, NbB 2 has better thermodynamic stability, and the introduction of Nb-d state enhances light absorption. In terms of mechanics, due to the higher electron accumulation density in the Nb–B bond and a shorter bond length (2.451 Å), the atomic interactions become tighter and stronger. As a result, both elastic constants and modulus are enhanced, exhibiting high stiffness, high compression resistance, etc. The spatial distribution of 3D elastic anisotropy is closer to a spherical shape and the universal anisotropy index (A U ) tends to approach 0, which indicates the mechanical properties in all directions are more consistent, making it easier to predict and control. Meanwhile, the elastic modulus rises smoothly with increasing hydrostatic pressure and is not affected by lattice compression at low hydrostatic pressure. The change rate of B–B bond length is 6.8 % at 100 GPa, which becomes the main reason for the enhancement of mechanical properties. The article provides a theoretical foundation for the preparation of superconductors with excellent mechanical properties under extreme conditions. [ABSTRACT FROM AUTHOR]

Anatase TiO 2 is widely used in solar photocatalysis. However, the optical properties are limited by its ability to capture visible light and its poor activity. In order to obtain ideal material properties, GGA + U method based on density functional theory is used to study the electronic structure and optical properties of anatase phase TiO 2 and its (112) surface and Cr and Co-doped TiO 2 (112) surface. The results show that the transition metal Cr-doped system is more stable than the Co-doped system. The four systems exhibit semiconducting properties. The indirect band gap value of intrinsic TiO 2 is 3.245 eV, and the impurity bands appear in the spin-up energy bands after Cr, Co doping. The impurity states of the doped system spin split, which transforms the non-magnetic semiconductor into a semiconductor with net magnetic moments of 2 μB and 3 μB, respectively. In addition, the Cr, Co-doped systems show excellent optical properties, and the absorption coefficients are red-shifted in the range of (0–3 eV) with higher optical absorptivities. Through the investigation, it is evident that doping results in different degree of band gap change. As the conduction band moves towards the lower energy level, an impurity band is generated near the Fermi level. The presence of the impurity band fundamentally alters the initial transition mode of the electron, making the transition require less energy, thus enabling enhanced optical properties. The doping system enhances the lepton threshold of electrons and light absorption by changing the mode of inter-band leaps and decreasing the reflectivity, making them candidates in the field of optoelectronics and photocatalysis. [ABSTRACT FROM AUTHOR]

The layered structure of GeS exhibits commendable thermal stability and holds significant promise in the realms of optoelectronics and ion batteries. But its application is limited as dilute magnetic semiconductor. Therefore, this study delves into the impact of 3d transition metal (TM = V, Cr, and Mn) doping on the magnetic and optical characteristics of two-dimensional GeS monolayer through a first-principles calculation method grounded in density functional theory. The findings elucidate that all doping systems lead to a reduction in the band gap, with the V-doped system exhibiting the most significant diminishment. After doping process, magnetic coupling emerges between the electrons in the TM-3d state and those in the S-3p state, resulting in the manifestation of magnetic semiconductor characterized by magnetic moments of 3 μ B , 4 μ B , and 5 μ B , respectively. Comparative analysis with the pristine GeS monolayer, it reveals enhancements in optical absorptivity and refractive index within both the infrared and visible spectra of the doped systems. Notably, the V-doped system showcases superior optical properties due to its narrower band gap, facilitating more efficient electron transitions to the conduction band. Consequently, TM (TM = V, Cr, and Mn)-doped GeS monolayer hold promising potential in the realms of spintronics and optoelectronics. [ABSTRACT FROM AUTHOR]

The nanoindentation response of graphene (Gr) coating on nanotwin titanium-aluminum (nt-TiAl) matrix composites was studied using molecular dynamics (MD) simulation. The indentation velocity, twin boundary spacing, and parallel and vertical Z-axes are studied. The results show that the bearing capacity and hardness of Gr coating is significantly higher than that after coating failure, and the load-displacement curve shows the same phenomenon. Damage to the substrate material at varying speeds is indicated by atomic aggregation near the Gr coating, with the center of aggregation showing a negative correlation with indentation velocity. The matrix's damaged area is larger when the twin layer is perpendicular to the Z-axis and deeper when parallel, showing that the twin structure limits material damage by hindering dislocation expansion. Moreover, the presence of Gr coating delayed the matrix's plastic deformation process. This delay effect significantly improves the mechanical properties of composites, which have potential applications in aerospace. [ABSTRACT FROM AUTHOR]

The study of two-dimensional flexible materials in mechanic and optics has gained significant attention. By applying strain to modify the internal structure of materials, researchers can investigate the resulting mechanical and optical changes, offering exciting opportunities for further exploration in this field. The electronic structure, mechanical properties, and optical properties of the two-dimensional trigonal system Bi 2 Te 2 Se under biaxial strain regulation were investigated by using the first-principles plane pseudopotential plane wave method based on density generalized function theory. The analysis reveals that the energy bandwidth of Bi 2 Te 2 Se decreases with increasing strain until the band gap reaches 0 at 9% strain, causing the system to shift from a semiconductor to a conductor. The electronic density of states is primarily determined by the 6 p orbitals of Bi and 5 p orbitals of Te. With regards to its mechanical properties, Bi 2 Te 2 Se satisfies the mechanical stability criterion under different strains. As the strain increases from 0% to 6%, the material becomes increasingly brittle, with its interior transitioning from metallic to covalent bonds. However, the material toughness begins to improve from 6% to 9%, with the interior transitioning from covalent to metallic bonding. The performance improvement of Bi 2 Te 2 Se varies depending on the two electric field polarization vectors along [1 0 0] and [0 0 1] directions under strain. The material shows distinct application prospects in terms of absorption coefficient, reflectivity, refractive index, and lossiness under two directions. This paper provides a theoretical reference for the future mechanical and optical applications of Bi 2 Te 2 Se. [ABSTRACT FROM AUTHOR]