With the rapid expansion of material application, the limitation of single layer material has become more apparent and its intrinsic properties can no longer satisfy the growing demand. Construction of...

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Yttrium niobate (YNbO 4 ) phosphor is studied experimentally and through first-principles calculations, in which the structural and electronic properties of YNbO 4 are investigated using the local-density approximation LDA+U method. The absorption and luminescence experiments that were conducted on the host lattice show the band gap to be ≈ 4.1 eV. The LDA+U calculations allow us to obtain a band gap of 4.28 eV. The density of states obtained from the calculation shows that O 2p states contribute to the valence band. The lower conduction band is mainly composed of Nb 4d states, while the upper conduction bands involve contribution mainly from Y 4d states. The partial DOS of each atom in the niobate system is then compared to the ultraviolet (UV) and vacuum ultraviolet (VUV) spectra from A photoluminescence excitation (PLE) experiment to explain the nature of the bands observed.

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Superhard materials are indispensable for use in cutting and polishing, as well as for nuclear reactor construction. As a candidate for hard material, ZrC has been extensively studied but not in its pressurized phase. Through evolutionary algorithm and density functional theory, we narrowed down the stoichiometry of Zr and C elements at various elevated pressures. The semimetal property of Zr4C4 continues to exist at high pressures but with lower electrical conductivity. Ionic and covalent bonding coexist around the pseudogap for high pressure phases. Both elastic constants and elastic moduli are found to increase steadily with surrounding pressure, connoting the superior mechanical and thermal characteristics of Zr4C4. This can be seen in the increased hardness values, higher melting temperatures, and better machinability indices for Zr4C4 as pressure rises. The predicted G/B and Poison's ratios have both agreed that Zr4C4 exhibits a transition from brittle to ductile behavior when the applied pressure goes above 85 GPa, displaying an overall improved mechanical performance.