Narrow Results

In this paper, the electronic, optical, elastic, mechanical, and vibrational properties of glass B₂O₃ have been investigated. Simulations have been carried out including the P3₁21 structure. Our nonlocal empirical hybrid has accurately described the electronic band structure and band gap energy $E_g$ of the material. Our optical absorption plot has correctly identified the type of the glass B₂O₃ structure. The absorption plot also shows the interband indirect transitions from the valance O 2p¹ to conduction B 2p⁴ orbitals. We have also included the elastic constants and phonon dispersions to test the dynamic stability of the systems. Our theoretical findings bear fundamental interests in the development of complicated amorphous nanostructures.

Based on the framework of density functional theory (DFT), the structure, elastic, optical, Debye temperature and piezoelectric properties of tetragonal ${\mathrm{\text{BaTiO}}}_3$ (BT) individually doped with calcium (Ca) at barium (Ba) and zirconium (Zr) at titanium (Ti) site have been investigated by a first-principles technique. These properties of Ca and Zr (Ca/Zr) co-doped BT (BCZT) also have been investigated by the same calculation method. The effects of exchange and correlation functional on these properties are also investigated. The structural studies have demonstrated that the Ca-doped BT (BCT) exhibits the reduced volume due to radius of Ca smaller than that of Ba, while Zr-doped BT (BZT) presents the enlarged volume due to radius of Zr being larger than that of Ti. The as-calculated lattice parameters have verified the consistency of well-designed crystal structure with the experimental results. The investigations of the band structure demonstrated that the doping of Ca, Zr and Ca/Zr enlarges the band gap ($E_B$) of BT in sequence. Furthermore, the $E_B$ values obtained via HSE06 matched well with experimental values, while those obtained by generalized gradient approximation (GGA) and local density approximation (LDA) are significantly lower. The studies of optical, Debye temperature and elastic properties show that the BCZT displays a decreased refractive index, reduced thermal conductivity and an enhanced anisotropy index. Most importantly, after the co-doping of Ca and Zr, the piezoelectric strain tensor $d_{33}$ of BCZT increases by $\sim 125$% compared to that of BT. This work provides a theoretical guidance for improving the piezoelectric performance of BT via the doping strategy.

Using ab initio first-principles calculations, we investigate the structural, electronic, optical, and vibrational properties of Silver Sulphide Ag₃S and Selenide Ag₃Se with nonlocal hybrids exchange-correlation functional. With our computational predictions, we manage to classify the material to be Fermi-Dirac semi-metal, rather than Weyl metal. Our calculated results show that the electronic band in between the Fermi-Dirac cone shifts downward when we replace the element Sulphide S with Selenide Se. The obtained optical results such as absorption coefficients and dielectric functions (conductivity, reflectivity, etc.) are similar for both Ag₃S and Ag₃Se. A high absorption coefficient of $2\times 10^5$ cm${}^{-1}$ has been reported, and about 50% of light is reflected. In Raman spectra, the A${}_{\mathrm{\text{g}}}^{\mathrm{\text{X}}\text{-}\mathrm{\text{X}}}$ managed to shift downward when replacing the element X, sulphide S with selenide Se, while the A${}_{\mathrm{\text{g}}}^{\mathrm{\text{rigid}}}$ shifts upward (to higher wavelength). The rotation and vibration of the bonding between atoms have also been explained. The calculated results of Silver-VI compounds provide useful information in the exploitation of more complicated structures.

Ab Initio density functional theory (DFT) simulations have been employed to systematically explore the electronic, optical, elastic, mechanical and vibrational properties. In this study, we revealed that $\gamma$-CuI has a wide direct bandgap energy of 3.21 eV, is pure covalent and brittle. We also found that the core level is made up of I s electron orbitals, the valence band is constructed with I p orbitals, and the Cu s orbital states mainly contribute to the conduction band minimum (CBM). The reflectivity of CuI is reported to be low (35.9% for the light reflected), showing high material absorption. A high absorption coefficient of $2.31\times 10^5{\mathrm{\text{cm}}}^{-1}$ is also reported. The elastic and mechanical properties can further confirm the mechanical stability of the CuI system, derived from DFT-calculated elastic constants and phonon dispersion from density functional perturbation theory (DFPT) calculations.

In this paper, we will investigate the structural, electronic, mechanical, magnetic and optical properties of Heusler Mn₂NiAl (MNA) compound using the Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) of the full potential linearized augmented plane-wave method for exchange and use correlations, modified Becke–Johnson and GGA+U Hubbard parameter. The calculated band structure (BS) and density of states (DOS) of MNA showed a metallic (GGA), nearly half-metallic (mBJ) and half metallic (GGA+U) behavior. Moreover, the magnetic computed magnetic moments by GGA+U are higher compared to GGA and mBJ results. Bulk modulus, shear modulus, Voigt and Reuss polycrystalline elastic modulus, Debye temperature, sound velocities, the melting temperatures, $B/G$ ratio, Young’s modulus and Poisson’s ratio were obtained. The elastic anisotropy of MNA alloy was analyzed using 2D and 3D figures of directional dependence of Poisson’s ratio, shear modulus, linear compressibility and Young’s modulus. Studies have shown that the Heusler material MNA has magnetic and anisotropic properties and is mechanically stable.

Research Highlights

• •Electronic, magnetic, elastic and thermoelectric properties of RbCrC alloy are investigated.
• •Material is half-metallic, ductile and anisotropic in nature.
• •The total magnetic moment (3$\mu$B) obeys the Slater–Pauling rule.
• •The HM RbCrC compound is identified as potential candidate for spintronic applications.
• •ZT calculated values of 0.89 and 0.94 make RbCrC a promising thermoelectric material candidate for use in future devices.

The aim of this work is to investigate the half-metallicity behavior, elastic, thermodynamic and thermoelectric (TE) properties of the Heusler compound RbCrC using the generalized gradient approximation (GGA-PBE96) and the modified Becke–Johnson (mBJ) approach. The electronic band structures and density of states reveal that RbCrC is a half-metallic ferromagnet (HMF). The calculated total magnetic moment of 3$\mu$B follows the Slater–Pauling rule ($M_{\mathrm{\text{tot}}}=Z_{\mathrm{\text{tot}}}-8$). The half-metallicity character can be maintained in the 5.4–7.4 Å lattice constants range and the 0.8–1.2 $c$/$a$ ratio range. Existence of half-metallic ferromagnetism in RbCrC makes it a promising material for practical applications in the spintronic field. Also, the RbCrC exhibits a ductile and anisotropic behavior. The quasi-harmonic Debye model (QHDM) is used to calculate the thermodynamic properties. The BoltzTraP code which is based on semi-classical Boltzmann theory (SCBT) is applied for calculating TE properties. According to the obtained figure of merit values (ZT between 0.89 and 0.94 from 50 K to 800 K), the RbCrC alloy remains a good candidate for thermoelectric applications.